Revision on unit 1
Starch
Starch is a polymer (i.e. polysaccharide) whose monomers are a-glucose molecules, that are joined together
by glycosidic bonds.
Starch is a polymer of a-glucose, so it stores a lot of energy.
Starch is a mixture of two substance, amylose and amylopectin.
Amylose releases glucose more slowly overtime keeping you going longer whereas amylopectin releases
glucose for cellular respiration, rapidly when needed.
Amylose
It is a polysaccharide made by the condensation of a-glucose that are joined together by 1-4 glycosidic bond.
Amylose has a non branching (i.e. linear) chain where the chain is coiled forming helical (i.e. spiral) structure,
making the final molecule more compact, so it takes up less space, with more glucose being stored in smaller
space, so it doesn’t get into the way of organelles or substances moving around in cell.
Amylopectin
It is a polysaccharide made by the condensation of a-glucose that are linked together by 1-4 and 1-6
glycosidic bonds. Amylopectin has a branching chain formed by 1-6 glycosidic bonds so starch is quickly
hydrolyzed, but chains are shorter than amylose.
This structure causes amylopectin to be insoluble, compact (i.e. takes up less space) with high density, and
rapidly hydrolyzed and so this make starch have a metabolic function by being a convenient energy storage
molecule.
Note that, a mixture of amylose and amylopectin build up into large starch grains found in
chloroplast and in storage organs such as potato tubers and seeds.
Glycogen
Glycogen is a polymer (i.e. polysaccharide) whose subunits are a-glucose molecules that are linked
together by 1-4 and 1-6 glycosidic bonds. Glycogen is an energy storage molecule that is similar in
structure to amylopectin but is more branched, so that glucose can be rapidly released (i.e. glycogen
rapidly hydrolyzed) for cellular respiration in cells to provide energy when needed. Also, for rapid storage
of glucose in cells.
Note that, glycogen tend to clump together to form granules, which are visible in liver and muscle cells,
where they form energy reserve.
Properties of glycogen that makes it a good storage molecule
•Low solubility or insoluble, so it won’t lower the water potential nor the osmotic pressure inside cells, so
no effect on chemical reactions inside cells.
•Many terminals (i.e. ends) for easy attachment and removal of glucose (highly branched)
•Glucose can be stored quickly.
•Rapidly hydrolyzed by specific enzymes giving glucose easily and quickly when required for respiration
and energy release.
•The structure of glycogen makes it more compact, thus taking up less space (allow storage of large
quantities of glucose in a small space), such that it does not get into the way of organelles or substances
moving around inside the cell.
Globular proteins
•Globular proteins are water soluble, this is because amino acids with hydrophilic polar R groups
are facing outwards -so hydrogen bonds are formed with water- while amino acids with
hydrophobic non polar R groups are pointing inside towards the center of the molecule.
•They curl up into spherical (globular) shape and have tertiary structure with specific 3D shape
making them metabolically active.
(Some have quaternary structure)
•Many globular proteins have metabolic functions, so if their shape is altered slightly by changing
conditions, they lose their ability to function.
•Examples include hemoglobin, myoglobin, insulin, antibodies, and enzymes.
•Note that, globular proteins do not fully dissolve to make a solution, instead the molecules are so
big, forming a colloid (a suspension of molecules that are not fully dissolved).
How amino acids join together to form the 3D structure of protein?
•Formation of peptide bond between amino group of one amino acid and carboxyl group of
another.
•Primary structure is the sequence of amino acids in polypeptide chain.
•This determines the position of R groups, orientation and arrangement, and also the type of
bonds between R groups of amino acids (i.e. the R group interaction including hydrogen bonds
between polar groups, disulfide bonds between cysteine SH groups, ionic bonding between
ionized amine and carboxylic acid groups and hydrophobic interaction between non polar side
chains).
•This in turn determines the overall folding and coiling of polypeptide chain into tertiary structure
giving a specific shape of active site which is complimentary to substrate.
•Moreover, amino acids with hydrophilic polar R groups are facing outwards, while amino acids
with hydrophobic non polar R groups are pointing inside to the center of the molecule making it
water soluble as enzymes are globular proteins with tertiary structure.
•Form specific shape of active site.
Fibrous protein
Have simpler structure (no tertiary structure), with polypeptides lying parallel to each other so
more stable to changes in pH and temperature. They don’t curl up but form long strands with
many cross links (cross linked chains). They are water insoluble with large number of repeating
amino acid sequences. Fibrous proteins have structural function, being very tough thus giving
strength.
•Keratin found in nails, hair and the outer layer of the skin making these structures waterproof.
•Collagen (structural protein) provides strength to the artery wall, as blood pressure is high in
arteries.
Comparison between Fibrous and Globular proteins
•Fibrous proteins have a long strand, narrow fiber like structure and have no tertiary
structure (no complex folding). While globular proteins have round (spherical) shape with
tertiary structure (complex folding) and sometimes quaternary structure.
•Fibrous proteins have structural function while globular proteins have metabolic function.
•Fibrous proteins have large number of repeating amino acid sequences while globular
proteins have irregular amino acid sequence.
•Fibrous proteins are more stable and are less sensitive to changes in pH and
temperature while globular proteins are more sensitive to changes in temperature and pH.
•Fibrous proteins are insoluble in water, with non polar R groups facing outwards while
globular proteins are soluble in water with hydrophilic R groups facing outwards.
•Examples of fibrous protein includes (collagen in tendons, keratin, myosin in muscles).
Examples of globular proteins include (hemoglobin, myoglobin, immunoglobulin, insulin
and enzymes)
Secondary structure
•It is the regular folding or coiling of polypeptide chain, held in shape by
hydrogen bonding between the oxygen of -CO- group of one amino acid and
the hydrogen of the -NH- group of another amino acid.
•(Note that, R groups are not involved in secondary structure)
•Types of folding include (a-helix and b-pleated sheet)
a-helix
•The polypeptide is coiled into a spiral shape.
•Hydrogen bonds between amino acids in the same polypeptide chain
stabilize the a-helix structure, with peptide bonds forming backbone and R
groups protruding in all directions.
b-pleated sheet
•Much looser and straighter in shape than a-helix.
•Polypeptide chain is held into regular, parallel pleats (i.e. flat sheets).
•Held together by hydrogen bonds between the amino and carboxyl groups
of amino acids.
Collagen
•Collagen is an insoluble, fibrous protein, found in tendons, cartilage,
bones, teeth and walls of blood vessels.
•It is made up of three polypeptide chains (i.e. have quaternary
structure), each in a shape of helix but not a-helix as it is not tightly
wound.
•Glycine -the smallest amino acid- is repeated every third position in
each polypeptide.
•The three helical polypeptides are wound around each other forming
triple helix (i.e. helical structure).
•Which are held together by many hydrogen bonds.
•Also, they are held by covalent bonds -cross links- between collagen
molecules lying parallel to each other (between the R groups of amino
acids lying next to each other) to form fibrils.
•Many fibrils lie along each other forming strong bundles called fibers.
•This structure gives collagen high tensile strength, where it can
withstand large pulling forces without stretching or breaking.
•Note that, collagen is found in walls of arteries to withstand high blood
pressure and prevent over-stretching thus preventing bursting or
rapture.
•Genetic disease called osteogenesis imperfecta causes the collagen
triple helix not to develop properly so the bone doesn’t have much tensile
strength, so it becomes brittle and breaks easily.
Conjugated proteins
These are protein molecules attached to (conjugated to) another molecules
known as prosthetic group (i.e. molecules not made up of amino acids)
Examples include hemoglobin, lipoproteins and glycoproteins.
Hemoglobin
Lipoproteins
Glycoproteins
giving globular structure).
•Where lipoproteins have an
prosthetic group, where
•It is globular in shape (where •These are protein molecules that •These are proteins with
carbohydrates
four polypeptide chains fold are conjugated with lipids.
•Water soluble, as amino
important role in the transport of
Fe2+ ion attached to a
causes accumulation -i.e. build up-
the carbohydrate part
helps them to hold a lot
cholesterol
in
blood.
acids with polar hydrophilic R
of water and also makes
•As
triglycerides
are
insoluble,
so
groups are facing cytosol
it harder for protein
they are conjugated with proteins digesting enzymes (i.e.
(i.e. cytoplasm) forming
forming lipoproteins -either LDL proteases) to break
hydrogen bond with water.
or HDL- formed into vesicles.
them down.
•It is made up of four
•LDL contains saturated fat,
•Examples include,
polypeptide chains (2a and
mucus and synovial fluid
cholesterol and proteins
2b of globins) and therefore,
-apoproteins- while HDL contains which reduces friction.
has quaternary structure.
unsaturated fats, cholesterol and Where mucus is
•Each polypeptide chain has
produced in the stomach
protein.
to protect protein walls
a heam group (i.e. prosthetic
•LDL carries cholesterol to your
from digestion.
group which is not made up of cells where it binds to the cell
amino acids) made up of
membrane (yet too much LDL
porphyrin ring to bind with
oxygen forming
oxyhemoglobin.
of cholesterol in artery walls
causing them to narrow). While
HDL carries excess cholesterol
•So, four polypeptides (heam from body tissue back to the liver
groups) carry four oxygen
where it is broken down and
molecules (4O2)
removed from the body.
•Note that, HDL contains more
proteins than LDLs which is
partially why they are more dense,
as proteins are more compact
molecules than lipids.
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1A.3. Carbohydrates 2: Polysaccharides
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•Replacing lost water.
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1A. 3. Carbohydrates 2: polysaccharides
•Where extra water lowers the solute potential in the lumen.
•Therefore, less water enters the lumen from the blood (i.e. reduces
osmosis from blood).
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•Also, starch is a polysaccharide so it is insoluble, and therefore has no
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osmotic effect.
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The linear sequence of amino acids in a polypeptide chain that are joined
together by peptide bonds.
The primary structure of enzymes (i.e. the sequence of bases in polypeptide
chain) determines the position, orientation and arrangement of R groups of
amino acids, which in turn determines the interaction (i.e. bonding between R
groups) including hydrogen bonds between polar groups, ionic bond between
ionized amine and carboxylic acid groups, disulfide bond between cysteine
groups as well as hydrophobic interaction between non polar side chains,
that determines the overall folding and coiling of polypeptide chain giving a
specific three dimensional shape of protein. Where enzymes are globular
proteins, meaning that their three dimensional shape makes them
metabolically active, so they have specific shape of active site which is
complimentary to specific substrate also, they are water soluble as amino
acids with non polar hydrophobic R groups are pointing inwards towards the
center of the molecule.
Biology
Topic 1: Molecules, transport and health
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a-glucose and b-galactose join together by condensation reaction involving
the loss of water molecule and causing the formation of 1-4 glycosidic
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bonds.
Enzymes are specific, where each enzyme has a specific shape of
their active site which is determined by specific sequence of amino
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acids with specific R groups that is maintained by R group
interaction including hydrogen bonds between polar groups, ionic
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bonds between ionized amine and carboxylic acid groups, disulfide
bonds between cysteine SH groups and hydrophobic interaction
between non polar side chains. The active site of enzyme is
complimentary in shape to one substrate only, therefore one
substrate can bind to specific enzyme forming enzyme substrate
complex. Where the shape of glucose and galactose are different so
they require different enzymes.
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Linked to 2B.2.
How enzymes
work
Biology
Topic 1: Molecules, transport and health
Small
Large
Monosaccharides are composed of a single sugar unit while polysaccharides are composed
•Monosaccharides
cannot be
Monosaccharides have no glycosidic bonds while polysaccharides have glycosidic bonds
holding monomers together.
hydrolysed while
Linked to 1A.3.
Carbohydrates 2:
Polysaccharides
Monosaccharides are sweet, and soluble with osmotic effect while polysaccharides are non
can be hydrolysed
sweet and insoluble with no effect on water potential (i.e. no osmotic effect).
Monosaccharides are reducing sugars with reducing end (i.e. free functional group) while
polysaccharides are non reducing sugars with no free functional group.
Monosaccharides have general formula (CH2O)n while polysaccharides have general
1A.5. Proteins
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formula (C6H10O5)n
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polysaccharides
of many sugar units.
Fibrous protein involves polypeptides arranged parallel to each other
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thus being stable to changes in pH and temperature. They don’t curl up
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(i.e. polypeptide chains don’t curl up so no tertiary structure) but form
long strands with many cross links (i.e. cross linked chains). Fibrous
proteins are water insoluble with many repeating amino acid sequences.
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They have structural function, being very though thus giving strength.
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Biology
Topic 1: Molecules, transport and health
1A. 5. Proteins
(3)
Blood pressure in arteries is high. Where collagen is a fibrous
protein, having structural function, being tough thus giving
Linked to 1B.3.
Circulation in
strength, the blood
vessels
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where collagen is found in artery walls, thus preventing over
stretching of arteries under high pressure and therefore prevents
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rupture. Therefore, alteration in the structure of collagen or reduced
causing it to rupture.
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collagen causes over stretching of arteries under high pressure thus
Note that, triglycerides are non polar
hydrophobic molecules that are insoluble in
water, thus being conjugated to proteins
forming lipoproteins (including LDL and HDL)
formed into vesicles to be transported in the
blood.
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Biology
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Monounsaturated with one carbon to carbon double bond
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Fatty acid with hydrocarbon chain
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Topic 1: Molecules, transport and health
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Oleic acid is a mono unsaturated fatty acid with one carbon to carbon
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double bond in hydrocarbon chain.
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Biology
Topic 1: Molecules, transport and health
Fatty acids have different numbers of carbon to carbon double bonds.
Where as the number of carbon to carbon double bonds increases, the
melting point decreases as hydrocarbon tails become more bent (i.e. with
more kinks) so they pack less closely together. So the intermolecular
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forces and separate fatty acid chains.
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forces are weaker and less energy is needed to overcome intermolecular
•Ester (COO-) bond
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•Water molecule
Condensation reaction
Esterification
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Biology
Topic 1: Molecules, transport and health
Lactose is a disaccharide, which is composed of the two sugar units, a-glucose and galactose
while starch is a polysaccharide, which is composed of a-glucose monomers only. Lactose has a
free functional group (i.e. is a reducing sugar) while starch is not a reducing sugar with no free
Also, lactose has 1,4 glycosidic bond while starch has both 1,4
functional group.
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and 1,6 glycosidic bonds.
As the mass of milk in diet increases, the relative risk of death increases
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(i.e. positive correlation).
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Biology
Topic 1: Molecules, transport and health
Glycogen is a polysaccharide, which is composed of a-glucose monomers that are
linked together by 1-4 and 1-6 glycosidic bonds. Where it is compact, thus
allowing storage of large number of glucose in small space and also has a
branching structure causing glycogen to have many terminals (i.e. ends) for easy
attachment and removal of glucose for cellular respiration, thus releasing energy
as ATP for muscle contraction. In addition to that, glycogen is insoluble, thus
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1A.4. Lipids
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having no osmotic effect, so it has no effect on water potential of cells.
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Ester bond
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Rapidly
hydrolysed
Topic 1: Molecules, transport and health
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Biology
Saturated fatty acids have no double bonds between carbon atoms while
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unsaturated fatty acids have double bonds between carbon atoms. Saturated
fatty acids have straight hydrocarbon chain while the hydrocarbon chain of
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unsaturated fatty acids has kinks (i.e. is bent). Also, the hydrogen to carbon
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ratio is higher is saturated fatty acids.
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1A.2. Carbohydrates 1: mono & disaccharides
a-glucose and fructose
Sucrose is a disaccharide, formed by the condensation reaction between a-glucose
and fructose, that involves the removal of water molecule, causing the formation of
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1-2 glycosidic bond between the two monosaccharides.
1A.3. Carbohydrates 2
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(4)
Starch is a polysaccharide (polymer) whose subunits are a-glucose molecules linked
together by glycosidic bond. Where starch is made up of amylose and amylopectin,
where amylose is a polysaccharide with a coiled, helical structure with a-glucose
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molecules joined by 1-4 glycosidic bonds, whereas amylopectin is a polysaccharide
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with branching structure with glucose molecules linked by 1-4 and 1-6 glycosidic
bonds. Amylopectin has many terminals for rapid condensation and hydrolysis, for
easy attachment and removal of glucose for cellular respiration in cells to release
energy in the form of ATP.
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Topic 1: Molecules, transport and health
Peptide bond
Polypeptide
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Water molecule
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1A.1. The chemistry of life
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Water is dipolar, with slightly negative oxygen and slightly positive
hydrogen. Therefore, it is a solvent, where polar molecules dissolve by
forming hydrogen bonds with water such as oxygen, carbon dioxide and
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glucose. Also, ions dissociate in water where S- oxygen is attracted to
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cation (+ve ion) and S+ hydrogen is attracted to anion (-ve ion).
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Formation of blood clot
•Upon a cut in a tissue, the contact between platelets and the cut tissue
(collagen fibers in skin) causes platelets to break open in large numbers
and release serotonin and thromboplastin.
•Serotonin causes the construction of blood vessels, narrowing
(constricting) blood vessels, thus cutting off blood flow to the damaged
area,thus preventing excessive loss of blood.
•Thromboplastin (enzyme that starts the blood clotting cascade of
reactions), however is a soluble protein (biologically inactive) that, in the
presence of calcium ions in the right concentration, catalyses the
conversion of large soluble protein prothrombin (biologically inactive) into
a soluble protein called thrombin enzyme (biologically active).
•Thrombin then catalyses the conversion of soluble globular plasma
protein, fibrinogen into the insoluble protein fibrin, which forms a mesh
(fibrous mesh) trapping blood cells and platelets to form a clot.
•Special proteins in the structure of platelets contract, making the clot
tighter and tougher to form a scab that protects the skin and the vessels
underneath as they heal, also preventing entry of bacteria.
•Note that, narrowed blood capillaries prevent excessive bleeding by
allowing less blood flow near skin surface so blood clots.
•Fibrinogen is a soluble, globular protein with hydrophilic R groups of
amino acids facing outside.
Red blood cells (erythrocytes) are specialized cells containing hemoglobin which carries oxygen from the
lungs to all body cells.
Hemoglobin
•Hemoglobin is a protein molecule which is made up of four subunits (four polypeptide chains) meaning
that it has a quaternary structure.
•Each polypeptide chain has a Heam group (containing Fe2+ and propherin ring) where an oxygen
molecule binds to each of the four heam groups.
•Hemoglobin plays a role in the transport of both oxygen and carbon dioxide.
Role of hemoglobin in the transport of oxygen
•Each hemoglobin molecule binds reversibly with four
oxygen molecules forming oxyhemoglobin.
•The oxygen remains bound to hemoglobin until the blood
reaches an area of low partial pressure of oxygen (i.e.
high PCO2).
•Note that, partial pressure is the pressure exerted by one
type of gas in a mixture of gases.
Role of hemoglobin in the transport of carbon dioxide
•Carbon dioxide binds to the -NH2 group (amino group) of hemoglobin
forming carbamino hemoglobin.
•Carbon dioxide remains bound till the blood reaches an area of low partial
pressure of carbon dioxide (i.e. high PO2)
Hemoglobin dissociation curve
•Dissociation curve reflects the way that oxygen molecules bind to hemoglobin and it aims to
show how hemoglobin behaves at different concentrations (i.e. partial pressures) of oxygen.
At low partial pressures of oxygen
(in respiring cells), the percentage
saturation of haemoglobin is very low
that is, the haemoglobin is combined
with only a very little oxygen.
At high partial pressures of oxygen
(in lungs), the percentage saturation
of haemoglobin is very high such that
it is combined with large amounts of
oxygen.
In lungs
There is high concentration of oxygen (i.e. high partial pressure of oxygen), while
the concentration of oxygen in red blood cells is relatively low, so oxygen diffuses
from the air in lungs, down the concentration gradient into red blood cells.
Hemoglobin has higher affinity for oxygen due to the high partial pressure of
oxygen, so oxygen is being loaded to hemoglobin.
So, the percentage saturation of hemoglobin with oxygen increases (forming
oxyhemoglobin).
The binding of oxygen to hemoglobin and the formation of oxyhemoglobin reduces
the percentage of free oxygen in the cytoplasm of red blood cells thus, maintaining
steep concentration gradient for more diffusion of oxygen into red blood cells.
In tissues (respiring cells)
The concentration of oxygen in body tissues is relatively low (i.e. low partial
pressure of oxygen) while in the cytoplasm of red blood cells is higher. Where at low
PO2, (i.e. high PCO2) hemoglobin has lower affinity to oxygen, so more
oxyhemoglobin dissociation, so oxygen diffuses into respiring cells down the
concentration gradient.
All in all, in lungs, hemoglobin picks up oxygen where the partial pressure of
oxygen is high (i.e. low PCO2), where hemoglobin will be 95-97% saturated with
oxygen. Whereas in respiring cells, hemoglobin releases oxygen, where the partial
pressure of oxygen is low (i.e. PCO2 is high), where hemoglobin will be about
20-25% saturated with oxygen.
This means that Hb coming from the lungs carries a lot of oxygen, as it reaches a muscle
(i.e. respiring tissue) it releases around three-quarters of it. This released oxygen diffuses
out of the red blood cell and into the muscle where it can be used in respiration.
So, PO2 decreases as blood flows through arteries and into veins.
As arteries take blood to cells, while veins take blood away from cells so O2 diffuse out
of capillaries into cells because there is a lower PO2 in cells and CO2 increase in blood
by diffusion down concentration gradient.
Why the hemoglobin dissociation curve is s-shaped? (Allosteric mechanism)
•Hemoglobin is a protein molecule that has a quaternary structure and is made up of
four subunits (four polypeptides) with four heam groups (i.e. prosthetic group, with
Fe2+ and porpherin ring) where an oxygen molecule binds to each of the Fe atoms until
the hemoglobin molecule becomes fully saturated with four oxygen molecules (i.e. eight
oxygen atoms).
•The binding of the first oxygen molecule is difficult where is binds to an iron atom in a
heam group.
•The whole hemoglobin molecule becomes slightly distorted as many molecules will be
broken down causing a conformational change in the structure of hemoglobin.
•The distortion makes it easier for other molecules to combine with heam groups the
hemoglobin affinity to oxygen increases.
•As the hemoglobin becomes more saturated, less oxygen can bind so the curve
flattens out. This is known as the allosteric mechanism.
Note that,
The same process happens in reverse when oxygen dissociates from haemoglobin
where it gets progressively harder to remove the oxygen.
Marking scheme points
•Hemoglobin is composed of four subunits
•The binding of the first oxygen molecule is difficult
•The binding of other molecules become easier
•Due to a confirmational change
•As Hb becomes more saturated, less oxygen can bind so the curve flattens out.
The Bohr effect
The CO2 causes the hemoglobin dissociation curve to shift, this is called the Bohr
effect.
The curve shifts right
This is because, when the concentration of CO2 in our blood increases (for example,
during exercise)
This lowers the pH of the blood
That in turn reduces the affinity of hemoglobin for oxygen
And that is because hemoglobin changes shape (acidic medium)
Making it harder for oxygen molecules to bind
This increases the amount of oxygen being unloaded with hemoglobin (increasing the
dissociation of oxygen).
To be released for respiring tissues where it can be used in aerobic respiration.
Note that, due to the Bohr effect, at a particular partial pressure of oxygen, the
percentage saturation of hemoglobin with oxygen will be lower.
Organisms can be adapted to their environment by having different types of hemoglobin with different transport properties.
Hemoglobin is a protein molecule, which is composed of amino acids and when the sequence of amino acids changes, hemoglobin
can have a different structure.
This is because its primary structure changes resulting in it folding in a slightly different way. This results in it having a different
shape as well as different affinity for oxygen.
This is why in some organisms, the dissociation curve shifts left, while in others which are more active, the dissociation curve shifts
right.
When the curve is shifted to the left,
The hemoglobin affinity to oxygen is increased
This means that it loads oxygen (i.e. binds to oxygen) more readily at lower partial pressure of O2.
Example of organisms having such properties is those at higher altitude, underground or in fetal blood (i.e. in low oxygen
environment)
Fetal hemoglobin has higher affinity to oxygen than adult hemoglobin,
This is important because by the time the mother’s hemoglobin reaches the placenta, its oxygen saturation has decreased
which is because some has been used up by the mother’s body.
Therefore, fetal hemoglobin needs to be better at absorbing oxygen than the mother’s hemoglobin so that the fetus can
still get oxygen from its mother’s blood across the placenta.
Fetal hemoglobin
•Fetus depends on its mother to supply it with oxygen.
•If blood of fetus had same affinity for oxygen as the blood of mother, very little oxygen would be transferred.
•Therefore, fetal haemoglobin has higher affinity for oxygen than adult haemoglobin so, can remove oxygen from maternal
blood even at low PO2.
•In addition, maternal and fetal blood run in opposite directions thus maintaining a steep concentration gradient between
mother’s blood and that of fetus.
When the curve is shifted to the right,
This means that the hemoglobin affinity to oxygen is lowered. Therefore, at low pO2 the percentage saturation of hemoglobin
with oxygen is lower and this means that more oxygen has been unloaded to the tissues (i.e. more dissociation of oxygen).
This is present in organisms that need more oxygen in their tissues,
For example, those with high metabolic rate that are either small or active requiring more oxygen.
Carbon dioxide influences the percentage saturation of Hb with oxygen.
•Where in cells with high rate of aerobic respiration (i.e. active cells), where there is high demand of
oxygen, and high partial pressure of carbon dioxide. The affinity of haemoglobin for oxygen is reduced.
So, hemoglobin releases more oxygen much more easily (i.e more oxyhaemoglobin dissociation) than it
would be at lower concentration of carbon dioxide. So more oxygen is readily available for respiring
cells to meet increased energy demands (i.e. to provide sufficient oxygen for respiration).
•While in lung capillaries, where the carbon dioxide levels are relatively low (i.e. low PCO2), making it
easier for oxygen to bind to the hemoglobin (i.e. increasing the affinity of hemoglobin for oxygen).
Role of carbon dioxide in unloading of oxygen from hemoglobin
•Carbon dioxide diffuses down steep concentration gradient from tissue into capillaries, where it is carried in
the blood in three ways, 5% of CO2 is carried as undissociated CO2 in plasma, 85% as hydrogen
carbonate ions in solution in plasma and 10% combined with -NH2 group of hemoglobin forming carbamino
hemoglobin.
•Carbonic anhydrase is an enzyme which catalyses the reaction between carbon dioxide and water in the
cytoplasm of RBC, to form carbonic acid, which occurs very fast thus maintaining steep concentration
gradient for diffusion of carbon dioxide from tissues into the blood.
•Carbonic acid then dissociates into hydrogen ions (H+) and hydrogen carbonate ions (HCO3-).
Hydrogen carbonate ions
•HCO3 will diffuse out of red blood cells into plasma, where 80-90% of CO2 is transported as hydrogen
carbonate ions in the plasma. Where the reaction maintains the concentration gradient for carbon dioxide
between blood and respiring tissues. Where if carbon dioxide was transported as CO2 which is acidic, the pH
would decrease but HCO3 ions are alkaline thus acting as buffer.
Hydrogen ions
•Hemoglobin has higher affinity for hydrogen ions than oxygen, where hydrogen ions react with hemoglobin
forming hemoglobinic acid (HHb), i.e. hydrogen promotes the oxyhemoglobin dissociation by causing change
in the tertiary structure of oxyhemoglobin causing release of oxygen. Thus increasing the supply of oxygen to
respiring tissues.
(This is why higher PCO2, causes hemoglobin to release more oxygen -Bohr shift-).
Formation of carbamino hemoglobin
•Hemoglobin has higher affinity for carbon dioxide than oxygen, so in high PCO2, some carbon dioxide in
RBCs combine with terminal amino groups (-NH2) of some hemoglobin molecules, forming carbamino
hemoglobin, thus stimulating hemoglobin to release more oxygen in areas of low PO2, where 10% of CO2 is
transported thus way.
•Note that, as CO2 builds up, this affects pH and has an effect on protein structure, where hemoglobin has
lower affinity to oxygen.
•when blood reaches the lungs, the alveoli has low PCO2 and high PO2, so carbon dioxide
will diffuse out of the blood into the air in the alveoli.
•which stimulates the CO2 in the carbamino hemoglobin to leave the RBCs.
•and hydrogen carbonate and hydrogen ions to recombine forming carbon dioxide molecules
once more (where carbonic anhydrase catalyses the reverse reaction in lungs and hydrogen
ions act as buffer in plasma).
•this leaves hemoglobin molecules free to combine with oxygen and begin another circuit.
•Dissociation curve of C is shifted to the left in respect
to B dissociation curve.
•hemoglobin affinity in C is lowered.
•where at low PO2, the percentage saturation of
hemoglobin with oxygen is lower in C than in B.
•where C needs more oxygen for more respiration for
more activity and higher metabolic rate.
•in addition to large surface area to volume ratio, so
more heat loss, so more respiration to maintain
constant body temperature.
At high altitudes
The partial pressure of oxygen (i.e. PO2), is lower than in sea level, so less oxygen in
inhaled air, so lower partial pressure of oxygen in the alveoli (lungs), thus reducing
-decreasing- the steepness of the concentration gradient between alveoli and the blood, so
slower rate of diffusion of oxygen into the blood. Meaning that hemoglobin is less well
saturated with oxygen, so less formation of oxyhemoglobin (i.e. hemoglobin has lower
affinity to oxygen).
Therefore, less oxygen will be transported in the blood, so less oxygen is available for
aerobic respiration, so less aerobic respiration which results in altitude sickness and
hypoxia.
Solution
•They produce more RBCs, to compensate for the smaller volume of oxygen absorbed
(lower saturation of hemoglobin).
•Increase in breathing rate and heart rate.
•In addition to increase in capillary density and number of mitochondria so tissues can
sufficient oxygen.
•Note that, as a result of the low PO2 at high altitudes, the hemoglobin affinity for oxygen
is reduced, so lower percentage saturation of hemoglobin with oxygen at high altitudes
than at sea level.
•hypoxia occurs when person ascends from sea level to a high altitude, where body tissues
don’t receive an adequate supply of oxygen.
•plus, person has insufficient RBCs to compensate for the reduced affinity of HB for O2.
Biology
Topic 1: Molecules, transport and health
Aorta has semilunar valves thus preventing the back flow of blood into the heart during ventricular diastole.
In addition, it is branching to supply blood to different parts of the body.
Aorta is an artery with narrow lumen, to maintain blood flow under high pressure. Also, it has tunica intima
(endothelium) which is composed of thin, flat squamous epithelial cells with smooth surface facing lumen to smooth out
the flow of blood allowing easy blood flow with minimum possible frictional resistance to blood flow, endothelial layer is
folded, to prevent damage to the endothelial lining when diameter of aorta increases. Thick tunica media which is
composed of smooth muscles, collage and elastic tissue. Where smooth muscles contract and relax changing the
volume of blood delivered by changing diameter of artery, collagen provides strength to withstand high blood pressure
thus preventing rapture, while elastic fibers stretch and recoil to accommodate increased blood pressure as well as
ab
r
maintain blood pressure and rapid blood flow. Thick tunica externa (i.e. thick walls) containing collagen and elastic
lG
fibers to provide strength and flexibility to artery.
Ni
ha
Veins have semilunar valves while capillaries have no valves.
ag
wa
n
are one cell thick.
&
Veins have walls containing smooth muscles and elastic tissue while capillaries have walls that
1B. 5. Atherosclerosis:
(5)
.N
Coronary artery supplies the heart muscle with oxygen and nutrients,
where the region of dead heart muscle will be downstream of the
Dr
atheroma (i.e. in region normally supplied by blocked artery). This is
because the region of cardiac muscle supplied by the blocked artery
becomes deprived of oxygen and nutrients, so no aerobic respiration
and therefore die due to lack of energy. So, the closer the atheroma is to
the end of artery the smaller the area of dead heart muscle and vise
versa.
Dr.Nagwan Gabr& Dr. Nihal Gabr
062
Biology
Topic 1: Molecules, transport and health
1B. 4. The mammalian heart
(2)
Atrioventricular valves do not shut properly, which results in back flow of
ab
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blood from ventricles to the atria during ventricular systole. Resulting in
May 2014
Code: WBI01/01
1B.4. The mammalian heart
Dr
.N
ag
wa
n
&
3
Ni
ha
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lower blood pressure so less efficient supply of oxygen to body cells.
Dr.Nagwan Gabr& Dr. Nihal Gabr
Atria systole
Ventricular systole
(Atrial and ventricular) Diastole
066
Paper 1
Biology
Topic 1: Molecules, transport and health
75
1B.3.Circulation in the blood vessels
&
Ni
ha
lG
ab
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(2)
Pressure
in ventricles
ag
wa
n
increases
to higher than
pressure in
Dr
.N
atria.
Atrial
systole
Dr.Nagwan Gabr& Dr. Nihal Gabr
Ventricular systole
067
Diastole
Biology
Topic 1: Molecules, transport and health
16KPa
&
Ni
ha
lG
ab
r
The pressure in ventricles increases to higher than pressure in atrium.
The semilunar valves open to allow blood to flow from the left ventricle
ag
wa
n
to the aorta to be transported to all the body. Therefore, the pressure in
aorta increased as blood surges into it under high pressure during
Dr
.N
ventricular systole.
Aorta walls have elastic fibers that stretch and recoil. Also, semilunar
valves close.
Dr.Nagwan Gabr& Dr. Nihal Gabr
068
Topic 1: Molecules, transport and health
1B.5. Atherosclerosis
&
Ni
ha
lG
(4)
ab
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Biology
Dr
.N
(8)
ag
wa
n
1B.1. The principle of circulation
Dr.Nagwan Gabr& Dr. Nihal Gabr
077
Topic 1: Molecules, transport and health
ag
wa
n
&
Ni
ha
lG
ab
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Biology
Peak flow rate is greater in men than in women, the peak flow rate is greatest in
men at the age of 35-38 and women at the age of 30-32.
Dr
.N
On average, men have larger lungs than women.
Graph will have similar shape and will be higher than that for women of 175cm.
Dr.Nagwan Gabr& Dr. Nihal Gabr
078
Biology
Topic 1: Molecules, transport and health
1B.2. The role of the blood
lG
ab
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(5)
Ni
ha
Upon a cut in a tissue, the contact between platelets and collagen fibers causes platelets to
break open in large numbers and release serotonin and thromboplastin. Thromboplastin is an
enzyme that starts the clotting cascade of reactions where in the presence of calcium ions in
the right concentration cause the conversion of prothrombin into thrombin, which in turn
&
catalyses the conversion of the soluble, globular protein, fibrinogen into fibrin, which forms
ag
wa
n
fibrous mesh, trapping blood cells and platelets to form a clot.
The blood clots formed in veins is carried through the pulmonary artery to pulmonary
capillaries in lungs, where it blocks the flow of blood, so reduced blood flow in lungs, so
reduced gas exchange. Reduced uptake of oxygen accompanied by usage of oxygen by
Dr
.N
respiring cells causes reduction in the concentration of oxygen in patients with VTE.
Changes in breathing rate or oxygen concentration may be due to another cause. As
well as fibrin fragments can be found in both VTE and non-VTE patients.
Therefore, using three criteria increases diagnostic accuracy.
Dr.Nagwan Gabr& Dr. Nihal Gabr
089
Topic 1: Molecules, transport and health
Dr
.N
ag
wa
n
&
Ni
ha
lG
ab
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Biology
Dr.Nagwan Gabr& Dr. Nihal Gabr
095
Biology
Topic 1: Molecules, transport and health
&
Ni
ha
lG
ab
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1B.2. The role of the blood
(8) c-
ag
wa
n
1B.2. The role of the blood
.N
Fibrinogen is a soluble globular protein, which is converted into insoluble,
Dr
fibrous protein, fibrin. Where peptide bonds between amino acids are
broken down by protease enzyme by condensation reaction. Fibrin sticks
together, forming fibrous mesh, trapping blood cells and platelets to form
a clot.
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097
Biology
Topic 1: Molecules, transport and health
The amino acid does not affect the overall folding and coiling of
polypeptide chain and therefore have no effect on tertiary
Linked to 1A.5.
Proteins
structure.
The shape of the active site may not be changed (i.e. have no effect on the
shape of active site).
Code: WBI11/01
Paper1
1B.2. The role of the blood
ab
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October 2019
Dr
.N
ag
wa
n
&
Ni
ha
lG
17
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Topic 1: Molecules, transport and health
ag
wa
n
&
Ni
ha
lG
ab
r
Biology
.N
The pressure of blood flowing through the artery will be low, so less
oxygenated blood (i.e. oxygen rich blood) will be delivered to body cells,
Dr
so insufficient oxygen delivered to cells, so less aerobic respiration,
which leads to breathlessness and lack of energy.
Dr.Nagwan Gabr& Dr. Nihal Gabr
119
Linked to
2A.6. The
mammalian
gas exchange
system
Topic 1: Molecules, transport and health
ab
r
Biology
lG
The events of the cardiac cycle becomes shorter and more frequent, as
Ni
ha
well as ventricles contract more forcefully during ventricular systole.
Dr
.N
ag
wa
n
&
1B.2. The role of the blood
The pressure exerted by one type of gas in a mixture of gases.
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Linked to
2.A.6.The
mammalia
n gas
exchange
system
Biology
Topic 1: Molecules, transport and health
Four subunits
Hemoglobin is a globular protein, having quaternary structure with four polypeptides, where each
polypeptide has a heam group (i.e. prosthetic group which is made up of Fe2+ and porpherin ring)
where each heam group binds to one oxygen molecule, so four heam groups bind to four oxygen
molecules. The binding of first oxygen molecule is difficult and causes conformational change
which increases the affinity of hemoglobin to oxygen, so the binding of the second, third and
fourth oxygen molecules become easier, the graph levels off as hemoglobin becomes saturated
lG
ab
r
with oxygen.
1B.3. Circulation in the blood vessels
Ni
ha
(7)b-
Arteries carry oxygenated blood from the heart under relatively high blood pressure whereas veins carry
blood to the heart under lower pressure. The pressure of blood drops in capillaries, due to their narrow
&
lumen as well as due to the exchange of substances that takes place between capillaries and respiring
cells, where at low PO2 in respiring cells, oxygen diffuses down its concentration gradient from the blood
Dr
.N
ag
wa
n
to body cells and carbon dioxide diffuses into blood.
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124
Metadata analysis
When data from all available studies are analyzed.
To give more reliable evidence.
•data quotes/data manipulation
When describing graphs (non-linear; i.e. no continuous increase or
decrease) or inconsistent.
Studies can be improved by
•Larger sample size
•Increased study time
•Use of controlled variables or control group.
Limitations of study include
•Small sample size
•Study carried in one country
•Followed only for x years
•Only one gender
•No information about other variables
•No control group
Important
1. Draw and plot error
bars.
2. Size of bar, the
longer the bar, the
more spread out data
is from the mean, so
the less reliable they
are and vise versa.
3. If error bars are
overlapping, then no
significant difference.
4 Water is the solvent for the transport of sodium chloride and glucose in the blood.
DO NOT WRITE IN THIS AREA
(a) The graph shows the effect of temperature on the solubility of sodium chloride
and glucose in water.
400
300
Solubility
/ g per 100 cm3 water
glucose
Exponential
200
Linear increase
sodium chloride
0
0
20
40
60
Temperature / °C
(i) Compare and contrast the effect of temperature on the solubilities of sodium
chloride and glucose in water.
(3)
DO NOT WRITE IN THIS AREA
100
Both show positive correlation, where as temperature increases, the solubility of
. . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. . . . . . . . . . . . . . . . . . . . . .
sodium chloride and glucose in water increases.
. . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. . . . . . . . . . . . . . . . . . . . . .
Yet, the initial solubility at 10C of both glucose and sodium were different as the
solubility of glucose was 75g per 100 cm3 while the solubility of sodium
. . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. . . . . . . . . . . . . . . . . . . . . .
Also, the rate of increase in solubility of glucose was higher than that of sodium
. . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. . . . . . . . . . . . . . . . . . . . . .
chloride as the solubility of glucose increases by almost 225g per 100 cm3
. . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. . . . . . . . . . . . . . . . . . . . . .
while the solubility of sodium chloride increased by only almost 10g per 100
. . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. . . . . . . . . . . . . . . . . . . . . .
cm3 with same increase in temperature.
. . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. . . . . . . . . . . . . . . . . . . . . .
Lastly, the increase in solubility if glucose was non-linear as the rate of increase
was low then increase gradually.
. . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. . . . . . . . . . . . . . . . . . . . . .
10
*P60516RA01028*
DO NOT WRITE IN THIS AREA
chloride was about 45g per 100 cm3.
. . . . . . . . . . . .. .. .. .. .. .. .. .. .. .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. . . . . . . . . . . . . . . . . . . . . .
Biology
1
Topic 1: Molecules, transport and health
(1C) Cardiovascular health and risk
January 2013
Code: 6BI01/01
Paper 1
1C.3. Risk factors for cardiovascular disease
Glucose is needed for
respiration, to provide energy
for the contraction of the
heart muscle.
Also, to maintain osmotic
ab
r
effect.
lG
Fastest heart rate
ag
wa
n
&
Ni
ha
Heart rate is above base rate
Dr
.N
0.1
Vitamin C is important for the formation of connective tissue in the body such as bones and,
teeth, skin and endothelial lining of blood vessels.
•So lack of vitamin C, increases the risk of damage of endothelial lining of arteries
•So arteries are more likely to be damaged
•So atherosclerosis more likely to develop
•So person is more likely to be affected by CVDs.
Dr.Nagwan Gabr& Dr. Nihal Gabr
126
Biology
Topic 1: Molecules, transport and health
Glucose is needed for aerobic respiration to provide energy for the contraction of the heart muscle.
Also, to maintain the osmotic pressure for no net movement of water between muscle cells and the
solution.
Validity is about controlled variables
lG
ab
r
Solutions were of same volume, also the concentration of glucose in all the solutions are the same.
Ni
ha
By repeating the experiment in all concentrations of caffeine.
Dr
.N
ag
wa
n
&
As the concentration of caffeine was increased from 0 to 0.1, the heart rate increased by 20%. As the
•0.1mg/cm3 causes
concentration of caffeine was increased above 0.1, the heart rate decreases.
Unethical to kill chicken embryos.
Dr.Nagwan Gabr& Dr. Nihal Gabr
127
fastest heart rate.
Topic 1: Molecules, transport and health
Ni
ha
lG
ab
r
Biology
&
Causes of decrease in risk factor
•Improvements in education (increased public awareness/knowledge/literacy)
ag
wa
n
•Improvements in healthcare (diagnosis, medication and treatment ex. statins)
Dr
.N
•Improvements in lifestyle (more exercise/improved diet/quitting smoking)
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130
Biology
2
Topic 1: Molecules, transport and health
January 2014
In addition to
increase in blood
Code: WBI01/01
Paper 1
1C.4. Diet and cardiovascular health
cholesterol level, so
more accumulation of
cholesterol on the
•Creates an energy imbalance, where the energy intake (i.e. fat intake) is greater than energy output
(i.e. fat burned).
•Obesity increases the risk of type 2 diabetes.
ab
r
•Which results in gain in weight that might lead to obesity. Where obesity is precursor to CVDs.
•Also, it leads to increase in blood pressure, where high blood pressure causes damage to the
lG
endothelial cells lining walls of artery, which stimulates an inflammatory response, where WBCs
accumulate at the site of damage.
Ni
ha
•Causing the buildup of cholesterol on the lining of arteries resulting in the formation of atheroma.
•Calcium salts and fibrous tissue build up around the atheroma, turning it into hardened plaque.
•Plaque causes narrowing of arterial lumen as well as loss of elasticity of arteries which causes
increase in blood pressure, that causes further damage resulting in atherosclerosis that leads to CVDs.
&
•That in turn results in heart diseases, stroke, heart attack (myocardial infarction) etc.
.N
(5)
ag
wa
n
1C. 2. Investigating the causes of CVDs
Dr
walls of arteries.
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131
Biology
Note that, three risk factors are needed to
Topic 1: Molecules, transport and health
improve diagnostic accuracy.
The higher the number of risk factors, the higher the relative risk of developing
CVD. Also, as the number of risks increases from 2 to 3 the relative risk of
CVD doubles.
(5) b-
Reduce salt intake
Increase Vitamin C consumption
•Statins
•Plant stanols
Ni
ha
Reduce alcohol consumption (no alcohol)
lG
ab
r
1C. 4. Diet and cardiovascular health
•Less energy intake
1C. 7. The treatment & risks of treatment
Dr
.N
ag
wa
n
&
(5)
Loss of excess salts and fluid in urine due to decreasing water reabsorption in
kidneys, thus reducing the volume of the blood which in turn causes reduction in
blood pressure which reduces the risk of atherosclerosis accompanied by a
reduction in the risk of CVDs.
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132
Biology
May 2014
Code: WBI01/01
1C.2.Investigation of the cause of CVDs
Paper 1
Ni
ha
lG
ab
r
3
Topic 1: Molecules, transport and health
ag
wa
n
&
Important
As different countries have different populations, so to allow standardization
Dr
.N
as well as valid comparison.
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133
Topic 1: Molecules, transport and health
lG
ab
r
Biology
Ni
ha
People are more aware about the risk factors of CVDs in Spain than in countries with higher death rate like
Ukraine. As well as there is better health care, diagnosis and medications (such as diuretics and statins) in
countries with lower death rate. In general, the lower the death rate due to CVDs the better people’s lifestyle
(ex. Less or no smoking/ less energy intake/ less saturated fat intake).
Less consistent
Dr
.N
ag
wa
n
&
1C.3. Risk factors for cardiovascular disease
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134
Biology
Topic 1: Molecules, transport and health
High blood pressure, causes damage to the endothelial lining of blood vessels,
which stimulates an inflammatory response, where WBCs accumulate at the
site of damage and cause building up of chemicals in blood as cholesterol.
Calcium salts and fibrous tissue build up around the atheroma turning it into
hardened plaque. Thus narrowing the diameter of the arterial lumen as well as
ab
r
causing loss of elasticity of lumen, which leads to atherosclerosis that in turn
causes further damage and can lead to heart diseases, angina, heart attack
Reduced blood supply to cells
lG
(myocardial infarction).
1C.7. The benefit & risk of treatment
ag
wa
n
&
Ni
ha
(4)
Dr
.N
1C.3. Risk factors for cardiovascular disease
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Topic 1: Molecules, transport and health
Ni
ha
lG
ab
r
Biology
1C.1. Risk, correlation & cause
(7) Important
&
•Using more students (larger sample size)
Dr
.N
ag
wa
n
•Repeating the investigation on each student.
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141
Biology
Topic 1: Molecules, transport and health
1C.7. The benefits & risks of treatment
Statins inhibit the synthesis of cholesterol in the liver, which reduces the
ratio of LDL to HDL, that in turn reduces blood cholesterol level, which
lowers the risk of formation of atheroma, so no plaque formed so tissues
thus reducing the risk of CVDs.
ag
wa
n
&
Ni
ha
lG
(3)
ab
r
are not deprived of oxygen and nutrients (i.e. no reduced blood flow),
Dr
.N
1C.5. Dietary antioxidant & cardiovascular disease
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144
Topic 1: Molecules, transport and health
.N
ag
wa
n
&
Ni
ha
lG
ab
r
Biology
Dr
Boiling increases membrane permeability to vitamin C, as
upon increase in temperature, transport proteins within the
membrane will denature. This results in the movement of
vitamin C through cell membrane by diffusion down its
concentration gradient, thus lowering the vitamin C content
in broccoli.
Dr.Nagwan Gabr& Dr. Nihal Gabr
146
Linked to 1C.1.
Risk,
correlation &
cause
Biology
Topic 1: Molecules, transport and health
.N
ag
wa
n
&
Ni
ha
lG
ab
r
1C.1 Risk, correlation & cause & 1C.4. Diet & cardiovascular health
Dr
Important
Probability of an event taking place in one group compared to another.
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147
Topic 1: Molecules, transport and health
ag
wa
n
&
Ni
ha
lG
ab
r
Biology
•Include females
.N
•People should be of same age
Linked to 1C.1.
Risk, correlation
& cause
Dr
•Larger sample size
•Allow recovery time
•Increased study time
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150
Biology
8
Topic 1: Molecules, transport and health
January 2017
Code: WBI01/01
Paper 1
1C.3. Risk factors for cardiovascular disease
(2)
Atherosclerosis can result in formation of atheroma/plaque in coronary arteries
(supplying the heart muscle with oxygen and nutrients), thus narrowing coronary
Ni
ha
•Formation of clot/thickening of artery wall.
lG
of oxygen and nutrients, resulting in CHD.
ab
r
arteries so reducing blood flow to the heart muscle, which deprives the heart muscle
1C.7. The benefits & risks of treatment
Dr
.N
ag
wa
n
&
(2)
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Biology
9
Topic 1: Molecules, transport and health
May 2017
Code: WBI01/01
1C.6. Using the evidence
Paper 1
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.N
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n
&
Ni
ha
lG
ab
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(3)
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Biology
Topic 1: Molecules, transport and health
Important
•Lower blood pressure
•Lower blood cholesterol level (lower LDL to HDL ratio)
•Lower BMI (less body fat)
•Cardiac/heart muscle is stronger (training increases the strength of heart
muscle).
lG
ab
r
•Low heart rate.
1C.4. Diet and cardiovascular health
Dr
.N
ag
wa
n
&
Ni
ha
(4)
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154
Biology
Topic 1: Molecules, transport and health
1C.4. Diet & cardiovascular health
(5) b-
BMI might not be a reliable indicator for the risk of CVD in people with high muscle mass such
as athletes as it cannot differentiate between muscles and fat.
Could lead to older people who have lost most of their muscle mass to underestimate the risk
of CVD.
ab
r
Lack of education about the fact that high BMI is a risk factor for CVD.
October 2018
Code: WBI01/01
Paper 1
1C.7. The benefits & risks of treatment
Ni
ha
12
lG
Also, people having high BMI don’t show symptoms of CVD.
Dr
.N
ag
wa
n
&
(2)
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Biology
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Topic 1: Molecules, transport and health
January 2019
Code: WBI01/01
Paper 1
1C.7. The benefits & risks of treatment
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(3)
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Antihypertensives (including diuretics, beta blockers, sympathetic nerve
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inhibitors-ACE inhibitors)/statins.
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Biology
Topic 1: Molecules, transport and health
1C.7. The benefits & risks of treatment
(2)
Thrombin is an active enzyme, that catalyses the conversion of the soluble,
globular protein fibrinogen into the insoluble, fibrous protein fibrin. Where
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anticoagulant, prevents binding of thrombin to fibrinogen, so no enzyme substrate
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complex, so no fibrin formed, so no mesh is formed so blood does not clot.
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•Platelets become less sticky, and so won’t be able to bind to each other or to
fibrin.
•So no mesh/clot would be formed.
•Also, thromboplastin would not be released so the blood clotting cascade of
reactions is not stimulated.
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Biology
Topic 1: Molecules, transport and health
Fibrin, is an insoluble fibrous protein that forms fibrous mesh,
trapping blood cells and platelets to form a clot. Where plasmin,
Linked to 1B.2.
The role of the
blood
cause the hydrolyses of fibrin, thus breaking down peptide bond
between amino acids in fibrin. So no mesh formed, so blood does
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not clot.
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1C.5. Dietary antioxidant & cardiovascular disease
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Dietary antioxidants, donate electrons, reducing free radicals (toxins) thus
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preventing the oxidation of other molecules, and therefore reducing the risk
of damage of endothelial lining, reducing plaque/atheroma formation, which
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in turn reduces the risk of atherosclerosis and CVDs.
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Topic 1: Molecules, transport and health
1C.3.Risk factors of CVD
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2.
The 10 Year CHD Risk would increase, as smoking is a risk factor that
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contribute to CVD. Where it contains nicotine that raises blood pressure and
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causes formation of atheroma/ plaque on the arterial lining as a result of
inflammatory response, which leads to atherosclerosis and increases the
risk of other CVDs.
Increase in heart rate thus making the heart work harder.
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Topic 1: Molecules, transport and health
BMI/ obesity/ waist to hip ratio
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As BMI increases the value for the 10 year CHD risk increases.
If someone has high BMI yet does not smoke, this might lead to them
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underestimating the risk of high BMI on CVD as the value obtained for the
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10 year CHD risk will be lower.
Also, might lead to person underestimating how much they smoke.
In addition, the blood cholesterol level and blood pressure might be an
estimate.
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Other risk factors not included.
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Topic 1: Molecules, transport and health
1C.3. Risk factors for CVD
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•Energy imbalance leads to obesity
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(5) C-
•High LDL levels leads to damage to the endothelial lining of arteries
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•Inflammatory response
•Leads to formation of atheroma/plaque causing atherosclerosis
•Leads to loss of elasticity + narrowing of lumen of artery
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•Reduced blood flow to heart
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•Causing reduced amount of oxygen to reach the heart/ tissues.
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Biology
Topic 1: Molecules, transport and health
Important
January 2020
Code: WBI11/01
Paper1
1C.4. Diet and cardiovascular health
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High salt intake increases the hazard ratio for all causes of death.
High salt intake has greatest effect on CAD where it caused the most increase in
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hazard ratio.
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Topic 1: Molecules, transport and health
1C.3. Risk factors of CVD
(6)
•Both age and smoking increase the hazard ratio.
•As smoking increases heart rate and blood pressure, as well as with increasing age
arteries lose part of their elasticity.
BMI
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Blood pressure
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•Therefore, study would not be valid without controlling both factors.
Blood cholesterol levels/LDL to HDL ratio
Exercise levels
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Obesity
Gender
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Type 2 diabetes
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Topic 1: Molecules, transport and health
1C.4. Diet and cardiovascular health
(6)
To allow valid comparison between the effect of high salt intake and low salt intake
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on the hazard ratio for different causes of death.
The tendency of two sets of data to increase together, where an increase in one
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variable is accompanied by an increase in another variable.
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•Difficult/impossible to control all variables/risk factors.
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•No clear definition of low/high salt intake.
How blood clots form in a blood vessel.
•Collagen is exposed when walls of blood vessel is damaged
•Contact between collagen and platelets cause the activation of platelets where they
break down in large numbers releasing serotonin and thromboplastin.
•Thromboplastin catalyzes the conversion of prothrombin into thrombin.
•Thrombin then catalyses the conversion of fibrinogen into fibrin.
•Fibrin forms a mesh trapping blood cells and platelets forming a clot.
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Building a model of cell membrane (showing how technical developments
overtime lead to better/enabled better scientific understanding)
•Lipid soluble substances could diffuse through cell membrane more easily
than other substances, indicating that large part of the membrane structure
must be lipid.
•When punctured with a needle, the cell membrane sealed again showing that
cell membrane is fluid.
•A device was developed to collect monolayers.
•The total size of monolayer film formed by lipids extracted from human
RBCs was measured.
•Scientists estimated the total surface area of a red blood cell.
•Where it was found that their measured area of monolayer was about twice
the estimated surface area of cell, so they reached the conclusion that cell
membrane is a lipid bilayer.
•Yet, the results were wrong in two ways, where the devise used did not extract
all the lipid molecules (so measured area of monolayer was lower than actual)
in addition to that, they miscalculated the surface area of human red blood cell
as they thought cell was flat rather than biconcave (so the estimated surface
area of RBC was lower than actual).
•Yet, the conclusion was correct as the two errors cancelled each other.
•Modern techniques using X-rays and electron microscopy methods showed
more details of lipid bilayer (i.e. showing fluid mosaic model of cell membrane).
Active transport
•An active process that requires energy from the hydrolysis of ATP, where energy is needed for
change in shape of carrier protein.
•It is the movement of polar molecules or ions through carrier proteins in cell membrane, due to the
hydrophilic amino acids lining channels.
•Where these polar molecules or ions have complimentary shape to the binding site of protein
carriers in cell membrane, so they fit and bind with these carriers causing conformational change
in the shape of carrier proteins using ATP allowing specific polar molecule or ion to pass against
their concentration gradient.
•Protein carriers can then return passively to their original shape to allow more molecules or ions
to enter the cell.
Evidence of active transport
•Occurs in living cells only.
•Cells have high numbers of mitochondria.
•Respiratory poison stops it.
Factors affecting active transport
•Oxygen and glucose concentration
•Number of protein carriers
•Number of mitochondria
•Presence of respiratory poisons
Note that, ATPase is an enzyme that catalyses the hydrolysis of ATP into ADP and phosphate,
releasing energy to move carrier systems and drive metabolic reactions.
Canine is a metabolic poison that stops mitochondria working.
Differences between active transport and facilitated diffusion
•Active transport requires energy from ATP, whereas facilitated diffusion doesn’t require energy
(i.e. it is a passive process that depends on kinetic energy of molecules).
•Active transport involves the movement of polar molecules and ions against their concentration
gradient, while in facilitated diffusion molecules move down their concentration gradient.
•Active transport uses only carrier proteins, while facilitated diffusion uses both carrier proteins
and channels (pores).
•Active transport involves co-transport while facilitated diffusion does not involve co-transport.
Compare and contrast diffusion and active transport marking scheme answer:
Similarities
•both move molecules through the {phospholipid bilayer / cell surface membrane}
•(in both) molecules can move through proteins
Differences
•diffusion occurs down a concentration gradient whereas active transport occurs
against a concentration gradient
•diffusion is {passive / does not require ATP} whereas active transport requires
ATP
Bulk transport
Involves the transport of large molecules such as proteins, polysaccharides, parts of cells or even
whole cells where this requires energy and is a form of active transport.
Endocytosis and exocytosis
Endocytosis
•involves engulfing of material by cell surface membrane to form a sac or endocytotic vacuole,
using energy from ATP.
•involves substances entering the cell.
•involves the formation of vesicles from the cell surface membrane.
Exocytosis
•Process by which materials are removed from cell (involves substances leaving the cell).
•Involves fusion of vesicle with cell surface membrane.
Both endocytosis and exocytosis involves vesicles and involves the use of energy from ATP.
Compare and contrast endocytosis and exocytosis marking scheme answer:
•they both involve formation of a vesicle
•both require ATP (are active processes)
•endocytosis takes substances into the cell and exocytosis removes substances from the cell.
Gas exchange in small organisms
+they have low metabolic rate (i.e. low energy demand).
Single celled organisms and very small multicellular organisms have a large surface area to volume ratio.
This means they can get oxygen they need for cellular respiration from air or water they live in through their outer body
Note that the surfaces of small organisms are
surface by diffusion, which would be sufficient to supply their needs.
Gas exchange in large organisms
Why is circulatory system required in gas exchange?
permeable to gases allowing diffusion of gases
through membrane.
As diffusion of gases over surface is not enough
So, larger organisms need to have a mass transport system/circulatory system
Heart
To generate pressure, ensuring mass flow (which is the transport of substances from high pressure to low pressure over a
long distance). Thus overcoming limitation of diffusion, where they have small surface area to volume ratio, so longer
distances for nutrients to reach cells, and they have high metabolic rate therefore, diffusion alone would be too slow and
insufficient.
System of branching vessels
That carry substances, following a very specific route to required body parts.
Capillaries which ensure large surface area for gas exchange, thin wall for shorter diffusion distance.
Suitable transport medium (blood)
In which oxygen , nutrients, as well as waste products dissolve.
Fick’s law of diffusion
Rate of diffusion=
(surface area x concentration gradient)/thickness of exchange membrane or barriers (exchange surface)
Properties of gas exchange surfaces/factors affecting rate of diffusion of gases across a membrane,
•The surface area where the larger the surface area , the more particles can be exchanged at the same time.
•The concentration gradient of particles diffusing, by maintaining the concentration gradient (ex by transporting substances
away once they have diffused by continuous blood flow, ventilation).
•The thickness of the exchange surfaces, where the shorter the diffusion distance , the faster the diffusion can take place.
The mammalian gas exchange system
Features of effective gas exchange system
•A large surface area to compensate for the relatively small surface area to volume ratio of the whole organism.
•Thin layers to minimize the diffusion distance from one side to another.
•Continuous blood flow/supply to the respiratory surfaces as in animals, maintaining steep concentration gradient.
•Moist surface because diffusion takes place with the gases in solution.
•Permeable surfaces that allow free passage of the respiratory gases.
How the structure of human lungs is adapted for efficient gas exchange?
•Many alveoli, so large surface area.
•Covered by extensive network of capillaries, which ensures large surface area for gas exchange.
•Thin capillary walls as well as alveolar walls as their walls are made from single layer of flattened cells so, shorter diffusion
distance, allowing faster diffusion.
•Maintaining steep concentration gradient by ventilation and continuous blood flow.
Human gas exchange system
Nasal passage
•Warm, clean and add moisture to the air.
Pharynx
•Common pathway for food and air (epiglottis closes trachea during swallowing which is an involuntary
reflex action).
Epiglottis
•Stops food getting into lungs when swallowing.
Larynx (vocal box)
•Contains the vocal cords, uses flow of air across it to produce sounds.
Trachea
•Tube with incomplete rings of cartilage, which keeps it open and prevents it from collapse and allow
continuous flow of air into lungs. Trachea carries air to lungs, lined with goblet cells making mucus, and
cells with cilia (ciliated epithelial cells) which move mucus away from the lungs.
Note that, the incomplete rings of cartilage allows the food to be swallowed and moved down oesophagus.
Left and right bronchi
•These tubes lead to the lungs and are similar in structure to trachea but narrower. They divide to from
bronchioles.
+with complete rings of cartilage
Bronchioles
•Small tubes that spread through the lungs and end in alveoli. Their main function is still as an airway, but
some gas exchange can take place.
Pleural membrane
•Surround the lungs and line the chest cavity forming a sterile sealed unit.
Pleural cavity
•Space between the pleural membranes, usually filled with a thin layer of lubricating fluid that allows the
membrane to slide easily with breathing movements.
Alveoli
•Site of gas exchange (thin walled, large surface area, moist, rich in blood supply and well ventilated)
Diaphragm
•A muscle sheet separating the chest cavity (thorax) from the abdominal cavity.
It is dome shaped, with a fibrous middle part forming the roof of the dome, and muscular edges forming
walls. It is flat in the contracting state.
Internal intercostal muscles
•Pulls ribs down and in during exhalation
External intercostal muscles Contracts during inspiration as it is an active process.
•Pulls ribs up and out during inhalation
Cartilage
Found in trachea and bronchi.
Function
•Give support to the walls of the trachea and bronchi.
•Prevents them from collapse as during inhalation the pressure inside the airways falls and the cartilage stop
them collapsing
•Keep air way open and air resistance low.
In trachea, it is C-shaped rings.
In bronchi and large bronchioles, irregular blocks of cartilage.
Goblet cells
Found in trachea and bronchi seen in the ciliated epithelium lining.
Mucus is contained in secretory vesicles and released by exocytosis.
Function
•Secrete mucus on surface of ciliated epithelium, which is sticky to trap particles of dust, pollen and bacteria.
•So pathogens don’t reach the cells lining the trachea/bronchi/alveoli, thus reducing chance of infection.
In case of infection, there is an increase in secretions of mucus.
Ciliated epithelium
Found in trachea and bronchi and in larger bronchioles.
Function
•Cilia beats back and forth
•Waft (move) mucus that has trapped dust and bacteria towards back of the throat, where mucus will be
swallowed, so any present bacteria will be destroyed by stomach acid.
•Thus allowing normal air flow while keeping air ways clean, preventing bacteria from entering lungs.
•So reducing risk of infection.
How gases are exchanged in the lungs (alveolus)
Gas exchange takes place between alveoli and blood in blood capillaries, where alveolar air
has a higher concentration of oxygen and a lower concentration of carbon dioxide than
blood in capillaries.
High PO2 and low PCO2
Oxygen therefore, diffuse from the air in the alveoli, across the walls of the alveolus and
capillary and enters the blood .
Carbon dioxide diffuses in the opposite direction.
Where the diffusion gradients are maintained by,
•Continuous blood flow past the alveolus, which brings deoxygenated blood from the
pulmonary artery and takes away the oxygenated blood through the pulmonary vein
(circulating blood supply).
•Ventilation of the lungs, which replace alveolar air with air from outside the body (removal
of carbon dioxide and replenishment of oxygen).
How alveoli are adapted for gaseous exchange
1. Thin alveolar wall (squamous epithelium)
Providing short distance of diffusion of gases (gas exchange) between air in alveolus and blood in
capillary which speed up the rate of diffusion of gases.
2. Many alveoli
Providing larger surface area for diffusion (gas exchange), where larger number of molecules (carbon
dioxide and oxygen) can diffuse at the same time.
3. Surrounded by many capillaries (extensive capillary network)
•Capillaries are very close to the alveoli, in other words very little distance between alveolar epithelium
and capillary endothelium for faster rate of diffusion.
•The walls of the capillary (endothelium) is one cell thick for short distance of diffusion as well.
•The continuous flow of blood in blood capillaries maintain steep concentration gradient.
•Form a large network which increase surface area to slow down the rate of flow of blood in capillaries,
for more efficient gas exchange.
4. Surfactant secreting cells
These are special, large rounded cells between squamous epithelial cells in the alveolar walls, secreting
pulmonary surfactant (complex of phospholipids and proteins)
•Which reduces surface tension inside the alveoli, keeping the alveolar walls from collapsing as they
deflate during exhalation.
•Help dissolve oxygen to diffuse into blood.
Why air reaching lungs doesn’t cause infection.
•Sticky mucus produced by goblet cells and mucous glands traps dust and bacteria thus prevent bacteria
from causing infections of gas exchange and prevent them from reaching blood (mucus acting as a
barrier).
•Cilia on ciliated epithelial cells beats back and forth moving mucus carrying dust and bacteria out of
lungs.
•Macrophage that protect lung by preventing the pathogen entering the blood , by engulfing inhaled
particles and bacteria and digesting them by phagocytosis.
Breathing (ventilation) is an active process
Inhalation (inspiration)
•Inhalation is an active process, where external intercostal muscles contract, moving the
ribcage up and out.
•Diaphragm contracts moving down (flattened).
•Volume of the thoracic cavity increases.
•Pressure of air in lungs decreases, with higher pressure of air outside the lungs. So, air is
forced into the lungs.
Exhalation (expiration)
•Normal exhalation is a passive process, where external intercostal muscles relax, ribcage falls
down under gravity.
•In forced exhalation, where internal intercostal muscles contract and pull the ribcage down
and in.
•Diaphragm relaxes moving up (dome shaped).
•Volume of the thoracic cavity decreases.
•Internal pressure in lungs increases, so air is forced out of the lungs.
Note that, exhalation is helped by the fact that the lungs are elastic, so they tend to empty like a
balloon.
Role of respiratory system in gas exchange
•Ventilation involves removal of carbon dioxide and bringing of oxygen, thus maintaining steep
concentration gradient.
•Alveoli which has the adaptations including, large surface area, surfactant, thin wall, rich in blood
capillaries.
•This allows overcoming the limitation of diffusion (small surface area to volume ratio, long diffusion
distance, high metabolism and concentration gradient)
How concentration gradient maintained through gas exchange surface in human lungs
Ventilation
•Removing carbon dioxide and replenishing oxygen
Blood flow in capillaries (i.e. continuous blood flow)
•Removing oxygenated blood (oxygen) away from alveoli and bringing carbon dioxide to the
alveoli.
Breathing (ventilation)
•The process in which physical movement of the chest changes the pressure so that air is moved in
or out aided by diaphragm and intercostal muscles
Biology
1
Topic 2: Membranes, proteins, DNA and Gene Expression
January 2013
(2A) Membranes and transport
Code: 6BI01/01
Paper 1
2A.1 Cell membranes
The cell membrane is extremely thin, about 7nm thick. It is composed of a
phospholipid bilayer with polar head and non polar tail. The hydrophilic phosphate
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heads lie facing watery solutions on the inside and outside of cell membrane (i.e.
cytoplasm/cytosol and tissue fluid, whereas the hydrophobic tails are repelled
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away from water forming hydrophobic core that is impermeable to hydrophilic
substances. There are protein molecules embedded within the phospholipid bilayer
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(intrinsic/integral proteins) including transport proteins (carrier/pores and
channel proteins), as well as there are glycoproteins, cholesterol and glycolipids.
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2A.3. Osmosis
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Marking scheme points
•Phospholipid bilayer
•Description of phospholipids
(eg: phospholipids are fluid).
•Proteins
•Transmembrane proteins
(intrinsic/integral proteins)
•Glycoproteins, glycolipids and
cholesterol.
Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
Phospholipid bilayer form the basic structure of cell membrane. Where phospholipids are
composed of hydrophilic (polar) phosphate heads that lie facing aqueous solutions on the
outside of the membrane (cytoplasm and tissue fluid) while hydrophobic (non polar) fatty
acid tails are repelled away form water and aggregate together forming hydrophobic core,
that is impermeable to hydrophilic substances. Phospholipids are fluid, where they can
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diffuse within their monolayer, giving the membrane a flexible structure that is constantly
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changing in shape. Proteins are found within the phospholipid bilayer where that interact
with phospholipids, such that the hydrophilic R groups interact with phosphate heads and
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hydrophobic R groups interact with fatty acid tails.
2A.3. Osmosis
(3)
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Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
2A.1. Cell membranes
Phospholipid molecules are composed of hydrophilic phosphate head and
hydrophobic fatty acid tails, where polar heads lie facing watery solutions on both
sides of the cell membrane as they are water soluble and form hydrogen bonds with
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water thus helping to stabilize the cell membrane, while non polar fatty acid tails are
impermeable to hydrophilic substances.
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repelled away from water forming hydrophobic core, i.e. forming a layer that is
Fatty acid tails are hydrophobic, they aggregate together and orientate away from water. Where phosphate groups on the
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phospholipid are hydrophilic and associate with water. Two phospholipid monolayers form bilayer.
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Cell membrane is fluid, where protein molecules and phospholipids can
move/diffuse within their monolayer, giving the membrane a flexible
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structure that is constantly changing in shape.
Mosaic, where there are protein molecules scattered within the
phospholipid bilayer, including pores/channel and carrier systems in
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lipid bilayer.
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Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
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Hydrocarbon tails
0.4
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Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
15.38
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Negative correlation
Cholesterol reduces membrane fluidity where it forms hydrophobic interaction
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with fatty acid tails of phospholipids, thus bringing them closer together so less
movement is possible.
Combines with fatty acid tails, holding/pulling them closer together, reducing
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movement of phospholipids/fatty acids.
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Topic 2: Membranes, proteins, DNA and Gene Expression
May 2017
Code: WBI01/01
2A.1. Cell membranes
Paper 1
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Biology
Phospholipid molecule
Important
•Phospholipids form bilayer, as they have polar heads and non-polar tails.
•Proteins are located between the phospholipids.
•Due to the interaction between R groups of proteins and phospholipids.
•Phospholipids are free to move, making the membrane fluid.
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Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
Platelets are activated
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2A.2. Cell transport & diffusion
9:1
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Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
•No effect on the total membrane phospholipids
•The inner layer will have a relatively higher content of the other
•Will alter membrane permeability
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phospholipids.
Linked to
1A.1. Cell
membranes
•So that platelets will release thromboplastin
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•Thromboplastin is an enzyme
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•Catalyses the conversion of prothrombin into thrombin
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Linked to 1B.2.
Role of the blood
& 2B.1. Enzymes
Topic 2: Membranes, proteins, DNA and Gene Expression
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Biology
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2A.1. Cell membrane
Cell membrane is fluid where phospholipid molecules can move about/diffuse within
their monolayer, giving the membrane a flexible structure that is constantly changing
in shape.
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Presence of cholesterol contributes to fluidity.
Would increase the surface area of cell membrane so the uptake of substances
would be faster.
Linked to 2A.2. Cell
transport & diffusion
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Enzymes
When describing graph
•positive/negative correlation
•linear/non linear
Note that, when increasing the surface area to volume ratio of substrate,
more surface is exposed, so more frequent successful collisions between
enzyme and substrate, so more enzyme substrate complex, so higher rate of
reaction.
Why enzyme can break substrate quickly
Why initial rate is measured
Effect of enzyme concentration on rate of reaction
As enzyme concentration increases, more number of active sites, so
more frequent successful collisions between enzyme and substrate, so
more enzyme substrate complexes formed, so higher rate of reaction.
Mechanism of action of enzymes
•enzymes have a specific active site
•substrate has a complimentary shape to the active site
•substrate fits and binds to active site by temporary hydrogen bonds
•forming enzyme substrate complex
•causing strain (i.e. stress on substrate)
•so lowers the activation energy (i.e. reaction takes place at lower temperature)
•products produced no longer fit into active site, so they will be released
•enzyme is free to bind to another substrate, where it is not used up in the
reaction.
How enzymes work by induced fit mechanism
•the substrate is partially complimentary to the active site
•active site changes shape slightly when substrate fits to it.
•i.e. it molds and folds around substrate.
•so active site and substrate are now complimentary and better fit.
•allowing formation of enzyme substrate complex.
•where R groups of the amino acids in the active site interact with substrate, so
strong bonding of substrate to active site.
•this interaction cause the break of substrate apart or encourage the formation
of new bonds between molecules, forming one, two or more bonds.
Activation energy is the energy needed by the reactants to reach the
unstable transition state to be converted into products.
How enzymes lower the activation energy
•by providing an alternative pathway for the reaction to take place.
•bring reactants close together in the active site forming enzyme substrate
complex.
•where R groups of amino acids in the active site interact with the reactants
(i.e. substrate)
•thus making it easier for bonds in the reactant (substrate) to break down or
formed to form products.
Investigating the progress of an enzyme catalyzed reaction
•start with known concentration of substrate and enzyme.
•set controlled variables (temperature and pH)
•measure rate of decrease in substrate concentration or increase in product
concentration.
If the independent variable is enzyme concentration
•initially, high concentration of substrate due to the presence of free active sites
so more enzyme substrate complexes formed, so higher rate of reaction.
•rate slows down as concentration of substrate decreases (i.e. more substrate
converted into products), less substrate to bind with enzymes, so less occupied
active sites, so less number of successful collisions so less enzyme substrate
complexes formed so slower rate of reaction by time until reaction stops and
graph levels off (i.e. all substrate used up).
•Initial rate measured by calculating slope of graph as close to time zero as
possible
In order to have a fair and valid comparison, the initial rate of reaction is
compared as initially the substrate concentration is highest (i.e. it is not a
limiting factor), so highest chance of collisions between enzyme and
substrate, so highest possible rate of reaction.
But once the reaction proceeds, the substrate concentration decreases with
different rates, till the rate eventually levels off.
Molecular activity/turnover number is the maximum number of substrate molecules
upon which an enzyme can act and turn into products per unit time.
Hint
•In the prothrombin question, the structure of prothrombin is altered so when changed
into the active enzyme thrombin by the action of thromboplastin, thrombin has higher
molecular activity thus causing increase in the formation of blood clots.
Temperature and enzyme activity
Temperature coefficient (the measure of effect or temperature on reaction rate)
Q10= rate of reaction at (X+10C)/rate of reaction at XC
Below optimum
•increase in temperature increase the kinetic energy of enzyme and substrate.
•so molecules move faster.
•so more frequent successful collisions between enzyme and substrate.
•so more enzyme substrate complexes formed
At optimum
•enzyme works at its best
Above optimum
•rate of reaction decreases steeply
•molecules vibrate so energetically that some of the bonds holding the enzyme
molecule in its precise shape gets broken down (mainly hydrogen bonds)
•so enzyme loses its tertiary structure.
•the shape of the active site changes and 3D shape of enzyme changes.
•enzyme denatures (i.e. inactive)
Thermophilic bacteria living in hot springs can work at very high temperatures.
•they have temperature resistant proteins that contain a very high density of
hydrogen and disulfide bonds, which hold them together even at high
temperatures.
As temperature decreases below optimum, enzyme deactivation occurs, by loosing
their kinetic energy, so decreasing collisions thus decreasing rate of reaction.
Substrate concentration
At low substrate concentration
•substrate is a limiting factor
•there are few collisions between enzyme and substrate
•some active sites are occupied (becomes more occupied by increasing substrate concentration).
•so few enzyme substrate complexes formed
At higher concentration of substrate (after reaching Vmax-i.e. saturation level where all active sites are occupied)
•enzyme concentration is a limiting factor (where at this point, only an increase in enzyme concentration will
increase the reaction rate).
•all active sites are occupied
•maximum number of active sites formed
•so further increase in substrate concentration doesn’t increase the rate of reaction.
pH and enzyme activity
•changing pH changes the concentration of hydrogen ions in solution.
•the charges on R groups of amino acids at the active site may be affected.
•so ionic bonds maintaining the shape of tertiary structure breaks.
•so shape of the active site is altered and enzyme denatures
•so no enzyme substrate complex as substrate is no longer complimentary
to enzyme.
Comparing enzyme affinity to substrate
Turnover/molecular activity is the maximum number of substrate upon which
enzyme molecule can act and change into product per minute.
Vmax is the maximum rate of enzyme catalyzed reaction, at the Vmax all
active sites are occupied (i.e. saturated) with substrate.
Km is the affinity of enzyme to substrate (i.e. the substrate concentration
needed to reach half the Vmax)
As Km increases, affinity decreases.
Important
•Note that, in experiments use control as a reference to
set colorimeter absorbance to zero.
•if the cuvette is scratched it can result in greater
absorbance of light, yet this is a systematic error as it will
cause readings to be higher than true value for every
measurement.
•When measuring different pH, select buffer solutions for
the different pH values being investigated.
Mechanism of competitive inhibitors (used to control rate of enzyme catalyzed reaction)
•inhibitor has similar shape to substrate (i.e. complimentary shape to the active site of
enzyme)
•compete with substrate for the active site of enzyme
•binds to active site
•thus reducing frequency of successful collisions between enzyme and substrate.
•so fewer enzyme substrate complexes formed.
•so lower rate of reaction at lower substrate concentration. Yet has no effect at higher
substrate concentration.
Effect on Vmax and Km
Where at higher substrate concentration, the frequency of successful collisions increase, so
more enzyme substrate complexes formed so higher rate of reaction, thus cancelling the
effect of competitive inhibitor.
Vmax is determined by enzyme concentration, where upon increasing substrate
concentration, inhibitor has less effect and Vmax is reached, meaning that Km is higher
so reduced affinity of enzyme to substrate as inhibitor competes with enzyme on active
site. Vmax depends on the enzyme concentration, so competitive inhibitor has no effect on Vmax.
Non competitive inhibitor (reduce maximum rate of reaction i.e. Vmax)
•inhibitor binds to a site on enzyme other than active site such as allosteric site.
•causing a change in tertiary structure of enzyme
•causing a change in shape of active site as it disrupts the normal arrangement of
hydrogen bonds and hydrophobic interactions holding the enzyme molecule in its
3 dimensional shape.
•so substrate is unable to bind to active site
•so fewer enzyme substrate complexes formed thus reducing enzyme activity
•Vmax decreases as increasing substrate concentration will have no effect.
•Km stays constant as the inhibitor doesn’t interfere (i.e. compete) with the
binding of substrate with the enzyme.
Anabolic (building up of large molecules from smaller ones using energy from ATP)
Catabolic (breaking down of large molecules into smaller ones releasing energy)
Intracellular enzymes include DNA polymerase and are enzymes synthesized in
cell and operate within cells.
Extra cellular enzymes include digestive enzymes and are enzymes secreted by
cell and catalyze reactions outside cells.
Nucleic acids are made up of many nucleotides, held together by phosphodiester
bonds forming polynucleotides. DNA and RNA are polymers made from
monomers known as nucleotides, they are therefore polynucleotides.
Nucleotides are made up of three smaller components
•phosphate group (negatively charged)
•pentose sugar
•nitrogen containing base
These three units combine together by condensation reaction with elimination of
two water molecules to form a mononucleotide.
•base is either purine base (two
•phosphate
rings including, adenine and
group means
that nucleotides
are acidic and
are negatively
charged.
guanine) or pyrimidine base
(single ring including, thymine,
uracil and cytosine).
•pentose sugar (either deoxyribose or ribose), the difference
is that deoxyribose has one less oxygen atom in its molecule.
Adenosine triphosphate ATP
Structure
•it is a phosphorylated mono nucleotide, made from ribose (pentose sugar) and
adenine (nitrogen containing base), forming adenosine, and can be combined
with one, two or three phosphate groups to give, adenosine mono phosphate,
adenosine diphosphate and adenosine triphosphate.
Function
•ATP is a universal energy donor as it is small and water soluble so can easily
diffuse between cell organelles and is an immediate energy donor as it easily
hydrolyzed to ADP to release energy in presence of water.
•used in cell division, muscle contraction, maintenance of body temperature,
anabolic reactions such as protein synthesis and nerve impulse transmission.
Formation of polynucleotide
•formed during interphase, where many nucleotides
are linked together by
condensation reaction forming phosphodiester bond
between the phosphate of one nucleotide and carbon
3’ in the pentose sugar of the other nucleotide.
•the phosphodiester bond links the carbon 5’ of one
sugar with the carbon 3’ of the next forming sugar
phosphate backbone with its bases alongside (i.e.
pointing inwards from the two sugar phosphate
backbones in case of DNA)
The structure of DNA molecule
•the DNA molecule is composed of two polynucleotide strands, that are anti parallel
to each other (i.e. they run on the opposite direction, where the strand are 3’ to 5’
and 5’ to 3’)
•polynucleotide strands are made up of nucleotides which are composed of even
smaller molecules, including deoxyribose sugar, phosphate group and nitrogenous
base.
•the polynucleotide strands are held together by hydrogen bonds formed between
the nitrogenous bases (i.e. the amino and carboxyl groups of purine and pyrimidine
bases on the opposite strands).
•the bases pair together according to the complimentary base pairing rule where in
each base pair there is a purine and pyrimidine (i.e. A pairs with T and C pairs with
G)
•each strand has sugar phosphate backbone with phosphodiester bonds between
mono nucleotides.
•the two strands twist forming a double helix (3D shape).
•each full turn in a DNA molecule has 10 base pairs (3.4 nm in length).
Importance of hydrogen bonds between polynucleotide strands
•hydrogen bonds hold the polynucleotide strands together.
•they contribute to the 3D structure of DNA (where hydrogen bonds
between bases stabilize the a-helix structure)
•many hydrogen bonds give stability
•hydrogen bonds are more easily broken than covalent bonds therefore,
strands are easily separated for replication and transcription.
•hydrogen bonds are formed between specific bases so few mistakes (i.e.
faithful replication)
•hydrogen bonds can be easily reformed without chemical reaction.
Structural features of DNA making it a stable molecule
•complimentary base pairing holds the strands together.
•due to many hydrogen bonds holding strand together.
•sugar phosphate backbone with phosphodiester bonds.
•double helix structure protects bases.
•coiling protects from enzyme or any chemical attack.
Importance of genetic stability
•sequence won’t be spontaneously changed, thus decreasing chance of
mutation, so protein produced will always be functional.
•maintain all genetic information throughout the life of cell so that it can
be passed on to daughter cells.
•maintain size so that DNA stays enclosed within nucleus.
Semi conservative replication
An increase in the number of DNA molecules, where each DNA becomes
replicated (i.e. copied) where each old parental strand act as template strand to
form complimentary strand. Thus, producing two genetically identical molecules,
where the new DNA molecule has one old and one new strand.
Occurs during the S phase of the cell cycle (i.e. late interphase).
Steps of DNA replication
•the DNA double helix unwinds.
•hydrogen bonds between complimentary bases are broken down by the
enzyme, DNA helicase (strands separate).
•the free activated nucleotides line up along both strands.
•where both DNA strands act as templates, each in the bases of the
activated DNA nucleotides pair up with its complimentary base on each of
the old DNA strand where hydrogen bonds are formed between bases.
•DNA polymerase enzyme assembles the new nucleotides along the DNA
template strand step by step sequentially.
•DNA ligase enzyme catalyses the formation of phosphodiester bonds
between adjacent mono nucleotides.
•the process continues along the whole DNA molecule.
•producing two genetically identical DNA molecules.
•replication is semi conservative where each newly formed DNA molecule
has one old parental strand and one newly synthesized strand.
•where each of the two strands, the old and the new complimentary one
wind together forming two DNA helices that are genetically identical to
each other and to their mother.
Experimental evidence for semi conservative replication by Meselson and Stahl
•the bacteria (E.coli) were grown for many generations in a medium containing the
heavy isotope of nitrogen N15.
•this produced bacteria with heavy isotope, nitrogen 15 carried on both strands of
its DNA molecule, thus DNA would be heavier than the DNA with nitrogen 14.
•the bacteria with heavy isotope, nitrogen 15 strands on its DNA were grown in a
medium containing the normal isotope nitrogen 14, and were left to divide one
generation.
•the offsprings showed DNA molecule with both strands N14 N15.
•the second generation had N14 N14 and N15 N14.
Gene
A gene is a length of DNA containing a specific sequence of bases
that codes for specific sequence of amino acids to form specific
protein with particular characteristic/phenotype/feature.
Sense strand (non template strand)
The strand on the DNA molecule, that carries the code for the
manufacture of protein in a cell.
Anti sense strand (template strand)
Is the other strand on DNA molecule which is used to stabilize the DNA
and allow its replication. DNA strand which acts as a template for an
mRNA molecule
The sequence of three bases on template strand of the DNA
codes for one amino acid, the sequence of bases that codes for
all amino acids in a protein is called a gene.
Triplet code is genetic code made of three nucleotides, which
codes for one amino acid in a protein.
Properties of
Genetic code
Triplet
Universal Degenerate Not overlap
Each sequence of
The same triplet
Meaning that some
Meaning that, no
as codon.
acid in all living
Which means that
part of the
genetic code, codes amino acids have more base of a given
or RNA is referred to for the same amino than one genetic code. triplet enter to be
three base on DNA
With four different
organisms.
bases, there are 64 Which is strong
possible codons,
evidence that all
which is more than
living organisms
enough to specify the originate from the
20 different amino same group.
acids that occur in
proteins.
Note that, the fact that the genetic
code is universal means that
genetic engineering is possible
(eg. inserting the human gene,
coding for insulin into bacteria for
mass production as bacteria is
able to make the same protein,
insulin)
there are more codons adjacent triplet.
than the number of
amino acids.
Where arranging four
bases in triplets gives
64 possible
combinations, so 61
possible codons for
20 amino acids (and
3 stop codons), so
more than one codon
specifies an amino
acid, this minimizes the
effect of mutation.
Proved using
point mutation/
substitution (a
change in a single
base of the DNA
code).
Transcription
1. Part of the DNA (gene) unwinds and unzips
due to the break of hydrogen bonds.
2. The anti-sense strand acts as a template, where free
activated RNA nucleotides line up against the template
strand according to the complimentary base pairing rule
(where A pairs with U and C pairs with G).
3. The free nucleotides join together by RNA
polymerase forming mRNA molecule.
4. The process ends when the chain reaches the stop codon
(ATT, ATC, ACT) and mRNA separates from the DNA
template strand allowing the DNA chains of the double helix
to rejoin.
5. Then mRNA leaves the nucleus through the nuclear
pores in the nuclear membrane to the ribosome in the
cytoplasm.
Translation
Translation takes place in the ribosome and it involves the conversion of the
code on mRNA into a protein in the ribosome in the cytoplasm.
The triplet code on mRNA is called a codon, where each codon codes for a
particular amino acid.
The mRNA attaches to ribosome.
Ribosome is made from a rRNA (ribosomal RNA) and a protein, with small
and large subunit.
TRNA
1. tRNA has anticodon which is complimentary to a particular codon on mRNA.
2. The other end of tRNA is a site where a specific amino acid can attach under
a control of specific enzyme, using energy from ATP forming tRNA-amino acid
complex.
3. The tRNA molecule carries its amino acid to the ribosome where its specific
anticodon links up with corresponding mRNA codon.
4. A peptide bond is formed between amino acids by condensation reaction.
Note that, there are 20 different amino acids, so there must be at least
20 different codons and 20 different anticodons, in fact there are
more than this since genetic code is degenerate meaning that one amino
acid can be coded for my more than one codon.
Start codon initiates translation which is AUG on mRNA that codes for the
amino acid methionine (methionine is later removed from the chain if not
needed in the structure)
The final three bases in the gene are stop codons which are either UAA,
UGA or UAG on mRNA, these don’t code for an amino acid and are
known as stop codons.
Stop codons cause ribosome to detach and therefore, terminate
translation.
The synthesis of the particular polypeptide chain coded for by that
particular gene is complete.
Note that, the fact that the genetic code is universal means that genetic
engineering is possible (eg. inserting the human gene, coding for insulin into
bacteria for mass production as bacteria is able to make the same protein,
insulin)
Steps of translation
1. The mRNA attaches to the small subunit of ribosome, where six
bases are exposed to the large subunit.
2. The tRNA with complimentary anticodon UAC (carrying
methionine amino acid) binds with hydrogen bonds to the mRNA at
the start codon AUG.
Note that, start codon initiates translation which is AUG on mRNA that
codes for the amino acid methionine (which can be later removed from
the sequence of not needed in the structure).
3. Another tRNA brings along a second amino acid, the anticodon of
the second tRNA binds to the codon on mRNA.
(two tRNA molecules fit into the ribosome at any one time, bringing
two amino acids side by side)
4. The two amino acids are held closely together and peptide bond is
formed between methionine and the second amino acid.
5. This is a condensation reaction catalyzed by peptidyl transferase
which is found in the ribosome.
6. The first tRNA molecule is then released and the ribosome moves
along the mRNA to bring the next codon in position of translation and the
third tRNA molecule binds.
7. More tRNA molecules arrive at mRNA and add their amino acids to
the growing chain of polypeptide until stop codon is exposed to ribosome
which stops further translation (i.e. terminates translation) and does not
code for amino acids.
8. Polypeptide is released and enters the endoplasmic reticulum and the
ribosomal subunits float independently in the cytoplasm.
Note that, a single mRNA can be translated by several ribosomes at the
same time. Thus, several identical polypeptide chains are synthesized
from one mRNA.
Comparison between mRNA and tRNA
Similarities
1. Both are made up of RNA nucleotides.
2. Both have a ribose sugar.
3. Both have uracil base.
4. Both single stranded.
Differences
1. mRNA is straight while tRNA is folded.
2. mRNA has no hydrogen bonds while tRNA has
hydrogen bonds holding its structure together.
3. mRNA has codon while tRNA has anticodon.
4. mRNA does not carry amino acids (no amino acid
binding site) while tRNA carries amino acid (has an amino
acid bindings site).
5. mRNA is found in the nucleus and cytoplasm while
tRNA is found only in the cytoplasm.
6. the length of mRNA is determined by the size of gene
while the length of tRNA is fixed.
Usually, several ribosomes work on the
same mRNA strand at the same time.
They are visible, using an electron
microscope, as polyribosomes (mass
production)
1. So a single mRNA can be translated
by several by ribosomes at the same
time.
2. thus several identical polypeptide
chains are synthesised from one
mRNA.
ab
r
Summary
lg
First :Role of mRNA:
Produced by transcription.
Important in translation by using base sequence to make polypeptide chain.
Where it leaves nucleus moving towards ribosome
It attaches to the small subunit of ribosome.
Carry codons where each codon codes for a particular amino acid.
tRNA binds and bring specific amino acids to the ribosome.
where its specific anticodon links up with corresponding mRNA codon.
8.
9.
10.
11.
According to the complementary base pairing( A=U, CΞG)
Example of codon on mRNA AUC and its complementary anticodon will be UAG.
single mRNA can be translated by several by ribosomes at the same time (polyribosomes).
mRNA is short lived where it can produce proteins for short period of time.
Dr
.N
iha
1.
2.
3.
4.
5.
6.
7.
Second :Role of tRNA:
1. At the one end of tRNA there is a site where a specific amino acid can attach under the
control of specific enzyme.
2. tRNA carries amino acids to ribosome.
3. where its specific anticodon links up with corresponding mRNA codon.
Dr.NIhal Gabr
146
4.
5.
6.
7.
8.
According to base pairing ( A=U, CΞG).
Two tRNA binds to the ribosome at the same time.
two amino acids are held closely together.
For peptide bond formation.
tRNA can be reused by binding to another amino acid.
Third :Role of ribosome:
.N
iha
lg
ab
r
1. Its important for translation.
2. Where The mRNA attaches to
the small subunit of ribosome,
six bases at a time are exposed
to the large subunit.
3. mRNA has codes for specific
sequence of amino acids in a
polypeptide chain.
4. Ribosome moves along the
mRNA one codon at a time.
5. Ribosome provides sites for
attachment of the two tRNA at a time.
6. Where each tRNA carries specific amino acid, so 2 amino acids are held close together.
7. With its specific anticodon links up with corresponding mRNA codon.
8. Peptide bond formed between 2 amino acids, through a condensation reaction catalysed by
peptidyl transferase which is found in ribosome.
9. Assembly of amino acids into primary structure.
Dr
Fourth :comparisons:
mRNA
tRNA
Straight
Folded
No hydrogen bonds
Hydrogen bonds holding the structure together
Codons
Anticodons
No amino acids binding site
Has amino acid binding site
Found in nucleus and cytoplas
Found in cytoplasm
Length depend on size of gene
Size/ Length is fixed
Dr.NIhal Gabr
147
Polypeptide
Monomers are nucleotides
Monomers are amino acids
There are only four different nucleotides
There are 20 different amino acids
Nucleotides are linked together by phosphodiester
bonds
Amnio acids are linked together by peptide bonds.
Made of 2 strands
Only one
One structure( alpha- helix)
Takes primary , secondary , tertiary or quaternary
structure)
DNA replication
DNA Transcription
All the DNA molecule is replicated/ copied.
Only the gene(length of the DNA ) is transcribed/
copied
Both strands act as templates
Only One strand is involved
Complementary base pairing A-T
Where thymine is used as complementary base to
adenine.
Complementary base pairing A-U
Where uracil is used as complementary base to
adenine.
Controlled by DNA polymerase enzyme
Controlled by RNA polymerase enzyme.
Free activated RNA nucleotides are joined
Which has ribose.
lg
Free activated DNA nucleotides are joined
Which has deoxyribose
ab
r
DNA
mRNA produced which is single stranded and
straight.
.N
iha
Two DNA molecules produced
Where each is double stranded and helical
Molecules produced are double stranded DNA
Molecule produced is single stranded mRNA
Important in mitosis, meiosis
Important in protein synthesis
1.
2.
3.
4.
5.
6.
7.
8.
Dr
Fifth :protein synthesis and release from cell
Gene in DNA transcribed forming mRNA using DNA as template in nucleus.
mRNA contains code for polypeptide.
mRNA leaves nucleus to cytoplasm where it binds/associateswith ribosome.
tRNA molecules attached to specific amino acids.
tRNA with specific amino acid carried to ribosome.
pairing of codons on mRNA with anticodon on tRNA.
Formation of peptide bond between adjacent amino acid .
Protein formed enters the rough endoplasmic reticulum .
9. The proteins are then modified ( ex; glycosylation)
10. Then protein can be released from plasma cell where vesicles move to cell surface membrane
via cytoskeleton, vesicle then fuse with cell surface membrane (exocytosis) using energy from
ATP.
Dr.NIhal Gabr
148
Important questions
Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
Semiconservative replication allows the formation of new DNA molecules
that are genetically identical to each other and to their mother. Thus,
lowering the risk of mutation (i.e. change in base sequence), so that the
proteins produced will always be functional.
Points missing
ab
r
•results in genetically identical daughter cells.
All bacteria grown will have the heavy
N15 N15
&
isotope, N15 in their DNA.
Ni
ha
lG
•having same structure/function and genetic sequence as parent cell.
ag
wa
n
Bacteria grown will have both isotopes of
N15 N14 N15 N14
N15 N14 N14 N14 N15 N14 N14 N14
Dr
.N
nitrogen therefore will be hybrid.
Dr.Nagwan Gabr& Dr. Nihal Gabr
280
Gene mutation
Alteration in DNA by sudden random change of base sequence of DNA.
Causes of mutation
•error during DNA replication, as errors are copied during replication
when wrong bases are inserted.
•exposure to a mutagen which may be either a chemical, such as mustard
gas or tobacco smoke or physical such as X-rays and UV rays.
Types of mutation
Chromosomal mutation
Gene mutation
Point mutation
Frame shift
(Substitution)
Deletion
A change in a single base of the DNA
Where one nucleotide is
code (i.e. affects one triplet code)
Can have one of three effects
Silent mutation
Non sense
Missense
Insertion
Where one nucleotide is
missed out, so the entire
inserted twice, so the
mutation is changed. So
after mutation is changed
for after mutation are
different.
(one base removed, thus
shifting the reading frame
base sequence is altered. entire base sequence is
Where each triplet after altered. Where each triplet
The altered codon the whole gene is
and code of an entirely
can be silent mutation corresponds to a stop corresponds to
different and code for an different protein, as all
codon (i.e. stop signal) different amino
where the altered
entirely different protein, amino acids coded for
codon corresponds to so new polypeptide
acid.
as all amino acids coded after mutation are now
The base substitution The altered codon
the same amino acid. chain might be shorter.
(i.e degenerate new
codon which
corresponds to same
amino acid)
now different.
(one base added, thus
shifting the reading
forward one place).
frame backward one
place).
Note that, the closer the mutation to the start
Chromosomal mutation
Chromosomal mutation
Change in position of entire
genes within chromosome.
of the base sequence, the greater the effect.
Whole chromosome mutations
The loss or duplication of whole chromosome during meiosis.
Example, Down syndrome, which is caused by a whole
chromosome mutation at chromosome 21.
6 Errors in DNA replication can give rise to mutations.
The diagram shows the bases in a length of DNA.
Length of DNA
A
T
G
C
T
C
A
T
T
T
A
C
C
A
T
C
G
A
Base number
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18
The table shows the genetic code for the amino acids.
Genetic
code
AAA
AAG
AAC
AAT
Amino
acid
Lysine
Genetic
code
CAA
CAG
Asparagine
CAT
CAC
Threonine
CCA
CCC
CCG
CCT
Arginine
CGA
CGC
CGG
CGT
AGC
AGT
Serine
CTA
CTC
CTG
CTT
ATA
ATC
ATT
Isoleucine
ATG
Methionine
ACA
ACC
ACG
ACT
AGA
AGG
Amino
acid
Glutamine
Genetic
code
GAA
GAG
Amino acid
Genetic
code
Amino acid
Glutamic acid
TAC
TAT
Tyrosine
Serine
Histidine
GAC
GAT
Aspartic acid
TCA
TCC
TCG
TCT
Proline
GCA
GCC
GCG
GCT
Alanine
TGG
Tryptophan
Arginine
GGA
GGC
GGG
GGT
Glycine
TGC
TGT
Cysteine
Leucine
GTA
GTC
GTG
GTT
Valine
TTA
TTG
Leucine
TTC
TTT
Phenylalanine
The genetic codes TAA, TAG and TGA are stop codons.
(a) State the sequence of the first four amino acids coded for by this length of DNA.
Methionine, Leucine, Isoleucine, Tyrosine
(1)
. . . . . . . . . . . . .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
14
*P62792RA01428*
(b) A change in a single base can cause a change in the amino acid sequence
produced in protein synthesis.
(i) Name the type of each mutation described below.
(2)
Substitution
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (missense)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................ . . . . . . . . . . . . . . . . . . . . .
Base number 3 becomes cytosine (C) ...............
Deletion
Base number 6 becomes number 5 in the sequence...................................................................................................................
.....................
Insertion
Base number 9 becomes number 10 in the sequence ................................................................................................................
....................
*(ii) Explain the possible effects of these three types of mutation on the amino
acid sequence coded for by this length of DNA.
Use the information in the table to support your answer.
(6)
Substitution (point mutation)
. . . . . . . . . . . . .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
Where there is a change in a single base of one triplet code (i.e. codon).
. . . . . . . . . . . . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ ............................................................................................................................... . . . . . . . . . . . . . . . . . . . . . .
This may result in one of the three possibilities,
mutation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
. Silent
. . . . . . . . . . . ...................................
Where the altered codon will code for the same amino acid due to the fact that the triplet codes (i.e.
. . . . . . . . . . . . .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
genetic codes) are degenerate.
Example, if base 6 was replaced with adenine then the new codon (CTA) still codes for Leucine.
. . . . . . . . . . . . .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... . . . . . . . . . . . . . . . . . . . . . .
Nonsense
. . . . . . . . . . . . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
Where the altered codon will be a stop codon.
. . . . . . . . . . . . .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
Example, if base 12 was replaced with Adenine.
Missense
. . . . . . . . . . . . .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... . . . . . . . . . . . . . . . . . . . . . .
Where the altered codon corresponds (i.e. codes for) another amino acid.
. . . . . . . . . . . . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... . . . . . . . . . . . . . . . . . . . . . .
Example, if base 3 was replaced by cytosine, this will code for Isoleucine instead of methionine.
. . . . . . . . . . . . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
Deletion
Where one base is removed, causing the entity sequence to be altered (shifting the reading frame
. . . . . . . . . . . . .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... . . . . . . . . . . . . . . . . . . . . . .
backward one place), so all amino acids after mutation will be altered.
. . . . . . . . . . . . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... . . . . . . . . . . . . . . . . . . . . . .
Example, removal of base 4 causes the to become methionine, serine, phenylalanine, threonine.
. . . . . . . . . . . . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
Insertion
. . . . . . . . . . . . .................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... . . . . . . . . . . . . . . . . . . . . . .
Where one base is added twice, causing the entire sequence to be altered (shift the reading
frame forward one place), so all amino acids after mutation will be altered.
. . . . . . . . . . . . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
Example, adding T between base 9 and 10, so sequence becomes leucine, proline, serine.
. . . . . . . . . . . . ................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ ............................................................................................................................... .. . . . . . . . . . . . . . . . . . . . .
(Total for Question 6 = 9 marks)
*P62792RA01528*
15
Turn over
Gene mutation
Change in nucleotide (i.e. base sequence) of DNA, so a new allele is formed. This can
happen by substitution, deletion or insertion.
This change leads to change in the transcribed mRNA (i.e. mRNA with altered
codons).
In case of substitution, a new amino acid with different R groups may be incorporated
into the growing chain of polypeptide at the ribosome during translation.
Causing change in primary structure of protein (i.e. amino acid sequence on
polypeptide) which in turn causes change in three dimensional shape of protein, so
different protein with altered function or totally un functional protein may be produced.
Note that, mutation can lead to cancer, characterized by uncontrolled cells division to
form a mass of functionless cells known as tumor.
Why most mutation have no observable effect?
•occur in non coding DNA.
•code is degenerate.
•one allele might be altered.
•DNA repair mechanism.
How change in DNA base sequence might lead to loss of enzyme activity?
Mutation takes place where there is a change in base sequence of gene, so a new allele is
formed. Resulting in changed mRNA codons (i.e. base sequence of transcribed mRNA is
changed). So different tRNA with different anticodon will be involved, as tRNA will carry
different (incorrect) amino acid to the ribosome. So incorrect amino acid is incorporated into
the the growing polypeptide chain, so change in amino acid sequence (i.e. primary structure of
protein is changed). So polypeptide will fold differently, leading to change in tertiary structure
(3D shape). So the active site will have a different shape/charge. So substrate no longer
binds to active site.
Genetic disorders are disorders resulting from defect in gene such as sickle cell anemia which
results from point mutation (i.e. substitution) where different base is incorporated in the DNA
base sequence resulting in the formation of a new allele (i.e form of gene).
Allele formed is recessive, therefore the person affected carries homozygous recessive allele (i.e.
carries two copies of the defective allele).
Pattern of inheritance
Gene
A length of DNA coding for specific protein, thus determining specific characteristics
(i.e. traits).
Alleles
Are alternative forms of same game.
Dominant
Allele is expressed in phenotype whether the individual is homozygous or heterozygous
for that allele.
Recessive
Allele is expressed in phenotype only when individual is homozygous for that recessive
trait (i.e. both alleles coding for recessive trait).
Homozygous (homozygote)
An individual when both alleles coding for a particular characteristic are identical.
Heterozygous (heterozygote)
An individual where the two alleles coding for particular characteristic are different.
Genotype
Genetic makeup of an organism with respect to a particular feature or combination of/
pair of/two/all alleles present in an organism of particular trait.
Phenotype
All characteristics of an organism which is determined by the interaction between
genes (genotype) and environment (observable features).
True breeding
A homozygous organism that always produce the same offspring when crossed with
another true breeding organism for the same characteristic.
(which means parents must be both dominant or both recessive).
Mono hybrid cross
A genetic cross where only one gene for one characteristic is considered.
Test cross
A test made to find out the genotype of an individual with dominant phenotype for a
particular gene by crossing it with one to have the homozygous recessive genotype for
the same gene.
To reveal the parental genotype (i.e. being homozygous dominant or heterozygous).
Codominance
When pair of alleles are equally dominant, so in heterozygous where both alleles at a
gene are fully expressed in the phenotype. Example include blood groups.
•Cystic fibrosis is a serious genetic disorder that is causers by faulty allele on autosome,
which affects the production of mucus by epithelial cells.
•CFTR gene is a large gene, meaning that it is at higher risk of mutation, where mutation in
this gene leads to abnormal CFTR (cystic fibrosis trans membrane regulator) protein and
cause sticky mucus.
Effect of cystic fibrosis on air ways
•If the person carries the normal CFTR gene, then CFTR protein is synthesized and can
function properly, where CFTR channel protein allows the movement of chloride ions out of
the epithelial cells -through CFTR channel proteins- and into the mucus. Sodium channels are
inhibited by CFTR so sodium ions remain outside cells in the mucus. Therefore, mucus
becomes hypertonic thus, water moves out of epithelial cells into the mucus by osmosis,
resulting in thinner watery mucus. So cilia can beat, moving mucus away from airways (i.e.
bronchi and bronchioles).
•Mutation in the CFTR gene (i.e. faulty/defective allele) leads to change in primary structure
of protein, which in turn causes a change in the tertiary structure of the protein. So CFTR
cannot function properly therefore, chloride ions build up inside cells as well as sodium
channels are not inhibited so sodium ions move into epithelial cells so the cytoplasm becomes
hypertonic. Water therefore, leaves the mucus and enters cells by osmosis, so the mucus
becomes thick and sticky. So cilia cannot beat, so it cannot move mucus away -as it is too
thick- which will accumulate in the airways (i.e. bronchi and bronchioles) reducing rate of gas
exchange. Also, mucus traps dust and bacteria -bacteria has ideal growth conditions in the
mucus- so can cause infections. So the person starts coughing to remove mucus which will
damage the cells lining airways.
Treatments of cystic fibrosis
•antibiotics to prevent and treat chest infections
•medicines to make the mucus thinner and easier to cough up
(mucolytics)
•medicines to widen airways and reduce inflammation.
•physiotherapy to dislodge mucus for efficient gas exchange.
Symptoms of cystic fibrosis
The respiratory system
The digestive system
•Where thick, sticky mucus builds up in the •Thick sticky mucus causes
airways (i.e. bronchi and bronchioles) so
blockage of the pancreatic duct,
narrowing airways. Thus, reducing air flow so no enzymes (i.e. amylase,
into the alveoli -less ventilation- which in
lipase and trypsin) reaching the
turn reduces the concentration gradient
duodenum, so no digestion of
The reproductive system
In women
Egg produced, yet female has a
weak chance of fertility due to,
•Thick mucus which can block the
cervix and so sperm cannot reach
In sweat glands
Normally, CFTR allows chloride
ions to move into epithelial cells, so
less chloride ions in sweat as well as
reducing water loss and preventing
dehydration.
carbohydrates, fats and proteins, the egg.
CFTR mutation causes less chloride
reducing gas exchange (i.e. less diffusion of so they cannot be absorbed.
•Thick mucus blocks the oviduct so ions to move into endothelial cells, so
oxygen into the blood and carbon dioxide •Also, excessive build up of
decreasing chance of fertilization. more salts (i.e. chloride and sodium)
into the alveoli), so reduced supply of
mucus on villi cause reduced
•Implantation impaired.
are lost in sweat, so water moves by
oxygen to respiring cells, so less aerobic
surface area available for
In men
osmosis out of epithelial cells
respiration, so less ATP thus resulting in
absorption. So less absorption of •Lack of vas deference which is the
increasing chance of dehydration.
tiredness and lack of energy.
nutrients, which leads to
tube carrying sperm out of the
•Besides, coughing due to the sticky mucus malnutrition.
testes into semen.
which cannot be moved away by cilia.
•Moreover, enzymes trapped in •Vas deference is present, yet it
•Moreover, mucus fill up the lungs
the pancreas will start digesting may be partially of totally blocked
containing trapped particles of dust and
cells of the pancreas, thus
by thick mucus so, less or no sperm
bacteria (pathogens), where mucus provides affecting cells producing insulin
leaving testes.
optimum conditions for bacterial growth so so person might get diabetic.
between the blood and the alveoli, so
bacteria replicates increasing susceptibility
to lung infection where antibacterial affect
will stop due to thick mucus.
Fifth: 2C.5 :Genetic screening:
When whole population ( large number of people) are tested for genetic disease.
To be able to identify carriers.
Its important to diagnose the genetic diseases as early as possible to improve the chances of survival
and their general state of health.
Process:
• If one member of a family is born with genetic disease such as cystic fibrosis......so other
•
ab
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lg
•
•
.N
iha
•
members of the family will be offered genetic testing.
Diploid somatic cells are used and analysed ( gametes are not used as it has half the DNA
and the mutation might be missed).
All possible CFTR mutations are tested as its a large gene .
If one partner in a couple knows he is a carrier, so the other partner is advised to be
tested as well.
Because if two carriers have a baby there is a 1 in 4 risk that it will be affected by genetic
disease( cystic fibrosis).
Value of this
Dr
More cost efficient , as though screening costs money , it is much cheaper than caring for
severely affected children for rest of parent’s lives.
Carriers to faulty allele, have the option to take a decision regarding having a child:
1. Take the 1 in 4 risk of getting a diseased child, and have a family hoping the children inherit
normal healthy alleles.
2.
decide not to have a child at all.
3.
To get pregnant and undergo prenatal screening then take a decision .
Dr.NIhal Gabr
165
Genetic testing
B. Preimplantation
genetic diagnosis
A. Prenatal screening
Chorionic villus
sampling
Amniocentesis
A. Prenatal screening
ab
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A. Amniocentesis
Dr
.N
iha
lg
• To find if unborn child has a disease:
1. Removing 20 cm3 of amniotic fluid
using needle and a syringe.
2. Done at week 16 of pregnancy
3. Amnion sample taken has fetal
epithelial cells and blood cells .
Fetal DNA is Cultured for 2-3 weeks
then screened.
Disadvantages
1. Done after 16 weeks (late in
pregnancy) , results takes 2-3
weeks , so difficult on parents to
terminate pregnancy if
necessary( traumatic).
2. It carries0.5%-1% risk of
spontaneous abortion after the
procedure, regardless of genetic
status.
3. Not offered for all pregnant
women as test is expensive.
Dr.NIhal Gabr
166
Advantages
1. Less
miscarriage risk
B. Chorionic villus sampling:
• To find if unborn child has a disease:
1. Sample taken from developing
placenta between 8 and 12 weeks of
pregnancy.
2. Then DNA analysed for recessive
faulty allele
Advantages
Disadvantages
1. Carried earlier in
pregnancy, so if
termination is
necessary , it is
physically less
traumatic for
mother.
2. Results are
available faster.
3. Larger sample
taken allowing
wide testing
range of genetic
diseases.
.N
iha
lg
ab
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1. Sex-linked characteristic
( alleles on X chromosome)
can’t be detected by this
technique as all parental X
chromosomes are inactivated
in fetal placental cells.
2. There is 0.5-1%risk that
embryo may spontaneously
abort after the tissue sample
taken , though still the risk of
miscarriage at this stage of
pregnancy is high anyway .
B. Preimplantation
genetic diagnosis
A parent already have a family history or child affected by genetic disease
So they can carry preimplantation genetic diagnosis based on the technique of IVF.
In this technique, the egg and sperm are fertilised outside the body.
After few cell divisions, a single cell is removed from each embryo.
Genetic make up is checked and only those embryos free of the problem alleles are
placed in the mother’s uterus to implant snd grow.
• This removes the faulty allele from the gene pool.
• In case of genetic diseases found only in boys such as (haemophilia) , only female
embryos would be implanted.
Dr
•
•
•
•
•
Disadvantages
1. IVF requires the female to take high doses of hormones
which may be carcinogenic.
2. Not all people can afford to pay for IVF.
Dr.NIhal Gabr
167
ab
r
lg
A. Ethical
.N
iha
Problems with genetic testing:
Dr
1. Risk of false positive or negative result
(inaccurate).
2. Healthy fetus may be aborted if false
positive result,
3. May result in miscarriage/ spontaneous
abortion of fetus.
4. Ethical concerns as its a potential
life(killing unethical).
5. Who has the right to decide if test should
be done and terminating life of fetus/fetus
has the right to life.
B. Social
1. Social stigma of having disabled
child.
2. Cost implications to health service
or individuals
3. Social pressure.
4. Religion issues
Problems with genetic testing:
1. This is when trained experts known as genetic counselors provide help
- By awarness of the disease and how to prepare / manage it.
- Helps indecision marking according to ethical ,social and religious issues.
Dr.NIhal Gabr
168
Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
For women with cystic fibrosis, egg is produced but they find it difficult to
be fertile since thick, sticky mucus traps the cervix so the sperm cannot
reach the egg. Also, thick mucus blocks the oviduct so decreasing chance
3
January 2015
Ni
ha
lG
ab
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of fertilization and implantation impaired due to mucus.
Code: WBI01/01
2C.2. Patterns of inheritance
.N
ag
wa
n
&
(4)
Paper 1
Individual person 8 is
homozygous recessive.
Therefore, 5 and 6 are both
Dr
heterozygous.
The PKU disorder is a recessive genetic disorder meaning that in order for
individuals to express the phenotype, both alleles must be effected (i.e. homozygous
recessive). Therefore, if the offspring is affected this means that both parents have
the allele for PKU disorder, yet they are both unaffected so they have heterozygous
genotype.
Dr.Nagwan Gabr& Dr. Nihal Gabr
298
Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
2C.2. Patterns of inheritance
(3)
The fact that both parents are heterozygous means that they both carry one
recessive allele in their genotype, therefore gametes produced contain either the
dominant or recessive allele. By using a punnet square, the probability of the child
Dr
.N
ag
wa
n
&
Ni
ha
lG
ab
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being homozygous recessive is calculated, which would be 25%.
Dr.Nagwan Gabr& Dr. Nihal Gabr
300
Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
Three samples of same mass are taken from the tubers (potatoes) of both DHARmodified plants and GDP-modified plants. Crush the samples and add distilled water to
extract vitamin C. Using same volume of extract, titrate using same concentration of
DCPIP, by adding DCPIP drop by drop to the extract solution until the blue color of the
ab
r
DCPIP remains. Measure the volume of DCPIP used for the solution to remain blue (i.e.
lG
reach end point where all vitamin C has been oxidized). (Standardization) Repeat the
titration procedure using 1% vitamin C solution and measure the volume of DCPIP used
Ni
ha
for solution to remain blue, compare the volume of DCPIP used with that of the extract
solutions from potato tubers. Then compare the vitamin C concentration in tubers
Dr
.N
ag
wa
n
&
taken from both modified plants. Repeat and take avenge results.
2C.2 Patterns of inheritance
Dr.Nagwan Gabr& Dr. Nihal Gabr
309
Points missing
•Grow both types of
plants under same
conditions
•titrate DCPIP against
extract.
Biology
8
Topic 2: Membranes, proteins, DNA and Gene Expression
May 2017
Code: WBI01/01
2C.2. Patterns of inheritance
Paper 1
Allele that is expressed only when the genotype is homozygous for that allele (i.e. allele
that is only expressed in the absence of dominant allele).
Points missing
lG
ab
r
•allele is an alternative form (i.e. version) of the same gene.
Ni
ha
Genetic pedigree diagram shows the alleles in the parental gametes and the probability of
them crossing together to give possible offspring genotypes that can result from the
combination of alleles during fertilization. The hemochromatosis is caused by recessive
Marking scheme points
&
homozygous genotype, where both alleles must be affected to show the phenotype.
ag
wa
n
•shows the family history where parents and genotypes for each generation are identified.
•phenotypes are identified (allows identification of individuals with or without condition.
•for HC/recessive condition, two normal/unaffected parents any have one or more
Dr
.N
offsprings that are affected.
Dr.Nagwan Gabr& Dr. Nihal Gabr
313
Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
9
January 2018
Code: WBI01/01
Paper 1
2C.4. Cystic fibrosis (linked to 2A.6. The mammalian gas exchange system)
(2)
CFTR is a chloride ion channel protein
Cystic fibrosis is caused by a faulty (i.e. defective) allele, so the primary structure of synthesized
protein is different so different folding and coiling of polypeptide chain, which in turn changes the
tertiary structure of protein. So the CFTR protein cannot function properly and so will not allow
ab
r
movement of chloride ions out of cells. Also, sodium channels are not inhibited so sodium ions
move into epithelial cells so cells become hypertonic to mucus so water leaves the mucus into cells
lG
by osmosis. So mucus becomes thick and sticky so cilia cannot beat and therefore, cannot move
mucus away from airways (i.e. bronchi and bronchioles), thus reducing air flow to the alveoli, so
Ni
ha
reducing ventilation which in turn reduces the concentration gradient between the alveoli and the
blood which leads to reduced gas exchange, where less oxygen moves into blood from the alveoli
Dr
.N
ag
wa
n
&
and less carbon dioxide moves into the alveoli.
2C.5. Genetic screening
(2)
Dr.Nagwan Gabr& Dr. Nihal Gabr
315
Biology
10
Topic 2: Membranes, proteins, DNA and Gene Expression
May 2018
Code: WBI01/01
2C.1. Gene mutation
Paper 1
lG
2C.4. Cystic fibrosis
ab
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Alteration in DNA by sudden random change the the base sequence of DNA.
Ni
ha
(6)
Cystic fibrosis is a recessive genetic disorder which is caused by faulty (i.e.
&
defective) allele carried on autosome. Where a person requires two forms of the
same gene (i.e. two faulty alleles) to show the phenotype (in absence of dominant
ag
wa
n
allele). So the parents might be carriers for the disease, meaning that they have
heterozygous genotype. Where both parental gametes had recessive allele so the
child had homozygous recessive allele and so showed phenotype of cystic fibrosis.
Points missing
.N
•cystic fibrosis causes abnormal non functional CFTR protein
Dr
•also, mutation may have occurred in formation of gametes (i.e. post fertilization)
Dr.Nagwan Gabr& Dr. Nihal Gabr
317
Topic 2: Membranes, proteins, DNA and Gene Expression
ab
r
Biology
lG
As age increases from 5 to 25 years, the percentage of people with cystic
fibrosis infected with P.aeruginosa bacterium increases by 48%, the percentage
Ni
ha
then remains constant in 35 years group at 82% then decreases by 7% in 45
years group.
Where as age increases from 5 to 15 years, the percentage of people with cystic
&
fibrosis infected with S.aureus bacterium increases by 3%, it then showed
ag
wa
n
continuous decrease as it decreased by 20% in the 45 years group from 15
years old group.
.N
Cystic fibrosis affects the production of mucus where mucus becomes thick and
Dr
sticky so cilia lining airways cannot beat, and so cannot move mucus away from
bronchi and bronchioles. Where mucus traps dust and bacteria as well as it
provides optimum conditions for bacterial growth so bacteria replicates
increasing the susceptibility to lung infection.
Person starts coughing to remove mucus which will damage cells lining airways.
Dr.Nagwan Gabr& Dr. Nihal Gabr
318
DO NOT WRITE IN THIS AREA
(b) (i) Suggest how the function of the CFTR protein will be affected by a class IV mutation.
(2)
Class IV mutation affects the movement of chloride ions out of cells.
. . . . . . . . . . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. .. .. .. .. .. .. .. .. .. ..
Where CFTR is a chloride ion channel protein where mutation in CFTR
. . . . . . . . . . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. .. .. .. .. .. .. .. .. .. ..
causes accumulation of chloride ions in epithelial cells as chloride ions
. . . . . . . . . . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. .. .. .. .. .. .. .. .. .. ..
cannot pass through channel protein into mucus.
. . . . . . . . . . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. .. .. .. .. .. .. .. .. .. ..
. . . . . . . . . . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. .. .. .. .. .. .. .. .. .. ..
. . . . . . . . . . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. .. .. .. .. .. .. .. .. .. ..
(ii) Suggest how the CFTR protein is broken down in a class VI mutation.
(2)
CFTR is a protein where protease enzyme can hydrolyze and break
the protein into amino acids.
. . . . . . . . . . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. .. .. .. .. .. .. .. .. .. ..
By breaking down peptide bonds.
. . . . . . . . . . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. .. .. .. .. .. .. .. .. .. ..
. . . . . . . . . . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................................................................................................................ .............. .. .. .. .. .. .. .. .. .. .. ..
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DO NOT WRITE IN THIS AREA
DO NOT WRITE IN THIS AREA
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*P54656A01724*
17
Turn over
Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
Point mutation (i.e. substitution) involves the change in one base of DNA sequence, which may
have one of three effect. The base substitution may be silent mutation where the defective
codon, codes for the same amino acid (i.e. degenerate codon coding for same amino acid). The
base substitution may be non sense where the defective codon codes for stop codon (i.e. stop
signal) so the new poly peptide formed will be shorter. The base substitution may be missense
ab
r
where the defective codon codes for different amino acid.
2C.2. Patterns of inheritance
(8)
Deletion involves one
nucleotide in the DNA
Ni
ha
lG
sequence being missed out so
A person can be shown to have the disorder, either by showing the
Points missing
ag
wa
n
screening to show their genotype.
&
phenotype which is reduced levels of urea in their urine or by genetic
•blood test/biochemical test
.N
•pedigree analysis/family history
the reading frame is shifted
backwards one place, the
entire base sequence after
mutation is changed where all
triplets after the mutation are
affected so the entire gene is
altered coding for different
protein, where all amino acids
coded for after mutation are
different. Insertion involves
one nucleotide in the DNA
Dr
sequence being inserted
twice thus, shifting the
reading frame forward one
place.
The closer the deletion or
insertion to the start of the
sequence the greater the effect
as more triplet codes are
changed.
Dr.Nagwan Gabr& Dr. Nihal Gabr
331
Biology
Topic 2: Membranes, proteins, DNA and Gene Expression
Cystic fibrosis is a serious genetic disorder caused by gene mutation which results in
the production of faulty (i.e. defective) allele that causes the synthesis of protein with
different primary structure, so the tertiary structure of protein is different, resulting in
non functional protein. Where CFTR channel protein does not does not allow the
movement of chloride ions outside epithelial cells so they accumulate inside cells. Also,
sodium channels are not inhibited so sodium moves into epithelial cells, thus lowering
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the water potential inside cells where cytoplasm becomes hypertonic to the mucus. So
water moves out of the mucus into the cells. So the mucus becomes thick and sticky so
lG
cilia cannot beat and so cannot move mucus away from airways so mucus
accumulates in airways, containing trapped particles of dust and bacteria. Where
Ni
ha
mucus provides optimum conditions for bacterial growth so bacteria replicates causing
infection where muscles become inflamed.
2C.5. Genetic screening
Dr
.N
ag
wa
n
&
(8)
Parents who are carriers carry out preimplantation genetic diagnosis where only healthy fetus are
implanted into uterus or decide not to have children.
Dr.Nagwan Gabr& Dr. Nihal Gabr
335
8a)
ii) Cystic fibrosis causes reduced diameter of the lumen, thicker or inflamed muscle as well as
more mucus.
Where cystic fibrosis results in the production of thigh and sticky mucus due to mutation in the
CFTR gene (so faulty CFTR allele). The CFTR protein is not functioning properly, affecting
the transfer of chloride ions so water moves out of mucus.
Diameter of lumen is reduced due to the build up of mucus, where cilia cannot beat so cannot
move mucus away as it is too thick.
Mucus is sticky so traps bacteria, where bacteria has ideal growth conditions in mucus so
bacteria replicates causing infections. Infection damages cells lining airways leading to
inflammation of muscles.
Topic 2: Membranes, proteins, DNA and Gene Expression
Unethical to kill potential life.
Healthy fetus may be aborted.
Ni
ha
Risk of false positive or negative diagnosis.
lG
ab
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Biology
Risk of miscarriage or spontaneous abortion.
Dr
.N
ag
wa
n
&
No one has the right to decide whether the fetus should live or not.
Dr.Nagwan Gabr& Dr. Nihal Gabr
336