Question 1

Which of the following best explains why ATP, despite having a negative $$\Delta G$$ for hydrolysis, remains stable in water for several days?

Accepted Answer

The activation energy ($$E_A) $$barrier for ATP hydrolysis is high, preventing rapid reaction.

Question 2

A cell needs to catalyze a reaction that is thermodynamically feasible but proceeds very slowly. Which strategy would a cell use to increase the reaction rate?

Accepted Answer

Add a catalyst to lower the activation energy ($$E_A) $$required for the reaction.

Question 3

Which property is shared by all biological catalysts (enzymes)?

Accepted Answer

They increase reaction rates by lowering the activation energy ($$E_A).$$

Question 4

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

Accepted Answer

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

Question 5

A patient is exposed to a nerve gas that irreversibly inhibits acetylcholinesterase. What is the molecular basis for the toxicity?

Accepted Answer

The inhibitor binds covalently to the enzyme, causing permanent loss of catalytic activity.

Question 6

Which of the following statements about enzyme specificity is correct?

Accepted Answer

Enzymes have high substrate specificity due to the shape and chemistry of their active sites.

Question 7

Which class of enzyme catalyzes the transfer of functional groups from one molecule to another?

Accepted Answer

Transferases

Question 8

A researcher observes that an enzyme's activity is highest at pH 2.0 and drops sharply at higher pH. Which enzyme is most likely being studied?

Accepted Answer

Pepsin

Question 9

Which of the following best describes the induced-fit model of enzyme action?

Accepted Answer

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

Question 10

Which mechanism of substrate activation involves the enzyme making a bond in the substrate more susceptible to catalytic attack?

Accepted Answer

Bond distortion

Question 11

A competitive inhibitor affects enzyme activity by:

Accepted Answer

Binding to the active site and competing with the substrate.

Question 12

Which statement about enzyme regulation by phosphorylation is correct?

Accepted Answer

Phosphorylation can either activate or inhibit enzymes, depending on the enzyme.

Question 13

Which of the following is a property of allosteric enzymes?

Accepted Answer

They are regulated by molecules binding to a site distinct from the active site.

Question 14

A scientist discovers an RNA molecule that catalyzes the cleavage of another RNA. This molecule is best described as:

Accepted Answer

A ribozyme

Question 15

Which of the following is NOT a major class of enzyme according to the Enzyme Commission (EC)?

Accepted Answer

Polymerases

Question 16

Feedback inhibition in a metabolic pathway typically involves:

Accepted Answer

The final product inhibiting the first enzyme in the pathway.

Question 17

Which statement about enzyme-catalyzed reactions is correct?

Accepted Answer

Enzymes change the rate at which equilibrium is achieved, but not the position of equilibrium.

Question 18

A patient with vitamin deficiency is found to have reduced activity of several enzymes. This is most likely due to:

Accepted Answer

Lack of prosthetic groups, which are often derived from vitamins and required for enzyme activity.

Question 19

Which of the following factors can affect enzyme activity by disrupting hydrogen bonding and ionic interactions needed for tertiary conformation?

Accepted Answer

Changes in ionic strength of the environment

Question 20

Which of the following is true regarding the effect of temperature on enzyme activity in homeotherms?

Accepted Answer

Enzyme activity is maximal at 37°C, and most enzymes are inactivated above 50–55°C.

Chapter 6: Enzymes – The Catalysts of Life (Cell Biology Study Notes)

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