Enzymes

Which of these statements describe the action of an extracellular enzyme?
1. Synthesis of a polynucleotide in the nucleus during DNA replication
2. Digestion of macromolecules in the lumen of the small intestine
3. Synthesis of ATP molecules in the mitochondria

• 1 and 2

• 1 and 3

• 3 only

• 2 only

The graph shows energy changes in a chemical reaction.

What is the activation energy when an enzyme is added?

• 1 + 2

• 2 only

• 3 - 2

• 4 only

The graph shows the effect of an enzyme on a reaction.

Which labels are correct?

• X is the reaction without the enzyme, W is the activation energy.

• X is the reaction with the enzyme, Z is the overall energy change.

• Y is the reaction with the enzyme, W is the difference in activation energy.

• Z is the energy gained by the product, W is the activation energy with the enzyme.

The following statements are about enzymes.
1. Folding of an enzyme molecule causes the formation of the active site.
2. The shape of the active site changes to enable the substrate to bind.
3. Temporary bonds hold the substrate in the active site.

4. More enzyme-substrate complexes are formed at the optimum temperature.

Which statements are correct for the induced fit hypothesis?

• 1 and 2

• 1 and 3

• 2, 3 and 4

• 2 and 4 only

The diagram shows an enzyme, its substrate and an enzyme/substrate complex.

Which statement explains how the substrate is able to enter the active site of the enzyme?

• Contact between the substrate and the enzyme causes a change in the enzyme shape.

• The shape of the active site and the shape of the substrate are complementary.

• The substrate within the active site forms hydrogen bonds with amino acids.

• When the enzyme/substrate complex forms, the tertiary structure of the enzyme changes.

An enzyme was added to a small excess of its substrate. All variables were kept constant.
A student was asked to sketch a graph to show how the concentration of the enzyme-substrate complex changes over time.
Which graph shows this correctly?

• A

• B

• C

• D

A student carried out experiments to investigate the effect of enzyme concentration on the rate of hydrolysis (break down) of protein in milk.
When the enzyme and milk were mixed, the protein was hydrolysed and the mixture changed from cloudy to clear.
The student investigated five different enzyme concentrations and recorded the time taken to reach the end-point for each.
What is an appropriate control for this investigation?

• Carrying out a further experiment where the enzyme solution is replaced with water.

• Carrying out each experiment in a thermostatically regulated water-bath at 35 °C.

• Performing three repeat experiments for each of the five enzyme concentrations.

• Using the same volume of enzyme solution for each of the five experiments.

The graph shows the results of investigations into the effect of amylase on the hydrolysis of starch at three different temperatures.

In each investigation the concentration and volume of the solutions was kept constant.

Which conclusion may be drawn?

• 50 °C is the optimum temperature of amylase.

• At 60 °C all the starch is hydrolysed after 30 minutes.

• At 70 °C the amylase is denatured before hydrolysis is complete.

• The rate of hydrolysis of starch is faster at 50 °C than at 70 °C.

Which features are correct for a competitive inhibitor of an enzyme-catalysed reaction?

• A

• B

• C

• D

Which statements about non-competitive enzyme inhibitors are correct?
1. The inhibitor can bind to the enzyme whether or not the enzyme has its substrate bound in the active site.
2. The inhibitor may bind at an allosteric site.
3. The inhibitor may not prevent substrate binding at the active site, but will prevent product formation.

• 1, 2 and 3

• 1 and 2 only

• 1 and 3 only

• 1 and 3 only