Question 1

Which of the following best describes the effect of an enzyme on the activation energy ($E_a$) of a biochemical reaction?

Accepted Answer

It decreases the activation energy by stabilizing the transition state.

Question 2

According to the induced fit model of enzyme catalysis, what happens when a substrate binds to an enzyme?

Accepted Answer

The enzyme undergoes a conformational change that increases its affinity for the transition state.

Question 3

Which of the following statements about competitive inhibition is correct?

Accepted Answer

A competitive inhibitor increases the apparent $K_M$ but does not affect $V_{max}$.

Question 4

In the serine protease catalytic triad, which amino acid acts as the nucleophile that attacks the peptide bond?

Accepted Answer

Serine

Question 5

Which of the following best explains why enzymes are highly specific for their substrates?

Accepted Answer

Enzymes have active sites that are complementary in shape and chemical properties to their substrates.

Question 6

A mutation in an enzyme causes the $pK_a$ of a histidine residue in the active site to shift from 6.0 to 8.0. What is the most likely effect on enzyme activity at physiological pH (7.4)?

Accepted Answer

The enzyme will be more active because the histidine will be more likely to be protonated.

Question 7

Which of the following is a correct statement about the Michaelis-Menten constant ($K_M$)?

Accepted Answer

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

Question 8

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

Accepted Answer

It decreases $V_{max}$ but does not change $K_M$.

Question 9

Which of the following amino acids is most likely to participate in acid-base catalysis at physiological pH due to its side chain $pK_a$?

Accepted Answer

Histidine

Question 10

A patient is given a drug that acts as a mechanism-based (suicide) inhibitor of an enzyme. Which of the following best describes how this inhibitor works?

Accepted Answer

It is converted by the enzyme into a reactive form that irreversibly inactivates the enzyme.

Question 11

Which of the following best explains why the presence of Mg$^{2+}$ is required for kinase activity with ATP as a substrate?

Accepted Answer

Mg$^{2+}$ binds to ATP, reducing the negative charge and making the phosphates more susceptible to nucleophilic attack.

Question 12

Which of the following statements about feedback inhibition in metabolic pathways is correct?

Accepted Answer

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

Question 13

Which of the following is a correct description of the difference between an apoenzyme and a holoenzyme?

Accepted Answer

An apoenzyme is the protein part of an enzyme without its cofactor; a holoenzyme is the complete, active enzyme with its cofactor.

Question 14

Which of the following best describes the role of the 'oxyanion hole' in serine proteases?

Accepted Answer

It stabilizes the negative charge on the tetrahedral intermediate during catalysis.

Question 15

Which of the following is true regarding the effect of pH on enzyme activity, as illustrated by the titration curve for aspartic acid?

Accepted Answer

Enzyme activity is highest when the side chain is in the acid (protonated) form.

Question 16

Which of the following statements about the lock-and-key and induced fit models of enzyme action is correct?

Accepted Answer

The lock-and-key model suggests the enzyme is rigid, while the induced fit model suggests the enzyme changes shape upon substrate binding.

Question 17

Which of the following best describes the effect of an uncompetitive inhibitor on enzyme kinetics?

Accepted Answer

It decreases both $K_M$ and $V_{max}$ by the same factor.

Question 18

Which of the following amino acids is most likely to be found in the active site of an enzyme that catalyzes covalent acyl group transfer reactions?

Accepted Answer

Cysteine

Question 19

Which of the following is a real-world example of enzyme regulation by allosteric activation?

Accepted Answer

Accumulation of substrate A induces activation of the enzyme that converts A to B, increasing pathway flux.

Enzyme Catalysis and Carbohydrate Structure: Key Concepts in Biochemistry

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