Question 1

Which of the following best describes the role of enzymes in cellular reactions with respect to activation energy ($$E_A) $$and free energy change ($$\Delta G$$)?

Accepted Answer

Enzymes decrease $$E_A$$ but do not change $$\Delta G.$$

Question 2

A scientist is studying an enzyme-catalyzed reaction and observes that increasing substrate concentration no longer increases the reaction rate. Which concept best explains this observation?

Accepted Answer

The enzyme is saturated and has reached $$V_{max}.$$

Question 3

Which of the following statements about enzyme specificity is correct?

Accepted Answer

Enzyme specificity is determined by the shape and chemical properties of the active site.

Question 4

A patient is given a drug that binds irreversibly to the active site of an enzyme. What is the most likely effect on enzyme activity?

Accepted Answer

The enzyme activity will be permanently inhibited.

Question 5

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

Accepted Answer

Transferases

Question 6

An enzyme has a $$K_M of 5 mM $$for its substrate. What does this value indicate about the enzyme's affinity for the substrate?

Accepted Answer

The enzyme has low affinity for the substrate.

Question 7

Which of the following is a property shared by most enzymes?

Accepted Answer

They increase reaction rates by decreasing $$E_A.$$

Question 8

A competitive inhibitor affects an enzyme-catalyzed reaction by:

Accepted Answer

Binding to the active site and increasing $$K_M.$$

Question 9

Which scenario best illustrates allosteric regulation of an enzyme?

Accepted Answer

A molecule binds to a site other than the active site, changing enzyme activity.

Question 10

If an enzyme is regulated by phosphorylation, which type of regulation is this?

Accepted Answer

Chemical modification

Question 11

Which of the following best describes the 'metastable state' in cellular reactions?

Accepted Answer

A state where reactants are thermodynamically favorable but kinetically hindered.

Question 12

Which enzyme class is responsible for catalyzing the rearrangement of atoms within a molecule?

Accepted Answer

Isomerases

Question 13

A cell needs to rapidly decrease the activity of a specific enzyme. Which mechanism would be most effective for immediate regulation?

Accepted Answer

Allosteric inhibition by a regulatory molecule.

Question 14

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

Accepted Answer

$$k_{cat} is $$the number of substrate molecules converted to product per enzyme molecule per second.

Question 15

Which property distinguishes noncompetitive inhibitors from competitive inhibitors?

Accepted Answer

Noncompetitive inhibitors decrease $$V_{max}$$, while competitive inhibitors do not.

Question 16

A hydrolase enzyme is most likely to catalyze which type of reaction?

Accepted Answer

Cleavage of bonds by addition of water

Question 17

Which of the following factors can affect enzyme activity by altering protein structure?

Accepted Answer

pH, temperature, and ion concentration

Question 18

A researcher finds that an enzyme's activity is regulated by sequestration. What does this mean?

Accepted Answer

The enzyme is stored in a cellular compartment away from substrates.

Question 19

Which of the following best explains why enzyme-catalyzed reactions proceed at 'useful rates' in cells?

Accepted Answer

Enzymes decrease $$E_A$$, allowing reactions to reach equilibrium quickly.

Question 20

A mutation causes an enzyme's active site to change shape. Which outcome is most likely?

Accepted Answer

The enzyme's specificity for its substrate will decrease.

Enzymes: The Catalysts of Life (Chapter 6 Review)

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