A Level Biology - Enzymes MCQs (15)

The diagram shows a metabolic pathway. What would be the effect of adding a small amount of a non-competitive inhibitor of enzyme 2?

• A - enyzme 2 would be partially denatured

• B - substance X would increase in concentration

• C - substance Y would no longer be formed

• D - the initial reactant would no longer be metabolised

The painkiller ibuprofen reduces the activity of an enzyme involved in the production of prostaglandin. Ibuprofen binds reversibly to the active site of the enzyme.

Which type of enzyme inhibition describes this example and why?

• A - competitive inhibition because ibuprofen alters the shape of the enzyme

• B - competitive inhibition because ibuprofen and the substrate cannot bind at the same time

• C - non-competitive inhibition because ibuprofen blocks the active site

• D - non-competitive inhibition because ibuprofen has the same shape as the substrate

Which letter in the flow diagram shows the effect of adding a competitive inhibitor to an enzyme-catalysed reaction:?

• A

• B

• C

• D

A fixed volume of the enzyme catalase was added to a fixed volume of hydrogen peroxide solution.

The diagram shows how the concentration of product changed over the course of the reaction.

What explains the shape of this graph?

• A The active sites become saturated.

• A The active sites become saturated.

• C

  The hydrogen peroxide inhibited the reaction.

• D The substrate molecules were used up.

A fixed volume and concentration of substrate and enzyme were mixed. All other variables were kept constant.

The enzyme-catalysed reaction was left until it was complete.

Which graph shows how the rate of reaction changes with time?

• A

• B

• C

• D

What could be used to calculate the rate of an enzyme-catalysed reaction?

1 the appearance of product

2 the disappearance of substrate

3 the Michaelis-Menten constant (Km)

• 1 and 2

• 1 and 3

• 1 only

• 2 and 3

The effect of substrate concentration on an enzyme-catalysed reaction was measured in three different conditions. The graph shows the results.

Which statement is correct?

• A - X is a competitive inhibitor which binds to a site other

  than the active site of the enzyme.

• B - X is a non-competitive inhibitor which has a similar shape to the active site of the enzyme.

• C - Y is a competitive inhibitor which has a similar shape to the active site of the enzyme.

• D - Y is a non-competitive inhibitor which binds to a site other than the active site of the enzyme.

Four students investigated the effect of catalase on hydrogen peroxide.

Each student started a digital clock at the beginning of the experiment and stopped the clock after 25 bubbles had been counted. The time recorded on the digital clock is shown in the table.

Which of the times recorded by the students is appropriate for this experiment?

• 1.34 minutes

• 1 minute 33.54 seconds

• 94 seconds

• 93.54 seconds

An investigation was carried out on the effect of temperature on an enzyme-catalysed reaction. The enzyme and its substrate were initially placed into separate test-tubes and raised to the temperature required. They were then mixed and placed into four tubes A, B, C and D. These tubes were incubated for the time and at the temperature stated. The mass of the product formed was then measured.

In which tube was the rate of reaction highest?

• A

• B

• C

• D

The graph shows energy changes in a chemical reaction. What is the activation energy when an enzyme is added?

• A - 1+2

• B - 2 only

• C - 3-2

• D - 4