Q: Which of the following equations best represents the general catalytic mechanism of serine proteases?

$$\text{Ser-OH} + \text{Peptide} \rightarrow \text{Ser-O-Peptide} \rightarrow \text{Ser-OH} + \text{Cleaved Peptide}$$

Question 1

Which of the following best explains why chymotrypsin, trypsin, and elastase have different substrate specificities despite sharing the same catalytic triad?

Accepted Answer

Differences in the residues forming the specificity pocket

Question 2

Which amino acid is directly involved as the nucleophile in the catalytic mechanism of serine proteases?

Accepted Answer

Serine

Question 3

Trypsin preferentially cleaves peptide bonds after which types of amino acid residues?

Accepted Answer

Lysine and Arginine

Question 4

Which evolutionary process describes the origin of chymotrypsin, trypsin, and elastase from a common ancestral protease?

Accepted Answer

Divergent evolution

Question 5

What is the role of the oxyanion hole in serine proteases?

Accepted Answer

Stabilizes the negatively charged transition state during catalysis

Question 6

Which of the following statements about convergent evolution in proteases is correct?

Accepted Answer

Unrelated enzymes evolve similar catalytic mechanisms independently

Question 7

Which of the following is a cysteine protease and is commonly used as a meat tenderizer?

Accepted Answer

Papain

Question 8

In the catalytic mechanism of cysteine proteases, which residue acts as the nucleophile?

Accepted Answer

Cysteine

Question 9

Aspartyl proteases, such as pepsin and HIV protease, utilize which catalytic residues in their active site?

Accepted Answer

Two aspartate residues

Question 10

Which of the following best describes the mechanism of metalloproteases such as thermolysin?

Accepted Answer

A metal ion stabilizes a hydroxide nucleophile that attacks the peptide bond

Question 11

Which of the following drugs acts as a transition-state analog inhibitor of HIV protease?

Accepted Answer

Ritonavir

Question 12

The catalytic triad in serine proteases consists of which three amino acids?

Accepted Answer

Serine, histidine, and aspartate

Question 13

Which of the following best explains why HIV protease inhibitors are effective in treating HIV infection?

Accepted Answer

They mimic the transition state of the substrate, preventing protease activity

Question 14

Which of the following equations best represents the general catalytic mechanism of serine proteases?

Accepted Answer

$$	ext{Ser-OH} + 	ext{Peptide} ightarrow 	ext{Ser-O-Peptide} ightarrow 	ext{Ser-OH} + 	ext{Cleaved Peptide}$$

Question 15

Which structural feature of elastase accounts for its preference for small, nonpolar amino acid substrates?

Accepted Answer

A small specificity pocket formed by bulky side chains

Question 16

Which of the following is NOT a serine protease?

Accepted Answer

Pepsin

Question 17

A mutation replaces the aspartate residue in the trypsin specificity pocket with a neutral amino acid. What is the most likely effect?

Accepted Answer

Reduced specificity for positively charged residues

Question 18

Which of the following best describes the role of gene duplication in the evolution of serine proteases?

Accepted Answer

It allows for the creation of new enzymes with distinct substrate specificities

Question 19

Which of the following proteases utilizes a catalytic zinc ion to facilitate peptide bond hydrolysis?

Accepted Answer

Thermolysin

Question 20

Which of the following statements about the catalytic mechanism of aspartyl proteases is correct?

Accepted Answer

One aspartate acts as a general base to activate water, while the other stabilizes the transition state

Protease Mechanisms, Specificity, and Evolution

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