Question 1

Which amino acid acts as the nucleophile in the catalytic triad of serine proteases during peptide bond hydrolysis?

Accepted Answer

Serine

Question 2

During the mechanism of serine proteases, what is the primary role of the histidine residue in the catalytic triad?

Accepted Answer

Acts as a general base to accept a proton from serine

Question 3

In the serine protease mechanism, what is the function of the 'oxyanion hole'?

Accepted Answer

It stabilizes the negative charge on the tetrahedral intermediate

Question 4

Which of the following best describes the acyl-enzyme intermediate in serine protease catalysis?

Accepted Answer

A covalent bond between the substrate's carbonyl carbon and the serine residue

Question 5

Which step in the serine protease mechanism involves water acting as a nucleophile?

Accepted Answer

Hydrolysis of the acyl-enzyme intermediate

Question 6

A mutation replaces the serine in the catalytic triad of a serine protease with alanine. What is the most likely effect on enzyme activity?

Accepted Answer

The enzyme will lose its ability to form the acyl-enzyme intermediate

Question 7

Which of the following correctly orders the steps in the serine protease mechanism?

Accepted Answer

Substrate binding → nucleophilic attack by serine → formation of tetrahedral intermediate → collapse to acyl-enzyme intermediate → nucleophilic attack by water → second tetrahedral intermediate → product release

Question 8

If the histidine residue in the catalytic triad is mutated to lysine, what is the most likely effect on the enzyme's catalytic mechanism?

Accepted Answer

The enzyme will be unable to deprotonate serine efficiently

Question 9

Which of the following equations best represents the general reaction catalyzed by serine proteases?

Accepted Answer

$$\mathrm{R_1$-CO-NH-R_2$ + H_2O \rightarrow R_1$-COOH + H_2N-R_2$}$$

Question 10

A patient has a genetic mutation that reduces the ability of their serine proteases to stabilize the oxyanion intermediate. Which of the following is the most likely biochemical consequence?

Accepted Answer

Decreased rate of peptide bond hydrolysis

Question 11

In the context of serine protease catalysis, what is the significance of the tetrahedral intermediate?

Accepted Answer

It is a high-energy transition state stabilized by the oxyanion hole

Question 12

Which of the following best explains why serine proteases are highly specific for certain peptide bonds?

Accepted Answer

The enzyme's substrate-binding pocket accommodates specific side chains

Question 13

A researcher adds a competitive inhibitor that mimics the transition state of the substrate to a serine protease reaction. What is the most likely effect?

Accepted Answer

The enzyme's activity will decrease due to transition state stabilization by the inhibitor

Question 14

Which of the following statements about the hydrolysis of the acyl-enzyme intermediate in serine proteases is correct?

Accepted Answer

It is catalyzed by a nucleophilic attack from water, activated by histidine

Question 15

Which of the following best describes the role of aspartate in the catalytic triad of serine proteases?

Accepted Answer

It stabilizes the positive charge on histidine, enhancing its basicity

Question 16

A serine protease is incubated with a peptide substrate and a molecule of D2O (heavy water) instead of H2O. Which atom in the product is most likely to incorporate deuterium?

Accepted Answer

The oxygen atom of the carboxyl group in the product

Question 17

Which of the following would most likely result if the oxyanion hole of a serine protease were mutated to remove its hydrogen-bonding capability?

Accepted Answer

The tetrahedral intermediate would be less stable, decreasing catalytic efficiency

Question 18

Which of the following best explains why serine proteases do not hydrolyze all peptide bonds indiscriminately in the cell?

Accepted Answer

Their active sites are highly specific for certain amino acid sequences

Question 19

A patient is found to have a deficiency in serine protease activity. Which of the following physiological processes is most likely to be impaired?

Accepted Answer

Protein digestion in the small intestine

Mechanism of Serine Proteases: Catalytic Action and Intermediates

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