chapter 13 section 4

Question 1

What are the two main types of enzyme inhibition?

Answer 1

Reversible and irreversible.

Question 2

How do reversible inhibitors interact with enzymes?

Answer 2

Through noncovalent association/dissociation.

Question 3

How do irreversible inhibitors act?

Answer 3

By forming covalent bonds with enzyme side chains or prosthetic groups.

Question 4

What is the consequence of irreversible inhibition?

Answer 4

A decrease in the concentration of active enzyme

Question 5

What are the three main types of reversible enzyme inhibition?

Answer 5

Competitive, noncompetitive, and uncompetitive.

Question 6

What characterizes competitive inhibition?

Answer 6

Substrate and inhibitor compete for the same active site; high [S] can overcome inhibition.

Question 7

What is the effect of competitive inhibition on Vmax and Km?

Answer 7

Vmax unchanged; Km increases

Question 8

What characterizes noncompetitive inhibition?

Answer 8

Inhibitor binds to enzyme at a site different from substrate; cannot be overcome by high [S].

Question 9

What is the effect of pure noncompetitive inhibition on Vmax and Km?

Answer 9

Vmax decreases; Km unchanged.

Question 10

What is mixed noncompetitive inhibition?

Answer 10

Inhibitor binding affects substrate binding both Vmax and Km change.

Question 11

What characterizes uncompetitive inhibition?

Answer 11

Inhibitor binds only to ES complex, preventing product release.

Question 12

What is the effect of uncompetitive inhibition on Vmax and Km?

Answer 12

Both decrease, but Km/Vmax ratio stays constant (parallel Lineweaver–Burk lines).

Question 13

Give a classic example of competitive inhibition.

Answer 13

Malonate inhibiting succinate dehydrogenase.

Question 14

Why do competitive inhibitors often resemble substrates structurally?

Answer 14

Because they bind at the same active site as the substrate.

Question 15

What distinguishes irreversible enzyme inhibition from reversible inhibition?

Answer 15

Irreversible inhibitors form covalent bonds with the enzyme, permanently inactivating it, while reversible inhibitors bind noncovalently and can dissociate.

Question 16

Why does irreversible inhibition resemble noncompetitive inhibition in kinetics?

Answer 16

lower apparent Vmax

Question 17

What are suicide substrates (mechanism-based inhibitors)?

Answer 17

Substrate analogs enzyme processes that covalently binds and inactivates the enzyme.

Question 17

How can irreversible inhibition be experimentally distinguished from reversible inhibition?

Answer 17

in irreversible inhibition enzyme activity decreases over time

Question 18

Why are suicide substrates also called “Trojan horse substrates”?

Answer 18

They mimic normal substrates, bind specifically, and then irreversibly trap the enzyme by covalent modification.

Question 19

How does penicillin act as a suicide substrate?

Answer 19

Its β-lactam ring reacts with a serine in the active site of glycopeptide transpeptidase, blocking bacterial cell wall synthesis

Question 20

What is the effect of penicillin binding on bacteria?

Answer 20

weakening the cell wall and causing bacterial lysis.