Question 1

Which of the following best describes covalent catalysis as used by enzymes?

Accepted Answer

Enzyme forms a transient covalent bond with the substrate, which is later broken to regenerate the enzyme.

Question 2

An enzyme has two key catalytic residues, Glu 39 ($pK_a = 5.9$) and Asp 52 ($pK_a = 4.1$). Which of the following is most likely about their mechanism if the pH of the solution is $pH = 5.2$?

Accepted Answer

Glu 39 is more likely to be protonated than Asp 52.

Question 3

Which of the following mechanisms is NOT used by enzymes for catalysis?

Accepted Answer

Using mechanical force to break substrate bonds

Question 4

Which catalytic mechanism involves the enzyme acting as a nucleophile to form a covalent intermediate with the substrate?

Accepted Answer

Covalent catalysis

Question 5

Which of the following is a key feature of covalent catalysis?

Accepted Answer

A transient covalent bond is formed between enzyme and substrate.

Question 6

If an enzyme catalyzes a reaction using both acid-base and covalent catalysis, which of the following statements is most accurate?

Accepted Answer

The enzyme forms a covalent intermediate and also donates or accepts protons during the reaction.

Question 7

Which of the following would most likely increase the reaction rate of an enzyme-catalyzed reaction involving covalent catalysis?

Accepted Answer

Decreasing the activation energy for formation and breakdown of the covalent intermediate.

Question 8

A mutation in an enzyme changes a catalytic serine to alanine. The enzyme previously used covalent catalysis. What is the most likely effect?

Accepted Answer

The enzyme will lose the ability to form a covalent intermediate, reducing its catalytic efficiency.

Question 9

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

Accepted Answer

Thermal catalysis

Question 10

If the $pK_a$ of a catalytic residue is 6.0 and the reaction occurs at $pH = 7.0$, what is the likely protonation state of the residue?

Accepted Answer

Mostly deprotonated

Question 11

Which of the following best explains why covalent catalysis can increase the rate of a chemical reaction?

Accepted Answer

It provides an alternative reaction pathway with a lower activation energy.

Question 12

Which of the following is a plausible reason why an enzyme might use both acid-base and covalent catalysis in a single reaction?

Accepted Answer

To stabilize different intermediates and facilitate multiple steps in the reaction.

Question 13

A reaction catalyzed by an enzyme involves the formation of a covalent bond between the enzyme and substrate, followed by hydrolysis to release the product. Which catalytic strategy is primarily being used?

Accepted Answer

Covalent catalysis

Question 14

Which of the following statements about enzyme catalysis is FALSE?

Accepted Answer

Enzymes always form permanent covalent bonds with substrates.

Question 15

Which of the following is most likely to occur if the $pH$ of the environment is much lower than the $pK_a$ of a catalytic residue involved in acid-base catalysis?

Accepted Answer

The residue will be mostly protonated.

Covalent Catalysis and Enzyme Mechanisms: Study Notes

Study Guide - Practice Questions

Study Guide - Flashcards