Question 1

Which of the following best describes the role of enzymes in cellular reactions?

Accepted Answer

Enzymes increase the rate of reaction by lowering the activation energy required.

Question 2

A cell is exposed to a competitive inhibitor for an essential enzyme. Which of the following would most likely restore enzyme activity?

Accepted Answer

Increasing the concentration of the substrate.

Question 3

Which amino acids are most commonly found in the active sites of enzymes and participate in catalysis?

Accepted Answer

Cysteine, histidine, serine, aspartate, glutamate, and lysine

Question 4

Which of the following statements about the induced-fit model of enzyme action is correct?

Accepted Answer

Substrate binding induces a conformational change in the enzyme, optimizing catalysis.

Question 5

A patient is diagnosed with lead poisoning. Lead acts as an irreversible inhibitor for certain enzymes. What is the most likely effect of lead on these enzymes?

Accepted Answer

Lead binds covalently, causing permanent loss of enzyme activity.

Question 6

Which enzyme class is responsible for catalyzing the transfer of functional groups from one molecule to another?

Accepted Answer

Transferases

Question 7

The rate of an enzyme-catalyzed reaction increases with temperature up to a point, after which it decreases. What is the most likely explanation for the decrease in rate at high temperatures?

Accepted Answer

The enzyme denatures, losing its three-dimensional structure and active site.

Question 8

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

Accepted Answer

The shape and chemistry of the active site allow only certain substrates to bind.

Question 9

Which mechanism of substrate activation involves the enzyme distorting the substrate's bonds to make them more susceptible to catalytic attack?

Accepted Answer

Bond distortion

Question 10

A scientist discovers an enzyme that requires a tightly bound metal ion for activity. This metal ion is best described as:

Accepted Answer

A prosthetic group

Question 11

Which of the following equations correctly represents the relationship between the rate of a reaction and the fraction of molecules with energy equal to or greater than the activation energy $$E_A$$?

Accepted Answer

Rate $$\propto \exp\left(-\frac{E_A}{RT}\right)$$

Question 12

Which of the following is an example of feedback inhibition in a metabolic pathway?

Accepted Answer

The final product of a pathway inhibits an earlier enzyme in the pathway.

Question 13

Which statement about ribozymes is correct?

Accepted Answer

Ribozymes are RNA molecules with catalytic activity.

Question 14

Which of the following best describes the effect of a noncompetitive inhibitor on enzyme activity?

Accepted Answer

It binds to a site other than the active site and reduces catalytic activity.

Question 15

Glycogen phosphorylase is regulated by phosphorylation and dephosphorylation. Which enzyme catalyzes the removal of phosphate groups from glycogen phosphorylase?

Accepted Answer

Protein phosphatase

Question 16

Which of the following statements about allosteric regulation is correct?

Accepted Answer

Allosteric effectors bind to a regulatory site, stabilizing either the high- or low-affinity conformation.

Question 17

A proteolytic enzyme is synthesized in an inactive form and activated by cleavage. This process is known as:

Accepted Answer

Proteolytic cleavage

Question 18

Which of the following best explains why heat is not a useful method for increasing reaction rates in cells?

Accepted Answer

Cells are isothermal and cannot tolerate large temperature changes.

Question 19

Which of the following is a common mechanism by which enzymes activate substrates for catalysis?

Accepted Answer

Bond distortion, proton transfer, and electron transfer

Question 20

A researcher is studying an enzyme that exhibits positive cooperativity. Which of the following best describes this phenomenon?

Accepted Answer

Binding of substrate to one catalytic site increases the affinity of other sites for substrate.

Enzymes: The Catalysts of Life – Study Notes

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