Question 1

Which of the following best describes the function of an enzyme in a biochemical reaction?

Accepted Answer

An enzyme lowers the activation energy, speeding up the reaction without affecting the equilibrium.

Question 2

A patient is exposed to mercury, which binds covalently to the –SH groups of cysteine residues in enzymes. What type of enzyme inhibition is this?

Accepted Answer

Irreversible inhibition

Question 3

Which equation correctly represents the general sequence of an enzyme-catalyzed reaction?

Accepted Answer

$$E + S \rightarrow ES \rightarrow EP \rightarrow E + P$$

Question 4

Which enzyme class catalyzes the transfer of a phosphate group from ATP to a substrate?

Accepted Answer

Transferase

Question 5

A reaction catalyzed by alcohol dehydrogenase is shown: $$\mathrm{CH_3CH_2OH} + \mathrm{NAD^+} \rightarrow \mathrm{CH_3CHO} + \mathrm{NADH} + \mathrm{H^+}. $$Which molecule is the substrate?

Accepted Answer

$$\mathrm{CH_3CH_2OH}$$

Question 6

Which factor does NOT directly affect the maximum rate of an enzyme-catalyzed reaction once the enzyme is saturated with substrate?

Accepted Answer

Substrate concentration

Question 7

Which of the following statements about enzyme specificity is correct?

Accepted Answer

Enzymes are usually specific for only one enantiomer of a chiral substrate.

Question 8

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

Accepted Answer

The enzyme changes shape to fit the substrate upon binding.

Question 9

A kinase catalyzes the following reaction: $$\mathrm{Fructose\ 6	ext{-}phosphate} + \mathrm{ATP} ightarrow \mathrm{Fructose\ 1,6	ext{-}bisphosphate} + \mathrm{ADP}. To $$which enzyme class does kinase belong?

Accepted Answer

Transferase

Question 10

Which of the following is a coenzyme required for oxidation-reduction reactions and is derived from niacin?

Accepted Answer

Nicotinamide adenine dinucleotide (NAD+)

Question 11

Which of the following statements about competitive inhibition is correct?

Accepted Answer

A competitive inhibitor binds to the active site, preventing substrate binding.

Question 12

Which vitamin acts as an antioxidant by donating hydrogen to oxygen-containing free radicals, and is then restored by vitamin C?

Accepted Answer

Vitamin E

Question 13

Which mineral is a cofactor for the enzyme alcohol dehydrogenase?

Accepted Answer

Zn$$^{2+}$$

Question 14

A patient has a deficiency in vitamin B12. Which coenzyme is most likely affected?

Accepted Answer

Coenzyme B12

Question 15

Which of the following best describes feedback control in enzyme regulation?

Accepted Answer

The product of a pathway inhibits the first enzyme in the pathway.

Question 16

Which enzyme class catalyzes the hydrolysis of peptide bonds in proteins?

Accepted Answer

Protease (Hydrolase)

Question 17

Which of the following is a fat-soluble vitamin that is essential for blood clotting?

Accepted Answer

Vitamin K

Question 18

Which of the following statements about zymogens is correct?

Accepted Answer

Zymogens are inactive precursors that require a chemical change to become active.

Question 19

Which of the following amino acids is most likely to stabilize the aromatic ring of phenylalanine in the hydrophobic pocket of chymotrypsin?

Accepted Answer

Leucine

Question 20

Which of the following best describes the effect of increasing substrate concentration on the rate of an enzyme-catalyzed reaction when the enzyme is not saturated?

Accepted Answer

The reaction rate increases directly with substrate concentration.

Enzymes and Vitamins: Structure, Function, and Regulation

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