Question 1

Which of the following best explains why most cellular reactions require enzymes to proceed at appreciable rates?

Accepted Answer

The activation energy ($$E_A) $$barrier is too high for most reactants to overcome at normal cellular temperatures.

Question 2

Which of the following statements about enzyme active sites is CORRECT?

Accepted Answer

The active site is formed by the three-dimensional folding of the protein and binds substrates with high specificity.

Question 3

Which of the following is a property shared by all catalysts, including enzymes?

Accepted Answer

They increase the rate of reaction by lowering the activation energy ($$E_A) $$required.

Question 4

A competitive inhibitor of an enzyme acts by:

Accepted Answer

Binding to the active site and preventing substrate binding.

Question 5

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

Accepted Answer

The enzyme changes shape to fit the substrate upon binding, optimizing catalysis.

Question 6

Which of the following is NOT a mechanism by which enzymes activate substrates?

Accepted Answer

Increasing the temperature of the substrate.

Question 7

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

Accepted Answer

Transferase

Question 8

A patient is exposed to a nerve gas that irreversibly inhibits acetylcholinesterase. What is the most likely molecular mechanism?

Accepted Answer

The inhibitor forms a covalent bond with the enzyme, causing permanent loss of catalytic activity.

Question 9

Which of the following statements about enzyme kinetics is TRUE?

Accepted Answer

At substrate concentration $$[S] = K_m$$, the initial velocity $$v is $$half of $$V_{max}.$$

Question 10

Which of the following is a function of enzyme cofactors?

Accepted Answer

They act as electron acceptors and are indispensable for enzyme activity.

Question 11

Which of the following best describes feedback inhibition in metabolic pathways?

Accepted Answer

The final product of a pathway inhibits an earlier step, regulating the pathway's activity.

Question 12

Which of the following is TRUE regarding ribozymes?

Accepted Answer

They are RNA molecules with catalytic activity.

Question 13

Which of the following modifications is most likely to regulate enzyme activity by reversible addition or removal of a phosphate group?

Accepted Answer

Phosphorylation and dephosphorylation

Question 14

A Lineweaver–Burk plot is used to analyze enzyme kinetics. What is plotted on the y-axis and x-axis, respectively?

Accepted Answer

$$1/v$$ \, vs. \, 1/[S]$

Question 15

Which of the following scenarios would most likely result in enzyme denaturation?

Accepted Answer

Exposing the enzyme to a temperature above its optimal range.

Question 16

Which of the following is an example of an enzyme regulated by proteolytic cleavage?

Accepted Answer

Digestive enzymes of the pancreas, which are activated from zymogens.

Question 17

Which of the following statements about allosteric regulation is CORRECT?

Accepted Answer

Allosteric effectors bind to a site other than the active site and alter enzyme activity.

Question 18

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

Accepted Answer

It decreases $$V_{max}$$ without affecting $$K_m.$$

Question 19

Which of the following is TRUE about the turnover number ($$k_{cat}) of an $$enzyme?

Accepted Answer

It is the number of substrate molecules converted to product per enzyme molecule per unit time at $$V_{max}.$$

CH 6 - Enzymes: The Catalysts of Life – Comprehensive Study Notes

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