Question 1

Which of the following best explains why enzymes are more effective catalysts in biological systems compared to non-biological catalysts?

Accepted Answer

Enzymes are highly specific for their substrates and can be regulated by the cell.

Question 2

Which of the following statements about the activation energy ($$\Delta G$$^{\ddagger}$$) of a reaction is correct?

Accepted Answer

Enzymes lower the activation energy, allowing more reactant molecules to reach the transition state.

Question 3

Which of the following is NOT a major class of enzyme catalytic mechanisms?

Accepted Answer

Hydrophobic catalysis

Question 4

The catalytic triad of chymotrypsin consists of which three amino acids?

Accepted Answer

Serine, Histidine, Aspartate

Question 5

Refer to the following equation: $$\Delta G = G_{	ext{products}} - G_{	ext{reactants}}. If$$ $$\Delta G \u003c 0$$, what does this indicate about the reaction?

Accepted Answer

The reaction is spontaneous and will proceed in the forward direction.

Question 6

Which feature of enzyme active sites is best described by the induced fit model?

Accepted Answer

The active site undergoes a conformational change to better accommodate the substrate.

Question 7

Which of the following best describes the role of the oxyanion hole in chymotrypsin catalysis?

Accepted Answer

It stabilizes the negative charge on the transition state intermediate.

Question 8

A mutation replaces the Gly residue in the oxyanion hole of a bacterial protease with Asp. What is the most likely effect on enzyme activity?

Accepted Answer

Activity decreases due to electrostatic repulsion of the transition state.

Question 9

Which of the following is a correct example of covalent catalysis?

Accepted Answer

A nucleophilic amino acid side chain forming a transient covalent bond with the substrate.

Question 10

Which of the following amino acid side chains can act as a nucleophile in covalent catalysis when deprotonated?

Accepted Answer

Serine

Question 11

Which of the following best explains why enzymes are highly specific for their substrates?

Accepted Answer

The active site contains functional groups that precisely recognize and bind specific substrates.

Question 12

Which of the following is a key difference between the lock-and-key and induced fit models of enzyme action?

Accepted Answer

The induced fit model involves conformational changes in the enzyme upon substrate binding.

Question 13

Which of the following best describes the role of cofactors in enzyme catalysis?

Accepted Answer

Cofactors are non-protein molecules that assist in catalysis, sometimes by providing functional groups not found in amino acid side chains.

Question 14

Which of the following best explains why chymotrypsin, trypsin, and elastase have different substrate specificities?

Accepted Answer

They have different amino acid sequences in their specificity pockets.

Question 15

Which of the following is an example of convergent evolution in enzymes?

Accepted Answer

Chymotrypsin and subtilisin both having a Ser-His-Asp catalytic triad despite unrelated sequences.

Question 16

Why are zymogens important in the regulation of protease activity in the digestive system?

Accepted Answer

They allow proteases to be synthesized in an inactive form, preventing unwanted protein degradation.

Question 17

Which of the following best describes the effect of a protease inhibitor such as BPTI (Bovine Pancreatic Trypsin Inhibitor)?

Accepted Answer

It binds to the active site of trypsin and prevents further catalytic activity by mimicking a substrate but not being fully hydrolyzed.

Question 18

Which of the following is a real-world example of metal ion catalysis?

Accepted Answer

Zinc ion stabilizing the negative charge on the oxygen atom during the conversion of acetaldehyde to ethanol by alcohol dehydrogenase.

Question 19

Which of the following statements about the free energy diagram of a catalyzed versus uncatalyzed reaction is correct?

Accepted Answer

The presence of an enzyme lowers the activation energy ($$\Delta G$$^{\ddagger}$$) but does not change the overall free energy change ($$\Delta G$$) of the reaction.

How Enzymes Work: Mechanisms, Structure, and Evolution

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