Question 1

Which of the following best describes the role of the catalytic triad in serine proteases such as chymotrypsin?

Accepted Answer

It facilitates nucleophilic attack on the peptide bond by activating Ser-195 through a relay involving His-57 and Asp-102.

Question 2

Which equation correctly represents the hydrolysis of a peptide bond by a serine protease?

Accepted Answer

$$\mathrm{R_1$-CONH-R_2$} + H_2O \rightarrow \mathrm{R_1$-COOH} + \mathrm{R_2$-NH_2$}$$

Question 3

What is the function of the oxyanion hole in the mechanism of serine proteases?

Accepted Answer

It stabilizes the negative charge on the tetrahedral intermediate during peptide bond cleavage.

Question 4

Which of the following statements about zymogens is TRUE?

Accepted Answer

Zymogens are inactive precursors that require proteolytic cleavage to become active enzymes.

Question 5

Trypsin is able to activate other protease zymogens in the digestive tract. Which process initiates the activation of trypsin itself?

Accepted Answer

Cleavage by enterokinase (enteropeptidase) at the N-terminal region.

Question 6

Which amino acid acts as the nucleophile in the catalytic mechanism of serine proteases?

Accepted Answer

Serine

Question 7

The specificity of serine proteases such as trypsin, chymotrypsin, and elastase is primarily determined by:

Accepted Answer

The size and composition of the S1 binding pocket.

Question 8

Which of the following correctly matches the protease with its S1 pocket specificity?

Accepted Answer

Elastase: small, nonpolar residues such as Ala and Gly

Question 9

Which of the following is a correct description of the catalytic triad in chymotrypsin?

Accepted Answer

Ser-195, His-57, Asp-102

Question 10

Which class of proteases uses a metal ion, typically Zn$$^{2+}$$, to activate water for nucleophilic attack?

Accepted Answer

Metalloproteases

Question 11

During the catalytic mechanism of chymotrypsin, which intermediate is formed after nucleophilic attack by Ser-195?

Accepted Answer

A tetrahedral intermediate stabilized by the oxyanion hole

Question 12

Which of the following statements about irreversible inhibitors of serine proteases is CORRECT?

Accepted Answer

They covalently modify catalytically important residues such as Ser or His.

Question 13

Which of the following best explains why the pKa of His-57 in the catalytic triad shifts from 7 to 12 when substrate binds?

Accepted Answer

Asp-102 modulates the protonation state of His-57, increasing its basicity.

Question 14

Which of the following is NOT a biological function of proteases?

Accepted Answer

DNA replication

Question 15

A mutation that replaces Ser-195 with alanine in chymotrypsin would most likely result in:

Accepted Answer

Loss of catalytic activity due to absence of the nucleophile.

Question 16

Which of the following best describes the difference between endoproteases and exoproteases?

Accepted Answer

Endoproteases cleave internal peptide bonds, while exoproteases cleave terminal amino acids.

Question 17

Which of the following is a correct sequence of events in the activation of digestive zymogens?

Accepted Answer

Enteropeptidase cleaves trypsinogen to form trypsin, which then activates other zymogens.

Question 18

Which of the following statements about the S1 pocket of chymotrypsin is TRUE?

Accepted Answer

It is deep and hydrophobic, favoring aromatic residues such as Phe, Tyr, and Trp.

Question 19

Which of the following is a correct description of the role of Asp-102 in the catalytic triad of serine proteases?

Accepted Answer

Asp-102 stabilizes the positive charge on His-57, increasing its ability to accept a proton from Ser-195.

Serine Proteases and Enzyme Mechanisms: Structure, Function, and Catalysis

Study Guide - Practice Questions