Question 1

Which of the following best describes the role of the Ser-His-Asp catalytic triad in chymotrypsin's mechanism?

Accepted Answer

It generates a powerful nucleophile by activating the serine residue for attack on the peptide carbonyl group.

Question 2

Which catalytic strategy involves the enzyme forming a temporary covalent bond with the substrate?

Accepted Answer

Covalent catalysis

Question 3

A competitive inhibitor affects enzyme kinetics by:

Accepted Answer

Increasing $$K_M$$ and leaving $$V_{max}$$ unchanged

Question 4

Which of the following statements about organophosphates such as sarin is correct?

Accepted Answer

They covalently modify the active site serine residue, irreversibly inhibiting acetylcholinesterase.

Question 5

Atropine is used as an antidote for sarin poisoning because:

Accepted Answer

It binds to acetylcholine receptors, preventing acetylcholine from activating them.

Question 6

Which of the following amino acids is preferred by chymotrypsin due to its large hydrophobic side chain?

Accepted Answer

Tryptophan

Question 7

In a double reciprocal (Lineweaver-Burk) plot, how does the presence of a competitive inhibitor affect the plot compared to no inhibitor?

Accepted Answer

The lines intersect at the y-axis, indicating unchanged $$V_{max}$$ but increased $$K_M.$$

Question 8

Which of the following is NOT a common catalytic strategy used by enzymes?

Accepted Answer

Allosteric catalysis

Question 9

Why is pyridostigmine administered in cases of potential sarin exposure?

Accepted Answer

It acts as a reversible competitive inhibitor, protecting the enzyme from irreversible inhibition by sarin.

Question 10

Which of the following best explains the stabilization of the tetrahedral intermediate in chymotrypsin catalysis?

Accepted Answer

Interaction with peptide NH groups in the oxyanion hole

Question 11

Which statement about uncompetitive inhibition is correct?

Accepted Answer

The inhibitor binds only to the enzyme-substrate complex, decreasing both $$V_{max}$$ and $$K_M.$$

Question 12

Which of the following is a real-world consequence of acetylcholinesterase inhibition by sarin gas?

Accepted Answer

Excessive muscle stimulation, increased secretions, and potentially fatal paralysis

Question 13

Which of the following molecules is structurally similar to the R group of tryptophan and acts as a competitive inhibitor of chymotrypsin?

Accepted Answer

Indole

Question 14

Which equation correctly represents the Michaelis-Menten relationship for enzyme kinetics?

Accepted Answer

$$v = \frac{V_{max}[S]}{K_M + [S]}$$

Question 15

Which of the following is true regarding the effect of temperature on enzyme activity?

Accepted Answer

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

Question 16

Which of the following is a plausible effect of a metal ion in enzyme catalysis?

Accepted Answer

It stabilizes negative charges and can help orient substrates for reaction.

Question 17

Which of the following best describes catalysis by approximation and orientation?

Accepted Answer

The enzyme brings substrates into close proximity and aligns them to facilitate the reaction.

Question 18

If an enzyme is exposed to a covalent inhibitor, which of the following is most likely to occur?

Accepted Answer

The enzyme will be irreversibly inhibited due to covalent modification at the active site.

Question 19

Which of the following is a correct statement about the oxyanion hole in chymotrypsin?

Accepted Answer

It is a region that stabilizes the negative charge on the tetrahedral intermediate's carbonyl oxygen.

Biochemistry: A Short Course 8

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