Question 1

Which of the following best explains why enzymes are highly specific in their action?

Accepted Answer

Enzymes contain rigid active sites that only bind substrates with complementary shape and charge, as described by the lock-and-key model: $E + S \rightarrow ES \rightarrow E + P$.

Question 2

A patient is prescribed a drug that acts as a competitive inhibitor for an enzyme involved in cholesterol synthesis. Which of the following best describes how this drug works?

Accepted Answer

It competes with the substrate for binding at the active site, increasing $K_m$ but not affecting $V_{max}$.

Question 3

Which of the following vitamins is water-soluble and acts as a coenzyme in redox reactions?

Accepted Answer

Vitamin C

Question 4

Which statement about enzyme-catalyzed reactions is correct?

Accepted Answer

Enzymes lower the activation energy, $E_a$, but do not change the overall $9G$ of the reaction.

Question 5

Which of the following pairs of vitamins are both fat-soluble?

Accepted Answer

Vitamin A and Vitamin D

Question 6

A mutation causes an enzyme's active site to lose its charge complementarity with its substrate. What is the most likely effect?

Accepted Answer

The enzyme's catalytic efficiency will decrease due to reduced substrate binding.

Question 7

Which of the following best describes the role of a coenzyme in an enzyme-catalyzed reaction?

Accepted Answer

A coenzyme is a non-protein organic molecule that temporarily binds to the enzyme to assist in the transfer of chemical groups.

Question 8

Which of the following statements about the effect of temperature on enzyme activity is correct?

Accepted Answer

Enzyme activity increases with temperature up to an optimum, then decreases due to denaturation.

Question 9

Which of the following is an example of a zymogen?

Accepted Answer

Pepsinogen

Question 10

Which of the following statements about allosteric enzymes is correct?

Accepted Answer

Allosteric enzymes can be regulated by molecules binding at sites other than the active site, causing conformational changes.

Question 11

Which of the following best describes the effect of a noncompetitive inhibitor on enzyme kinetics?

Accepted Answer

It decreases $V_{max}$ without affecting $K_m$.

Question 12

Which of the following is NOT a function of vitamins in the human body?

Accepted Answer

Providing a direct source of energy

Question 13

Which of the following statements about the Michaelis-Menten constant ($K_m$) is correct?

Accepted Answer

$K_m$ is the substrate concentration at which the reaction rate is half of $V_{max}$.

Question 14

Which of the following is a correct pairing of vitamin and function?

Accepted Answer

Vitamin K: blood clotting

Question 15

Which of the following best describes the induced-fit model of enzyme action?

Accepted Answer

The enzyme's active site changes shape to better fit the substrate upon binding.

Question 16

Which of the following statements about cofactors is correct?

Accepted Answer

Cofactors can be either metal ions or organic molecules required for enzyme activity.

Question 17

A patient with a deficiency in vitamin B$_{12}$ is most likely to experience which of the following symptoms?

Accepted Answer

Impaired red blood cell formation (megaloblastic anemia)

Question 18

Which of the following best describes the role of a holoenzyme?

Accepted Answer

A holoenzyme is an active enzyme consisting of an apoenzyme plus its cofactor or coenzyme.

Question 19

Which of the following is an example of an enzyme that catalyzes the transfer of a phosphate group?

Accepted Answer

Hexokinase

Question 20

Which of the following statements about zymogens is correct?

Accepted Answer

Zymogens are inactive enzyme precursors that require chemical modification to become active.

Chapter 21

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