Chemistry of life & nucleic acids and proteins (Topics SL2, HL6)
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What are the three most common
elements found in living organisms?
_________________________
_________________________
_________________________
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Write down the general formula for
carbohydrates: _______________
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A __________, or long chain molecule,
is made up of many __________, or
single subunits.
The table below shows some of the other elements required by living organisms.
Complete it to show one function for each of the elements in plant & animal cells:
Element
Role in plants
Role in animals
Nitrogen (N)
Calcium (Ca)
Phosphorus (P)
Iron (Fe)
Sodium (Na)
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What is the difference between:
a) An atom and an ion?
________________________________________________________________
________________________________________________________________
________________________________________________________________
b) Covalent and ionic bonding?
________________________________________________________________
________________________________________________________________
________________________________________________________________
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What is the definition of an organic substance?
________________________________________________________________
________________________________________________________________
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Water (H2O) is essential for all living
systems. Water molecules are
described as ________ because they
have an uneven charge distribution
within the molecule as a whole. The
oxygen atom is slightly __________
charged, and the two hydrogen atoms
have a slight __________ charge.
This means that __________ bonds
can form between adjacent water
molecules, giving water many of its
unique properties.
Page 1 of 6
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Sketch a diagram to show the structure
and polarity of water:
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Complete the table to show how the properties of water make it significant in living
systems:
Characteristic
Transparency
Explanation
Example(s) of significance
in living systems
Light passes through water.
Movement of water up through
the xylem tissue of plants.
Cohesion
Surface tension
Thermal properties
Water has a high
specific heat capacity
Large amounts of energy are
required to heat up water and
change its state. Conversely,
much energy also has to be lost
by water in order to cool it.
Solvent properties
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Draw the basic structure of a generalised amino acid in the space below. Label the
different groups:
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What is the most simple possibility for the ‘R’ group within the amino acid? __
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Two amino acids (peptides) are joined together during a __________ reaction to form
a __________, and one molecule of ________. The link between the two amino
acids is called a __________ bond. Condensation reactions between many amino
acids produce a __________ (or protein) molecule.
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Complete the diagram over the page to show a condensation reaction. The opposite
of this reaction is called __________ - in other words, breaking down the protein
molecule.
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H
R
N
H
C
O
C
H
H
R
+
OH
N
O
C
H
→
C
H
OH
+ H2O
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Primary structure of a protein is simply the sequence of the amino acids within a
polypeptide chain, in other words, the order in which the amino acids are bonded
together.
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Secondary protein structure has three possibilities. Sketch and label diagrams of
the following types of secondary structure found in proteins:
1) α-helix
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2) β-pleated sheet – parallel
Amino acids form ions in solution when the hydrogen ion from the carboxyl group
dissociates, and forms an NH3+ ion with the amino group:
H
R
N
H
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3) β-pleated sheet - antiparallel
C
H
O
H
→
C
O
H
H
+
H
R
N
C
O
C
H
O –
Hydrogen bonds, ionic bonds, and disulphide bridges may form between different
sections of the polypeptide chain (shown below as a coiled spring), thus maintaining
tertiary structure.
Hydrogen bond
Ionic bond
disulphide bridge
fig3.26
fig 3.24
fig 3.25
p96
p95
p95
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Protein molecules are made up of
many amino acids with peptide bonds
between them. There are four levels
of protein structure:
Lysozyme:
(Showing
tertiary structure)
fig 3.35
p104
1) Primary structure is simply the
sequence (order) of the _______
________ within the polypeptide chain.
disulphide
bridge
2) Secondary structure may be either
an α-helix or a β-pleated sheet. The βpleated sheet may be __________ or
__________ in form. In each case
__________ bonds maintain the
structure.
3) Tertiary structure is the way in which
the entire polypeptide chain is twisted
and folded into a specific, fixed shape.
The chain is held in shape by
di__________ bridges, _________
bonds, _________ bonds and
__________ bonds.
4) Quaternary structure is found where
several polypeptides interact to form a
protein molecule, for example,
haemoglobin – four polypeptides.
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Haemoglobin:
(Showing
quaternary structure)
Label the types of structure found in
the diagram of the enzyme lysozyme:
fig 3.36
Protein types:
Type
Nature
Function
Fibrous
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Secondary structure most important.
Insoluble in water.
Physically tough.
Long parallel polypeptide chains
cross-linked (by hydrogen bonds) at
intervals forming long fibres or
sheets.
Structural. eg collagen.
(tendons, bones), myosin
(in muscle), silk (spider’s
webs), keratin (hair,
horn, nails, feathers).
Globular
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Tertiary structure most important.
Polypeptide chains are tightly folded
to form a spherical shape.
Easily soluble.
Form enzymes, antibodies
and some hormones, eg
insulin.
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Page 4 of 6
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Functions of proteins. Complete the table:
Name of protein
Type
Amylase
enzyme
Keratin
structural
Function
respiratory pigment
Fibrinogen
protective
hormone
helps to regulate glucose
level in blood.
contractile
moving filaments in muscle
tissue.
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Draw a diagram of the ring structure of α-D-glucose in the space below:
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Glucose is an example of a monosaccharide. Two monosaccharides may be joined
together during a ______________ reaction to form a _____________. A molecule
of water is released during this process. The bond formed between the two
monosaccharide molecules is a __________ bond. When condensation reactions
occur between many monosaccharides a ______________ molecule is formed, for
example, starch. The opposite of condensation is __________ - breaking down the
molecule. Complete the table below:
Type of carbohydrate
Example
Monosaccharide
1)
2)
Disaccharide
1)
2)
Polysaccharide
1)
2)
Page 5 of 6
Function
Not required
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A lipid molecule is made up
of one molecule of
___________ covalently
bonded to three ________
________ molecules. The
fatty acid molecules are
bonded to the glycerol
molecule during
condensation reactions.
During the formation of one
lipid molecule, three
__________ molecules are
produced. A lipid molecule
may be broken down during
a __________ reaction.
= hydrocarbon chain
K
E
Y
H
O
C
H
C
OH
HO
O
C
H
C
OH
HO
O
C
H
C
OH
HO
H
Glycerol
+
Three fatty
acids
condensation
reaction
= H and O atoms that form
water during the
condensation reaction.
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Complete the diagram to
show the products of the
condensation reaction:
Complete the table:
Type of lipid
Function
Phospholipid
Insulation under the skin of animals, buoyancy in
aquatic mammals, energy storage.
Cholesterol
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Most small carbohydrate molecules are __________ because they have –OH (
__________) groups which are able to form __________ __________ with water
molecules.
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Most lipids are __________ because they have a long, __________ (uncharged)
hydrocarbon chain.
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Proteins with –OH ( __________ ) groups or other charged areas are __________.
Non-polar proteins are insoluble.
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In general, solubility of any substance decreases, as molecular size increases.
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