Question 1

Which of the following best explains how enzymes increase the rate of a chemical reaction?

Accepted Answer

By lowering the activation energy by stabilizing the transition state more than the substrate

Question 2

A reaction coordinate diagram for an enzyme-catalyzed reaction shows a lower peak for the transition state compared to the uncatalyzed reaction. What does this indicate?

Accepted Answer

The enzyme decreases the activation energy required for the reaction

Question 3

Which of the following statements about the proximity effect in enzyme catalysis is correct?

Accepted Answer

It describes how enzymes increase reaction rates by bringing reactants together in the correct orientation

Question 4

Which model of substrate binding involves a conformational change in the enzyme upon substrate binding?

Accepted Answer

Induced-fit model

Question 5

Which amino acid is NOT typically part of the catalytic triad in serine proteases?

Accepted Answer

Glutamate

Question 6

In the mechanism of chymotrypsin, what is the role of the 'oxyanion hole'?

Accepted Answer

It stabilizes the negative charge on the tetrahedral intermediate during catalysis

Question 7

Which of the following best describes a transition state analog?

Accepted Answer

A molecule that resembles the transition state and binds strongly to the enzyme, acting as an inhibitor

Question 8

Which of the following amino acids is most likely to act as a general base in enzyme catalysis at pH 7?

Accepted Answer

Histidine

Question 9

During the chymotrypsin reaction mechanism, which step involves the formation of a covalent acyl-enzyme intermediate?

Accepted Answer

Step 3: Collapse of the tetrahedral intermediate and peptide bond cleavage

Question 10

Which of the following best explains why chymotrypsin cannot act as a ligase to join two peptides together?

Accepted Answer

The products of hydrolysis have higher free energy than the reactants, making the reverse reaction unfavorable

Question 11

Trypsin, chymotrypsin, and elastase are all serine proteases. What accounts for their different substrate specificities?

Accepted Answer

Differences in the size and charge of their substrate binding pockets

Question 12

Which of the following reactions is most likely to involve a nucleophilic attack by a carbanion stabilized by a carbonyl group?

Accepted Answer

Aldol condensation

Question 13

A mutation replaces Ser195 with Ala in chymotrypsin. What is the most likely effect on enzyme activity?

Accepted Answer

Enzyme activity will decrease because Ala cannot act as a nucleophile

Question 14

Which of the following best describes the effect of pH on the activity of an enzyme with two ionizable groups in its active site?

Accepted Answer

Activity will show a maximum between the pKa values of the two groups

Question 15

Which of the following is a correct statement about covalent catalysis in enzyme mechanisms?

Accepted Answer

A covalent intermediate is formed and then broken to regenerate the enzyme

Question 16

Which of the following equations correctly represents the change in activation free energy for an enzyme-catalyzed reaction?

Accepted Answer

$$\Delta G_{ES ightarrow ES$$^{\ddagger}$$} \u003c \Delta G_{S ightarrow S$$^{\ddagger}$$}$$

Question 17

Which of the following is a real-world application of transition state analogs?

Accepted Answer

They are used as potent enzyme inhibitors in drug design

Question 18

In the catalytic mechanism of chymotrypsin, which residue acts as a general base to activate Ser195 for nucleophilic attack?

Accepted Answer

His57

Question 19

Which of the following best describes the specificity of elastase compared to chymotrypsin and trypsin?

Accepted Answer

Elastase cleaves after small amino acids such as Gly and Ala

Question 20

A patient is given a drug that is a transition state analog for a key metabolic enzyme. What is the expected effect?

Accepted Answer

The enzyme will be inhibited due to strong binding of the analog

Enzyme Mechanisms: Catalysis, Transition State Stabilization, and Specificity

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