Biological molecules
Learning objective:
•To consolidate learning of
biological molecules
Which molecule, A to E,
(a) is one of the
monomers which
combine to form
starch;
• D
(b) contains peptide
bonds;
• A
(c) could be an oil;
• B
What is the
remaining
molecule?
•An amino acid
(d) is one of the
molecules that form a
triglyceride?
• E
Carbohydrates
• Grasses store carbohydrate as fructans, which are polymers
of a monosaccharide called fructose.
• The diagram shows the structural formula of each of two
fructose molecules.
• (a) (i) Draw a box round the parts of the two fructose
molecules that would be removed when the two molecules
are joined together. (1 mark)
• (ii) Name the process in which monosaccharides join
together.
• Condensation
• (iii) How many carbon atoms does a molecule of
fructose contain?
• 6
(b) The table shows the percentage of carbohydrates in
the dry mass of a sample of young grass.
• (i) The sample of young grass contains 80% water.
Calculate the mass of cellulose in 1 kg of this grass.
Show your working.
– 25% of 20% of total mass= 5%
– 5% of 1kg = 50g
– 50 gains 2 marks.
– 25% × 200, or equivalent, gains 1 mark.
• (ii) Cellulose is a constituent of the cell walls of the grass.
• Explain how the structure of cellulose molecules gives
strength to the cell walls
• Long straight chain (of glucose molecules) / 1-4 link in
context;
• Hydrogen bonds hold molecules together;
• able to form (micro)fibrils.
• (c) Cows feed on grass, but they do not produce enzymes
that can digest cellulose or some of the fructans. The
rumen is large and contains microorganisms which
secrete enzymes that can break down cellulose and
fructans. Use information from the table in part (b) to
explain the advantage to cows of having such
microorganisms in their rumen.
• High proportion/'lots'of carbohydrate unused if
cellulose/fructans
• not digested / 'lots' of energy wasted.
• (not just: 'grass has a lot of cellulose & fructans')
Lipids
In humans, triglycerides are stored under the skin in
the cells of the adipose layer.
Triglycerides are compounds of glycerol and fatty
acids.
(a) Explain why the adipose layer is described as a
‘tissue’.
•
Cells all the same/similar structure/function.
(b) The structural formula of glycerol is:
The structural formula of a fatty acid is:
R – COOH.
(i) In the space below, draw the structural formula of a
triglyceride.
(ii) Name the process in which fatty acids are combined with
glycerol.
• Condensation / esterification.
(c) (i) Describe the effect on melting point of including
unsaturated fatty acids in a triglyceride.
Unsaturated fatty acids/ lower the melting point.
(ii) Analysis of the triglycerides in adipose tissue shows that
about 50% of the fatty acids are unsaturated. Suggest the
advantage of this.
• Triglycerides are oils / melting point below body
temperature;
• Explanation of advantage,
– e.g. prevents hard layer of fat forming under skin /
mobility of lipid / deposition in arteries.
(d) Triglycerides are broken down in the digestive system.
(i) Name the enzyme that digests triglycerides.
• Lipase.
(ii) Name one organ which produces this enzyme.
• Pancreas/salivary glands/small intestine