Exam-Style Questions: Biological Molecules and Enzymes

1. a) The diagram shows the formula of a molecule of an organic compound.

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(i) To which group of organic compounds does this molecule belong?

(1 mark)

(ii) Give one way in which this molecule differs from other compounds in the group.

(1 mark)

b) The table shows some of the organic compounds found in a bacterial cell.

Compound Percentage of total dry mass Number of different types of molecule
Protein 55 1050
RNA 20.5 463
DNA 3.1 1
Lipid 9.1 4
Glycogen 2.5 1

(i) Glycogen and protein are both polymers. Explain why there can only be one type of glycogen molecule, but there can be many types of protein.

(2 mark)

(ii) Explain why there are many types of RNA found in this cell.

(2 mark)

(Marks available: 6)

Answer

Answer outline and marking scheme for question: 1

Give yourself marks for mentioning any of the points below:

a) (i) Amino acid.

(ii) Possession of CH3 group/different R group.

(2 marks)

b) (i) Glycogen consists of glucose/one type of monomer.

Many different amino acids combine to form proteins.

(ii) Include messenger and transfer RNA.

Each gene gives/each protein will be derived from a different messenger RNA.

Each amino acid has a different transfer RNA.

(Max 4 marks)

(Marks available: 6 marks)

2. Succinate is converted to fumarate by the enzyme dehydrogenase. This reaction can be inhibited by adding malonate.

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a) Use this information to explain how malonate acts as an inhibitor.

(2 marks)

b) In an investigation succcinate dehydrogenase is mixed with a solution containing both succinate and malonate.

What will happen to the rate of fumerate production when the concentration of succinate is increased?

(2 marks)

(Marks available: 4)

Answer

Answer outline and marking scheme for question: 2

Give yourself marks for mentioning any of the points below:

a) Similar (chemical) structure and shape.

Competes for active site.

(2 marks)

b) Increased rate of fumarate production.

Less competition at active site.

(2 marks)

(Marks available: 4 marks)

3. (a) Give two functions of proteins in cell surface membranes.

(2 marks)

b) The composition of the inner and outer membranes of a mitochondrion is shown in the table.

Phospholipid % Protein %
Outer Membrane 45 55
Inner Membrane 25 75

Suggest an explanation for the difference in the percentage of protein present in the two mitochondrial membranes.

(2 marks)

(Marks available: 4)

Answer

Answer outline and marking scheme for question: 3

Give yourself marks for mentioning any of the points below:

a) Carrier molecule; enzyme.

Receptor site for hormones/antibodies.

Transport gate/channel protein.

Antibody.

(max 2 marks)

b) More protein, more enzyme/channel protein.

Used in oxidative phosphorylation/production of ATP/electron transport chain.

(2 marks)

(Marks available: 4)