Question 1

Which of the following statements best describes how an enzyme increases the rate of a chemical reaction?

Accepted Answer

It lowers the activation energy required to reach the transition state.

Question 2

A researcher is studying the enzyme hexokinase, which can bind either ATP or glucose first. What type of multisubstrate reaction mechanism does hexokinase use?

Accepted Answer

Random substrate binding

Question 3

Which of the following is true regarding the Michaelis–Menten constant $$K_M$$?

Accepted Answer

It indicates the substrate concentration at which the reaction rate is half of $$V_{max}.$$

Question 4

A patient is exposed to diisopropyl fluorophosphate (DFP), which covalently binds to the active site serine of acetylcholinesterase. What type of enzyme inhibition is this?

Accepted Answer

Irreversible inhibition

Question 5

Which of the following best describes the effect of a competitive inhibitor on enzyme kinetics?

Accepted Answer

It increases apparent $$K_M$$ but does not change $$V_{max}.$$

Question 6

Which of the following mechanisms is NOT a way enzymes achieve rate acceleration?

Accepted Answer

Increasing the free energy of the transition state

Question 7

A Lineweaver–Burk plot is used to analyze enzyme kinetics. Which equation represents the Lineweaver–Burk transformation of the Michaelis–Menten equation?

Accepted Answer

$$\frac{1}{v} = \frac{K_M}{V_{max}} \cdot \frac{1}{[S]} + \frac{1}{V_{max}}$$

Question 8

Which of the following statements about allosteric enzymes is correct?

Accepted Answer

They can be regulated by both substrate binding (homoallostery) and nonsubstrate effector molecules (heteroallostery).

Question 9

Which of the following is an example of irreversible covalent modification regulating enzyme activity?

Accepted Answer

Proteolytic activation of zymogens

Question 10

A scientist measures the initial rate of an enzyme-catalyzed reaction at various substrate concentrations and plots $$v$$ versus $$[S]. At $$high $$[S]$$, the rate approaches a maximum. What is this maximum rate called?

Accepted Answer

$$V_{max}$$

Question 11

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

Accepted Answer

The enzyme changes conformation upon substrate binding to better accommodate the substrate.

Question 12

Which of the following is a function of coenzymes or cofactors in enzymatic catalysis?

Accepted Answer

They are required for efficient catalytic activity and are not irreversibly changed during catalysis.

Question 13

A mutation in the gene encoding chymotrypsin results in the loss of the serine residue in the catalytic triad. What is the most likely consequence?

Accepted Answer

The enzyme will lose its ability to hydrolyze peptide bonds efficiently.

Question 14

Which of the following is true about uncompetitive inhibition?

Accepted Answer

Both $$K_M$$ and $$V_{max}$$ are decreased.

Question 15

Which equation represents the Michaelis–Menten equation for a simple enzymatic reaction?

Accepted Answer

$$v = \frac{V_{max} \cdot [S]}{K_M + [S]}$$

Question 16

Which of the following is a property of ribozymes?

Accepted Answer

They are ribonucleic acids that catalyze chemical reactions.

Question 17

A researcher observes that an enzyme's activity is regulated by feedback inhibition at a committed step in a metabolic pathway. What is the most likely effect of this regulation?

Accepted Answer

It helps maintain homeostasis by preventing overproduction of the pathway's end product.

Question 18

Which of the following best describes the effect of temperature on the rate constant $$k of a $$chemical reaction?

Accepted Answer

Increasing temperature increases the rate constant $$k.$$

Question 19

An enzyme catalyzes a reaction with a $$k_{cat} of$$ $$1000\ 	ext{s}^{-1}$$ and a $$K_M of$$ $$10\ \mu	ext{M}. $$What is the enzyme's catalytic efficiency?

Accepted Answer

$$k_{cat} / K_M = 100\ 	ext{s}^{-1}\mu	ext{M}^{-1}$$

Enzymes: Biological Catalysts – Comprehensive Study Notes

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