Proteins T2

Question 1

Muscle cells contain globular and fibrous proteins.
Compare and contrast the molecular structures of globular and fibrous proteins.
(4)

Answer 1

-Both are chains of amino acids joined by peptide bonds.
-Both contain hydrogen bonds, disulphide bridges, ionic bonds.
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-Globular proteins have hydrophilic groups on the outside, whereas fibrous proteins have hydrophobic groups on the outside.
-Globular have tertiary or quaternary structures, whereas fibrous have little or no tertiary structure.
-Globular are folded into compact shapes whereas fibrous have long chains.

Question 2

State why enzymes are described as biological catalysts.

1

Answer 2

Reduce activation energy of biological reactions.

Question 3

Describe an experiment that could be carried out to investigate the effect of enzyme
concentration on the initial rate of reaction.
(4)

Answer 3

• Using a range of enzymes concentrations (5+).
• Substrate concentration not limiting.
• Mixing.
• Measure rate soon after mixing, plot and calculate rate from linear part of graph.
• Control variable- Temp, ph, volume of substrate.
• Repeats at each enzyme concentration.
• Control, tube used with no enzyme/distilled water.

Question 4

Lysozyme is an enzyme found in tears. Lysozyme can destroy some bacteria by
breaking down the polysaccharide chains that form part of their cell walls.
The primary structure of lysozyme is a specific sequence of 129 amino acids.
Two of the amino acids that make up the active site are in positions 35 and 52 in
the primary structure.
Suggest how these two amino acids could be brought closer together to form
part of the active site of this enzyme.
(3)

Answer 4

• Formation of secondary/tertiary structure.
• Bonding between R groups.
• Ionic bond, disulphide bridges.

Question 5

Lysozyme is an enzyme found in tears. Lysozyme can destroy some bacteria by
breaking down the polysaccharide chains that form part of their cell walls.
Temperature affects the activity of lysozyme.
Suggest why increasing the temperature above 45 °C causes a decrease in the
activity of lysozyme.
(2)

Answer 5

• Increasing temperature changes the bonding in the enzymes.
• The active site denatures/changes shape.
• The substrate no longer fits into the active site/ the enzyme no longer catalyses the reaction/ no longer lowers the activation energy.

Question 6

Haemophilia is a disease that affects blood clotting. People with haemophilia are sometimes
given a protein called factor VIII. Factor VIII is an enzyme that is involved in the process of blood
clotting.
Explain how a change in the primary structure of factor VIII could cause difficulties with blood
clotting.
(4)

Answer 6

• Different primary structure results in a different sequence of amino acids.
• Change in R groups changes folding/bonding/secondary structure/tertiary structure.
• Changing shape/charge of active site, preventing substrate from being able to bind.
• Stopping/reducing the production of fibrin.

Question 7

Describe how a peptide bond is formed.

2

Answer 7

• Peptide bond formed by a condensation reaction.

- Between the (amine group/NH2) and the (carboxyl group/COOH) of adjacent amino acids.