Question 1

Which of the following best describes a competitive inhibitor's effect on enzyme kinetics?

Accepted Answer

It increases $$K_m$$ but does not change $$V_{max}.$$

Question 2

A pharmaceutical company develops a drug that covalently modifies the serine residue in the active site of acetylcholinesterase. What type of inhibitor is this drug?

Accepted Answer

Group-specific reagent

Question 3

Which statement about irreversible inhibitors is correct?

Accepted Answer

They form covalent or extremely tight noncovalent bonds with the enzyme.

Question 4

Methotrexate is a drug that inhibits dihydrofolate reductase (DHFR). When NADPH concentration is varied, methotrexate shows uncompetitive inhibition. What does this imply about its binding?

Accepted Answer

Methotrexate binds only to the ES complex.

Question 5

Which of the following is a mechanism-based (suicide) inhibitor?

Accepted Answer

A substrate-like molecule that is modified by the enzyme and then covalently attaches, inactivating the enzyme.

Question 6

In a Lineweaver-Burk plot, which pattern is characteristic of uncompetitive inhibition?

Accepted Answer

Lines are parallel, both $$V_{max}$$ and $$K_m$$ decrease.

Question 7

A transition state analog is most likely to act as which type of inhibitor?

Accepted Answer

Competitive inhibitor, but can also be irreversible

Question 8

Which equation represents the dissociation constant ($$K_i) $$for a reversible inhibitor binding to an enzyme?

Accepted Answer

$$K_i = \frac{[E][I]}{[EI]}$$

Question 9

Which of the following best describes noncompetitive inhibition?

Accepted Answer

The inhibitor binds equally well to E and ES, decreasing $$V_{max}$$ but not changing $$K_m.$$

Question 10

A patient is treated with a drug that acts as an affinity label for a protease. What is the most likely mechanism of action?

Accepted Answer

The drug covalently modifies a specific amino acid residue in the active site, inactivating the enzyme.

Question 11

Which of the following is true regarding mixed inhibition?

Accepted Answer

The inhibitor binds to both E and ES, affecting both $$K_m$$ and $$V_{max}.$$

Question 12

If the addition of an inhibitor causes a twofold increase in apparent $$K_m$$ but no change in $$V_{max}$$, what type of inhibition is occurring?

Accepted Answer

Competitive inhibition

Question 13

Which of the following drugs is an example of a mechanism-based (suicide) inhibitor used in the treatment of depression and Parkinson's disease?

Accepted Answer

MAO inhibitors

Question 14

What is the effect of an uncompetitive inhibitor on the apparent $$K_m$$ and $$V_{max} of an $$enzyme?

Accepted Answer

Both $$K_m$$ and $$V_{max}$$ decrease.

Question 15

Which of the following is NOT a class of irreversible inhibitor?

Accepted Answer

Uncompetitive inhibitor

Question 16

A new HIV protease inhibitor is designed to mimic the tetrahedral intermediate of peptide bond hydrolysis. What type of inhibitor is this?

Accepted Answer

Transition state analog

Question 17

Which of the following statements about reversible inhibitors is correct?

Accepted Answer

They bind and release rapidly, and inhibition is thermodynamically controlled.

Question 18

Which parameter is used to measure the potency of an inhibitor in enzyme kinetics?

Accepted Answer

$$K_i$$

Question 19

Which of the following best explains why transition state analogs are effective enzyme inhibitors?

Accepted Answer

They bind to the enzyme more tightly than the substrate by mimicking the transition state.

Question 20

Which of the following is a real-world example of a group-specific reagent used as an irreversible inhibitor?

Accepted Answer

Iodoacetamide modifying cysteine residues

Enzyme Inhibition: Types, Mechanisms, and Kinetics

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