Question 1

Which of the following best describes the role of an enzyme in a chemical reaction?

Accepted Answer

It lowers the activation energy $$\Delta G$$^{\ddagger}$$, thereby increasing the reaction rate.

Question 2

Which property distinguishes enzymes from most chemical catalysts used in organic chemistry labs?

Accepted Answer

Enzymes exhibit stereospecificity and regioselectivity under mild conditions.

Question 3

In the context of enzyme catalysis, what is the 'transition state'?

Accepted Answer

A high-energy, unstable configuration that determines the rate of the reaction.

Question 4

Which equation describes the rate constant $$k$$ for a reaction according to transition state theory?

Accepted Answer

$$k = \frac{k_B T}{h} e$$^{-\Delta G^{\ddagger}$$/RT}$$

Question 5

Which of the following statements about enzyme-catalyzed reactions is TRUE?

Accepted Answer

Enzymes increase reaction rates by stabilizing the transition state.

Question 6

Hexokinase catalyzes the reaction: ATP + glucose $$\rightarrow$$ ADP + glucose-6-phosphate. Why is this reaction possible in cells?

Accepted Answer

Because the enzyme couples the favorable hydrolysis of ATP to the phosphorylation of glucose.

Question 7

Which of the following is NOT a strategy enzymes use to accelerate reactions?

Accepted Answer

Preferential binding to the ground state of the substrate.

Question 8

Apoenzyme and holoenzyme differ in that:

Accepted Answer

Holoenzyme is the complete, active enzyme with its cofactor or coenzyme bound.

Question 9

Which of the following best explains why enzymes can be regulated?

Accepted Answer

Enzymes have specific active sites that can interact with regulatory molecules.

Question 10

Which of the following is a consequence of enzyme stereospecificity?

Accepted Answer

Enzymes selectively catalyze reactions for specific stereoisomers.

Question 11

Which statement about the effect of enzymes on reaction equilibrium is correct?

Accepted Answer

Enzymes do not affect the position of equilibrium; they only affect the rate.

Question 12

Which of the following is an example of an enzyme coupling an unfavorable reaction to a favorable one?

Accepted Answer

Phosphorylation of glucose by hexokinase using ATP.

Question 13

Which of the following terms refers to the region of an enzyme where substrate binding and catalysis occur?

Accepted Answer

Active site

Question 14

Why is preferential binding to the transition state ($$TS) $$important for enzyme catalysis?

Accepted Answer

It lowers the activation energy $$\Delta G$$^{\ddagger}$$, increasing the reaction rate.

Question 15

Which of the following is a correct definition of a coenzyme?

Accepted Answer

A non-protein molecule required for enzyme activity, often derived from vitamins.

Question 16

Which of the following best describes the effect of entropy reduction in enzyme catalysis?

Accepted Answer

It brings substrates into close proximity and correct orientation, facilitating reaction.

Question 17

A genetic disease results from a mutation that reduces the activity of a metabolic enzyme. Which of the following is a likely consequence?

Accepted Answer

Accumulation of substrate and deficiency of product.

Question 18

Which of the following is NOT a function of enzyme catalysis?

Accepted Answer

Increasing the spontaneity ($$\Delta G) of a $$reaction.

Question 19

Which of the following statements about the enzyme-substrate complex ($$ES) is $$correct?

Accepted Answer

It represents a stable intermediate that is always lower in energy than the transition state.

Introduction to Enzymes: Properties, Mechanisms, and Biological Relevance

Study Guide - Practice Questions