Question 1

Which class of macromolecules do most enzymes belong to?

Accepted Answer

Polypeptides

Question 2

The hydrolysis of ATP is thermodynamically favorable, yet ATP remains stable in water for days. What explains this phenomenon?

Accepted Answer

The activation energy barrier prevents the reaction from occurring rapidly

Question 3

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

Accepted Answer

They lower the activation energy required for reactions

Question 4

A reaction has a high activation energy ($$E_a) $$and is thermodynamically favorable. What is the most likely state of the reactants in a cell?

Accepted Answer

Metastable state

Question 5

Which of the following is NOT a property of enzymes as biological catalysts?

Accepted Answer

They permanently alter the position of equilibrium

Question 6

Which amino acids are most commonly found in the active site of enzymes due to their ability to participate in catalysis?

Accepted Answer

Cysteine, histidine, serine, aspartate, glutamate, lysine

Question 7

Which model best explains the specificity and flexibility of enzyme-substrate interactions?

Accepted Answer

Induced-fit model

Question 8

A competitive inhibitor affects enzyme activity by:

Accepted Answer

Binding to the active site and preventing substrate binding

Question 9

Which equation describes the initial velocity ($$v) of an $$enzyme-catalyzed reaction according to Michaelis-Menten kinetics?

Accepted Answer

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

Question 10

If the substrate concentration $$[S] is $$much greater than $$K_m$$, what is the approximate value of $$v in $$the Michaelis-Menten equation?

Accepted Answer

$$v \approx V_{max}$$

Question 11

Which plot is used to linearize enzyme kinetic data and determine $$K_m$$ and $$V_{max}$$?

Accepted Answer

Lineweaver-Burk plot

Question 12

A noncompetitive inhibitor affects enzyme activity by:

Accepted Answer

Binding to a site other than the active site and altering enzyme conformation

Question 13

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

Accepted Answer

The end product of a pathway inhibits an enzyme that catalyzes an early step

Question 14

Which of the following statements about enzyme specificity is TRUE?

Accepted Answer

Enzymes are highly specific due to the shape and chemistry of their active site

Question 15

Which of the following is a ribozyme?

Accepted Answer

Ribonuclease P

Question 16

Which of the following is a major class of enzymes responsible for transferring phosphate groups?

Accepted Answer

Transferases

Question 17

What is the effect of increasing temperature on enzyme activity in human cells beyond the optimal temperature?

Accepted Answer

Enzyme activity decreases due to denaturation

Question 18

Which mechanism allows enzymes to be regulated by the addition or removal of phosphate groups?

Accepted Answer

Covalent modification

Question 19

Which of the following best describes the effect of a catalyst on the activation energy ($$E_a) of a $$reaction?

Accepted Answer

It decreases $$E_a$$

Question 20

A patient is exposed to cyanide, which inhibits cytochrome c oxidase. What is the most immediate cellular consequence?

Accepted Answer

Blocked ATP synthesis due to inhibition of electron transport

Enzymes: The Catalysts of Life – Structure, Function, and Regulation

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