Enzymes Quiz

9. 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?

• The active sites become saturated.

• 2. The enzyme was denatured.

• 2. The hydrogen peroxide inhibited the reaction.

• 2. 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

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

• 2 and 3

• 2 only

15. An experiment was carried out in which the enzyme lipase was used to hydrolyse a triglyceride.

    The pH was recorded at regular intervals during the reaction. The results are shown in the table. At 14 minutes unreacted triglyceride was still present. What explains the results after 10 minutes?

• 1. The end-products acted as competitive inhibitors

• 1. The end-products acted as non-competitive inhibitors.

• 1. The enzyme reaction had reached Vmax.

• 1. The tertiary structure of the enzyme had been lost.

15. Which statement about the effect of substrate concentration on the activity of an enzyme is correct?

• 1. Above a certain concentration of substrate an enzyme reaches its maximum rate of reaction.

• 1. At high concentration of competitive inhibitor increasing the substrate concentration has no

     effect.

• 1. At high substrate concentration a non-competitive inhibitor no longer affects the enzyme activity.

• 1. The higher the concentration of substrate the faster an enzyme can catalyse a reaction.

13. The graph shows the results of an investigation into the effect of amylase on starch at three different temperatures.

14. Which statements are correct conclusions using these results?

15. 1) The optimum temperature is 50 °C.

16. 2) The initial rate of reaction is highest at 70 °C.

17. 3) The higher the temperature the more quickly the enzyme denatures.

• 1, 2 and 3

• 1 and 2 only

• 1 and 3 only

• 2 and 3 only

Substances called furanocoumarins are found in some fruits, where they act as inhibitors of the enzyme CYP3A4. This enzyme is needed to break down toxins in the human digestive system, so dangerous levels of these toxins may develop if these fruits are eaten.

What does this information suggest about molecules of the enzyme CYP3A4?

• 1. They lower the activation energy of the toxin breakdown process.

• 1. They show specificity for a particular substrate found in fruits.

• 1. They will change permanently when acted upon by furanocoumarin molecules.

• 1. They will resume normal activity when levels of furanocoumarins decrease.

In two investigations, the rate of an enzyme-catalysed reaction was measured in the presence of

either a competitive inhibitor or a non-competitive inhibitor.
What could be the effect of increasing the substrate concentration on each rate of reaction?

• A

• B

• C

• D

Two enzymes, X and Y, were used in an experiment.

Enzyme X was from bacteria that live in rivers and lakes at temperatures from 5 °C to 20 °C. Enzyme Y was from bacteria that live in hot water springs at temperatures from 40 °C to 85 °C.

The experiment measured the concentration of product produced by each enzyme at temperatures between 0 °C and 100 °C after 5 minutes.

Which graph shows the results?

• A

• B

• C

• D

Two enzymes are added to a solution containing a low concentration of a substrate that they can both use.

Which statement is correct?

• 1. Both enzymes will use equal amounts of the substrate.

• 1. Neither enzyme will be able to use the substrate.

• 1. The enzyme with the lower Vmax will use less of the substrate than the other enzyme.

• 1. The enzyme with the lower Vmax will use more of the substrate than the other enzyme.