Monomers - A relatively simple molecule which is used as a basic
building block for the synthesis of a polymer.
e.g : monosaccharides, amino acids, nucleotides
Polymers - A giant molecule made from many similar repeating subunits
(monomers) joined together in a chain.
e.g: polysaccharides, proteins, nucleic acids
Macromolecules - A large molecule such as a polysaccharide, protein
or nucleic acid.
They are formed by condensation reactions between smaller molecules. All
polymers are macromolecules.
Lipids are not macromolecules - bsc their monomers are not
covalently bonded.
Carbohydrates
● C, H, O
● Hydrogen: Oxygen - 2:1
Cn(H2O)n
● 3 main groups - Monosaccharides, disaccharides, polysaccharides.
●
Carbohydrates make up about 1/10 of the organic matter in a cell, their
functions include:
○ Energy Sourceage - They provide the enegry for respiration.
Good source due to the large number of C- H bonds that can be
broken to release energy.
○ Energy Storage - They store energy
○ Structure - For example Cellulose
Monosaccharides
General formula-
(CH2O)n
●
Monosaccharides are the monomers of Carbohydrates.
●
3 types:
➔ Triosases (3C) - gylceraldehyde.
➔ Pentosases (5C) - Deoxyribose and Ribose - used to make RNA
➔ Hexosases (6C) - Glucose, fructose, galactose
● Pentoses and Hexosase are long enough to form more stable ring structures.
● In glucose, Carbon 1 joins to the Oxygen on Cazrbon 5. Crabon 6 is not part of
the ring.
●
When Glucose forms a ring structure, it can do so in two different ways. If the
OH at C1 is below the plane of the ring, it is called an α Glucose,
●
if the OH at C1 is above the plane of the ring, it is called β Glucose. This
difference in structure leads to a difference in properties.
●
Monosaccharides can be bonded together (for example, to produce a
disaccharide, or maybe even a polysaccharide, like Starch) with a Condensation
Reaction, forming a Glycosidic Bond. It is a covalent bond.
●
This bond can be broken by Hydrolysis. The bond is named after the Carbon
atoms that are involved in the bond, for example, the bond between two
Glucose molecules in Amylose is called a (1→4) Glycosidic Bond, as the bond is
between C1 of one monomer and C4 of another.
Disaccharides
A sugar molecule consisting of 2 monosaccharides joined together by a glycosidic
bond.
● Maltose - Glucose + Glucose
● Sucrose - Glucose + Fructose
● Lactose - Glucose + Galactose
Polysaccharides
●
A polymer whose sub units are monosaccharides joined together by glycosidic
bonds.
● Storage polysaccharides- Starch (plants), Glycogen (animals). Its important to
store glucose in this form to avoid:
➔ Accumulation of glucose in the cells (osmotic imbalance)
➔ Glucose interfering with other reactions due to its high reactivity.
Starch
Mixture of amylose and amylopectin.
● Made up of glucose only.
●
Amylose
Many 1, 4 linked a-glucose molecules.
Amylose molecules tend to form coiled springs due to the way in which the the
glucose units bond, making it quite compact. They are Unbranched.
● Iodine molecules can become trapped within the 'coils' of the Amylose chain,
which causes iodine (in Potassium Iodide solution) to change colour
from yellow-brown to blue-black.
●
Amylopectin.
1, 4 Linked a- glucose(shorter chains) with branched 1, 6 linkages.
●
The branches are formed when a one end of a chain joins with a glucose in
another, forming a (1→6) Glycosidic Bond.
●
Starch grains are commonly found in chloroplasts and storage organs, e.g
potato tubers.
● The compact structure formed when the chains coil together, makes
it a good energy store. (takes up little space, Insoluble in water)
Glycogen
●
Made up of amylopectin like molecules.
● 1-4 linked a- glucose with 1-6 branches.
the chains of (1→4) linked glucoses are shorter, giving it a more highly
branched structure.
This branching allows for the fast breakdown of the molecule during
respiration as it means that there are more ends which enzymes can
start the proccess of hydrolysis from.
Glycogen molecules clump together to form granules.
●
Engergy storage molecules like Starch and Glycogen:
o are insoluble in water and so do not affect the water potential of cells.
o store glucose molecules in chains so that they can esily be 'broken off' and used
in respiration.
Cellulose - Strengthening material in plants
●
●
●
Cellulose is the most abundant polysaccharide found in nature.
Made up of β Glucose.
For a (1-4) glycosidic bond to be formed, one glucose molecule must be flipped upside
down. (Bcs the OH group on Carbon 1 is above the ring while that on Carbon 4 is below
the ring.)
●
The arrangement of B glucose molecules forms a strong structure of cellulose because
the H atoms of the -OH groups are weakly attracted to O atoms in the same cellulose
molecule or those of neighbouring molecules (Hydrogen bond)
●
A hydrogen bond = weak.
●
Cellulose molecules become cross-linked by hydrogen bonding to form chains.
●
Long Cellulose chains bunch together, to form Microfibrils. These Microfibrils are
bunched with other Microfibrils, held by more Hydrogen bonds, to
form Macrofibrils.
●
Macrofibrils have a very high mechanical strength, similar to that of steel. In plant
cell walls, they criss-cross over each, forming a cross-hatched structure, held by
Hydrogen bonds, which is very strong. This also allows water to move though and along
the cell wall. The strength of the cell walls prevent the cell form bursting, as it
would in an animal cell, when water passes into the cell. The pressure cause by the
water makes the cell Turgid, supporting the plant through Turgor Pressure.
●
Microfibrils can have special roles. For example, in Guard Cell Walls, the
arrangement of microfibrils allows the Stomata to open and close.
●
Cell walls have many layers of fibres (cross-ply structure) and other substances that:
Many H bonds = strong molecule
➔ help cross link the cellulose fibres
➔ Form a glue like matrix around the fibres which increases strength and
makes the material of the cell wall that is flexible.
●
Other Carbohydrate Polymers are used by a number of other organisms to provide
support, such as Peptidoglycan, which forms the basis of bacterial cell walls,
and Chitin, which makes up the exoskeleton of insects.
●
Because of the different structures of these Polysaccharides, they have very
different functions. Starch and Gkycogen are used as energy stores whereas
Cellulose plays a structural role.
Tests for carbs.
Starch
Reagent - Iodine or Potassium Iodide
Positive test - brown to blue-black.
Reducing sugars
Reducing sugars carry out reduction (they donate electrons) in this process they
become oxidised but are the reducing agent.
All monosaccharides are reducing sugars and some disaccharides. Sucrose is not.
● Reducing sugars are detected by the Benedicts test.
● Reagent - Benedict’s reagent (CopperII Sulphate)
● The reducing sugars reduce the soluble blue copper sulphate to
insoluble brick red copper oxide (copperI)
It is a Semi quantitative test - The degree of colour change can give an indication
of the conc of reducing sugars present.
Non Reducing sugars
Cannot donate electrons and cannot be oxidised
Lipids
● Lipids are made of the elements Carbon , Hydrogen and Oxygen, although
they have a much lower proportion of water than other molecules such as
Carbohydrates. They are insoluable in water.
● Lipids perform many functions, such as:
o Energy Storage -Have more C-H bonds than Carbs and so release more energy
o Making Biological Membranes
o Insulation
o Protection - e.g. protecting plant leaves from drying up
o Boyancy
o Acting as hormones
o Metabolic source of water - they also perform respiration to produce H2o and
CO2
● Most are made of Glyceride which has two molecules: Glycerol and Fatty
Acids.
● There are 3 main types of lipids:
➔ Triglyceride (1 glycerol, 3 Fatty acids)
➔ Phospholipids
➔ Steroids (e.g Cholesterol)
● A Glycerol molecule (alcohol) is made up from three Carbon atoms with
a Hydroxyl Group attached to it and Hydrogen atoms occupying the
remaining positions. (3 -OH groups)
Fatty Acids
● Fatty acids consist of an Acid Group at one end of the molecule(head) and a
Hydrocarbon Chain (tail) which is usually denoted by the letter 'R'.
● The tails with a Carbon double bond = Unsaturated lipids
These are good as it makes fatty acids melt more easily due to the kinks.
Most oils are unsaturated: 1 Carbon-Carbon double bond = monounsaturated.
More than 1 C-C double bond = polyunsaturated.
● Animals tend to have more saturated(bad), and consequently solid at room
temperature lipids whereas plants tend to have more unsaturated and so fluid at
room temperature lipids.
● Acid + Alcohol —------> Ester (Ester bond/linkage)
Triglycerides
● Triglycerides are lipids consisting of one glycerol molecule bonded with three
fatty acid molecules. The bonds between the molecules are covalent and are
called Ester bonds. They are formed during a condensation reaction.
● Triglycerides are hydrophobic and so insoluble in water. The charges are
evenly distributed around the molecule so hydrogen bonds do not form with
water molecules. (non polar)
Phospholipids
● Phospholipids are similar to triglycerides in they consist of a glycerol 'backbone'
and fatty acid 'tails', however, the third fatty acid has been replaced by a
phosphate group 'head'.
● While the fatty acid 'tails' are hydrophobic, the phosphate 'head' is hydrophilic.
This means the phosphate group will orientate itself towards water and away
from the rest of the molecule, and also gives rise to the special properties that
allow phospholipids to be used to form membranes.
● Phospholipids can contain saturated and unsaturated fatty acids. This allows for
the control of the fluidity of membranes, which is useful, for example, in
maintaining membrane fluidity at low temperatures.
Proteins
● Polymers made of amino acids.
● 2 types : Structural and Functional
Amino Acids
Many amino acids are held together by peptide bonds. (Polypeptide)
● Peptide bonds are created by enzyme catalysed condensation reactions and
broken down by enzyme catalysed hydrolysis reactions. Breaking down
proteins is important in many areas of the body, not merely in digestion. For
example, in hormone regulation, cells that are targeted by hormones contain
enzymes to break down those hormones. This stops their effects from being
permanent and allows them to be controlled.
Primary Structure
● The unique sequence of amino acids that make up a protein or polypeptide
chain is called the Primary Structure.
Primary Structure: The unique sequence of amino acids that makes up a
protein or polypeptide chain.
Secondary Structure
● After synthesis, polypeptide chains are folded or pleated into different shapes,
called their Secondary Structure.
● Two common examples of secondary structures are:
➔ Alpha Helices - a helical structure formed by a polypeptide chain
held in place by hydrogen bonds.
➔ Beta Pleated Sheets - a loose sheet like structure formed by
hydrogen bonding between parallel polypeptide chains.
Secondary structure is held together by many Hydrogen bonds, overall giving the
shape great stability.
Secondary Structure: The way in which the primary structure of a
polypeptide chain folds.
-
Occurs when the sequence of amino acids are linked by hydrogen
bonds.
Tertiary Structure
● The final 3D structure of a protein which occurs when there are attractions
between alpha helices or beta pleated sheets.
● Tertiary Structure: The final 3D structure of a protein, entailing the
shaping of a secondary structure.
-
The compact structure of a protein molecule resulting from the 3D
coiling of the amino acid chains.
● Tertiary structure is held together by four different bonds and interactions:
o Disulphide Bonds - Where two Cysteine amino acids are found together, a
strong covalent double bond (S=S) is formed between the Sulphur atoms
within the Cysteine monomers. (oxidation reaction)
o Ionic Bonds - If two oppositely charged 'R' groups (+ve and -ve) are found
close to each other, and ionic bond forms between them.
o Hydrogen Bonds - Your typical everyday Hydrogen bonds.
o Weak Hydrophobic Interactions - It occurs between R groups that are
non polar (hydrophobic). If the protein is in a watery environment, they tend
to come together, trying to avoid the water.
The hydrophobic parts are usually towards the proteins centre and
its hydrophilic parts are towards its edges.
● Tertiary structure can be broken by the action of heat. Increasing the kinetic
energy of protein with a tertiary structure makes it vibrate more, and so the
bonds that maintain its shape (which are mainly weak, non-covalent bonds) will
be more likely to break. When a protein loses its shape in this way it is said to
be Denatured. Even when cool the protein will not (or is highly unlikely to)
form its original complex shape.
● Proteins with a 3D structure fall into two main types:
o Globular - These tend to form ball-like structures where hydrophobic parts
are towards the centre and hydrophilic are towards the edges, which makes
them water soluble. (The water molecules cluster around their hydrophilic R
groups)
They usually have metabolic roles, for example: enzymes in all organisms,
plasma proteins and antibodies in mammals.
Their shape affects their function.
o Fibrous - They proteins form long fibres and mostly consist of repeated
sequences of amino acids which are insoluble in water. They usually have
structural roles, such as: Collagen in bone and cartilage, Keratin in
fingernails and hair.
Quaternary Structure
● Some proteins are made up of multiple polypeptide chains, sometimes with an
inorganic component (for example, a haem group in haemoglogin) called
a Prosthetic Group. These proteins will only be able to function if all subunits
are present.
Quaternary Structure: The structure formed when two or more
polypeptide chains join together, sometimes with an inorganic component,
to form a protein.
Its held together by the same bonds as those in the tertiary structure.
Haemoglobin
● Haemoglobin is a water soluble globular protein which is composed of 4
polypeptide chains. (Each chain is a protein called Globin)
● Alpha Globin makes up 2 of the chains while Beta Globin makes up the
other 2.
● The outward pointing hydrophilic R groups maintain its solubility.
In Sickle Cell anaemia - A polar amino acid on the Beta chain is replaced
with a different non-polar amino acid. The non-polar R group makes the
Hb less soluble, causing the symptoms of sickle cell.
● Each of the 4 polypeptide chains contains an Inorganic Prosthetic Haem
group. (a prosthetic group is an important + permanent part of a particular
protein molecule)
● Each Haem group contains an iron atom (One O2 molecule can bind with each)
Therefore a complete Hb molecule with 4 Haem groups can carry 4 O2
molecules.
● This group is responsible for the colour of Hb. If combined with O2 =
Oxyhaemoglobin (bright red). If not combined, the colour is darker.
Collagen
● Collagen is an insoluble fibrous protein consisting of three polypeptide chains
wound around each other.
● Each of the three chains is a coil itself (shape of a helix). Hydrogen bonds and
some covalent bonds form between these coils forming a 3 stranded rope. (triple
helix)
● Almost every 3rd amino acid is Glycine. Its small size allows the strands to lie
close together forming a tight coil.
● Each complete triple helix, forms a collagen molecule which interacts with other
collagen molecules running parallel to it by forming Covalent Cross Links
which are staggered along the molecules to further increase stability.
● Collagen molecules wrapped around each other form Collagen Fibrils which
themselves form Collagen Fibres.
● Collagen is flexible and has a high tensile strength. It is found in skin,
tendons, cartilage, bones, teeth, walls of blood vessels, etc.
● Collagen has many functions:
o Form the structure of bones
o Makes up cartilage and connective tissue
o Prevents blood that is being pumped at high pressure from bursting the walls
of arteries
o Is the main component of tendons, which connect skeletal muscles to bones
Hb vs Collagen
● Haemoglobin may be compared with Collagen as such:
o Basic Shape - Haemoglobin is globular while Collagen is fibrous
o Solubility - Haemoglobin is soluble in water while Collagen is insoluble
o Amino Acid Constituents - Haemoglobin contains a wide range of amino
acids while Collagen has 35% of it primary structure made up of Glycine
o Prosthetic Group - Haemoglobin contains a haem prosthetic group while
Collagen doesn't possess a prosthetic group
o Tertiary Structure - Much of the Haemoglobin molecule is wound into α
helices while much of the Collagen molecule is made up of left handed helix
structures
Water
Dipoles
Water is held by covalent bonds where the electrons are not shared completely
equally. Because oxygen is more electronegative than hydrogen, it has
a greater pull on the shared electrons.
●
➔ The O atoms get slightly more electrons —> slightly negative (δ-)
➔ The H atoms get slightly less electrons —> slightly positive (δ+)
This unequal distribution of charge is called a dipole.
● Dipoles occur in other molecules too, especially where there is an -OH, -CO or
-NH group.
● Molecules that have groups with dipoles are Polar.
● Polar molecules are Hydrophilic because the water molecules also
have dipoles and they attract each other.
● Molecules which don’t have dipoles are non-polar, they are not attracted to
water and so are Hydrophobic.
●
Hydrogen Bonds
The slightly negative and slightly positive regions of the water molecule are
attracted to charged regions of other molecules, forming Hydrogen
Bonds (which are weak in comparison with other chemical bonds). Water will
form Hydrogen Bonds within itself.
●
● It is a relatively weak bond formed by the attraction between a group
with a small positive charge on a H atom and another group
containing a small -ve charge.
The useful properties of water arise from its structure.
1. Water is a great solvent.
Water is good solvent for other polar molecules since it can interact with
the charged regions and dissolve the substance.
● It is also a good solvent for ionic substances, since the water
molecules cluster around the ions and separate them,
thus dissolving the substance. This property, along with the fact that water
is liquid over a wide range of temperatures, makes it ideal for acting as
a medium in which metabolic reactions can occur, and also as
a transport vehicle.
●
● Non-polar molecules are pushed together when surrounded by water, this
increases the stability of proteins and membranes.
2. High specific heat capacity.
Amount of heat energy required to raise the temperature of 1kg of water by 1℃.
● For the temp to be raised, molecules need to gain energy and move more.
●
Hydrogen bonds within water give it a high stability (makes it difficult to
separate the molecules or for them to move around.), which means that a large
amount of energy is required to raise the temperature of water. (the bonds
must be broken first to allow free movement.
● This allows water to store more energy for a given temperature rise and makes
water resistant to changes in temperature.
●
● This property means that oceans and lakes provide a stable
environment in which organisms can live. This also means that a large
amount of heat is required to evaporate water, so it is very useful
in cooling, for example, some animals sweat to cool down.
3. High Latent heat of vaporization.
Amount of heat energy required to vaporise a liquid. (changing it from liquid to
gas)
● Cohesion is the tendency of molecules within a substance to 'stick together'.
Water has a high Cohesion because of Hydrogen bonding. This gives water a
high latent heat of v because a lot of energy is needed for the hydrogen bonds to
be broken before the molecules can escape.
●
●
The energy taken up, results in a loss of heat from the surroundings, this makes
water a great Coolant in humans (sweating), plants during transpiration and
machines.