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Biological Molecules Exam Questions with Complete Answers
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Biological Molecules Exam Questionswith Complete Answers
(c) (i) Describe how you could use the biuret test to distinguish a solution of the enzyme,
lactase from a solution of lactose. - Answer-Lactase (enzyme) will give purple / lilac
colour;
OR
Lactose (reducing sugar) will not give purple / lilac and will remain blue.
(c) (ii) Explain the result you would expect with the enzyme. - Answer-Lactase (enzyme)
is a protein;
OR
Lactase contains peptide bonds.
Methotrexate is a drug used in the treatment of cancer. It is a competitive inhibitor and
affects the enzyme folate reductase.
(c) (i) Explain how the drug lowers the rate of reaction controlled by folate reductase. -
Answer-Methotrexate / drug is a similar shape / structure to substrate;
Binds to / fits / is complementary to active site;
Less substrate binds / less enzyme-substrate complexes formed
(c) (ii) Methotrexate only affects the rate of the reaction controlled by folate reductase.
Explain why this drug does not affect other enzymes. - Answer-Methotrexate / drug is
only similar shape to specific substrate / only fits this active site;
OR
Methotrexate / drug is a different shape to other substrates / will not fit other active sites;
2 (a) Induced fit and lock and key are two models used to explain the action of
enzymes.
(i) Describe the induced fit model of enzyme action. - Answer-Active site / enzyme not
complementary;
Active site changes (shape) / is flexible;
(Change in enzyme allows) substrate to fit / E-S complex to form;
(ii) Describe one way that the lock and key model is different from the induced fit model.
- Answer-Active site does not change (shape) / is fixed (shape) / is rigid / does not wrap
around substrate / (already) fits the substrate / is complementary (before binding);
,The diagram shows the structure of a molecule of PABA. It also shows the structure of a
molecule of a drug called sulfanilamide, which can be used to treat bacterial infections.
Sulfanilamide prevents bacteria producing folic acid.
(b) Use the diagram and your knowledge of enzymes to explain how sulfanilamide
prevents bacteria producing folic acid. - Answer-Similar structure / shape (to PABA) /
both complementary;
Competes for / binds to active site / competitive inhibitor;
Less PABA binds / less E-S complexes; OR Specific reference to different structure /
shape (to PABA);
Binds to position other than active site / binds to allosteric site / binds to inhibitor site /
non-competitive inhibitor;
Changes the active site so substrate cannot bind / less PABA binds / less E-S
complexes;
4 (a) Omega-3 fatty acids are unsaturated. What is an unsaturated fatty acid? - Answer-
Double bond(s); (Bonds) between carbon atoms.
Olestra is an artificial lipid. It is made by attaching fatty acids, by condensation, to a
sucrose molecule.
4 (c) (i) Name bond X. - Answer-Glycosidic;
(c) (ii) A triglyceride does not contain sucrose or bond X.
Give one other way in which the structure of a triglyceride is different to olestra. -
Answer-Contains glycerol / three fatty acids / forms three ester bonds;
1 (a) Some seeds contain lipids.
Describe how you could use the emulsion test to show that a seed contains lipids. -
Answer-1. Crush/grind;
2. With ethanol/ alcohol;
3. Then add water/then add to water;
4. Forms emulsion / goes white/cloudy;
(b) A triglyceride is one type of lipid. The diagram shows the structure of a triglyceride
molecule.
(i) A triglyceride molecule is formed by condensation. From how many molecules is this
triglyceride formed? - Answer-4/four
(ii) The structure of a phospholipid molecule is different from that of a triglyceride.
Describe how a phospholipid is different. - Answer-1. Phosphate/ PO4;
2. Instead of one of the fatty acids / and two fatty acids;
(iii) Use the diagram to explain what is meant by an unsaturated fatty acid. - Answer-1.
Double bonds (present);
2. Some/two carbons with only one hydrogen / (double bonds) between carbon atoms /
not saturated with hydrogen;
3. In (fatty acid) C/3;
, 7 Read the following passage.
Use information from the passage and your own knowledge to answer the following
questions.
7 (a) Name the monomers that make up the active site of the enzyme (lines 6 - 7). -
Answer-Amino acid / amino acids;
(b) (i) Aspirin only affects one of the enzymes in this pathway.
Use information in lines 5 - 7 to explain why aspirin does not affect the other enzymes. -
Answer-1. Affects one monomer/amino acid;
2. Not found in all active sites;
(c) Aspirin is an enzyme inhibitor. Explain how aspirin prevents substrate molecules
being converted to product molecules. - Answer-1. Occupies/blocks/binds to active site;
2. Substrate will not fit / does not bind / no longer complementary to / enzyme-substrate
complex not formed
Ponds provide a very stable environment for aquatic organisms.
Three properties of water that contribute to this stability are as follows:
• the density of water decreases as the temperature falls below 4 °C so ice floats on the
top of the pond
• it acts as a solvent for ions such as nitrates (NO3-)
• a large quantity of energy is required to raise the temperature of water by 1 °C.
Explain how these three properties help organisms survive in the pond. - Answer--- (ice
less dense because) molecules spread out;
P2 molecules form, crystal structure / lattice / AW;
P3 ice forms insulating layer /
ions / named ion, polar / charged;
-- P6 ions /named ion, attracted to / bind to / interact with, water;
S4 (named) organisms / plants / animals, uptake / AW, minerals / named mineral /
nutrients;
many / stable, (hydrogen) bonds between molecules;
-- Many hydrogen bonds between molecules
P8 at lot of energy to, force apart molecules / break bonds;
ACCEPT heat as alternative to energy
P9 high (specific) heat capacity;
DO NOT CREDIT latent heat capacity
S6 temperature does not change much / small variation in temperature; (gases still
soluble)
Explain the effect of increasing the concentration of substrate on the rate of reaction;
(i) without inhibitor, - Answer-1) more substrate, molecules enter active site:
2) more successful collisions between substrate and active site
3) ESCs, formed;
4) At low concentration not all active sites occupied / at high concentration all active
sites occupied;
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