Question 1

Which of the following best describes the role of an allosteric effector in enzyme regulation?

Accepted Answer

It modifies the enzyme's activity by altering the conformation(s) of its quaternary structure.

Question 2

Aspartate transcarbamoylase (ATCase) is regulated by feedback inhibition. Which molecule acts as an allosteric inhibitor of ATCase?

Accepted Answer

CTP

Question 3

In the concerted (Monod-Wyman-Changeux) model of allosteric enzymes, which statement is correct?

Accepted Answer

All subunits change conformation simultaneously from T to R state.

Question 4

Which of the following equations correctly represents the ratio of dissociation constants in the Monod-Wyman-Changeux model?

Accepted Answer

$$c = \frac{K_R}{K_T}$$

Question 5

What is the effect of an allosteric activator on the equilibrium between the T and R states of an enzyme?

Accepted Answer

It stabilizes the R (active) state.

Question 6

Which of the following best describes homotropic effects in allosteric enzymes?

Accepted Answer

Interactions when several identical molecules bind to the protein.

Question 7

In the sequential model of allosteric enzyme behavior, what is the primary mechanism of cooperativity?

Accepted Answer

Substrate binding induces conformational changes in individual subunits, increasing affinity for additional substrate.

Question 8

Which of the following is true regarding the organization of ATCase?

Accepted Answer

It consists of 6 catalytic subunits organized into 2 trimers and 6 regulatory subunits organized into 3 dimers.

Question 9

Which of the following statements about feedback inhibition is correct?

Accepted Answer

The final product of a pathway inhibits the first enzyme in the pathway.

Question 10

Which of the following best explains the sigmoidal shape of the velocity vs. substrate concentration curve for ATCase?

Accepted Answer

It reflects cooperative binding of substrate to multiple subunits.

Question 11

Which parameter is altered by an allosteric inhibitor in a K system?

Accepted Answer

$$K_{0.5}$$

Question 12

Which amino acid side chains are commonly phosphorylated to regulate enzyme activity?

Accepted Answer

Serine, threonine, and tyrosine

Question 13

What is the role of phosphorylation in enzyme regulation?

Accepted Answer

It can convert an inactive precursor into an active enzyme.

Question 14

Which of the following statements about zymogens is correct?

Accepted Answer

They are inactive precursors that require proteolytic cleavage for activation.

Question 15

Chymotrypsinogen is converted to active chymotrypsin by which process?

Accepted Answer

Proteolytic cleavage by trypsin

Question 16

Which of the following best describes the role of NAD$$^+ in $$biochemical reactions?

Accepted Answer

It acts as a two-electron oxidizing agent and is reduced to NADH.

Question 17

Which coenzyme is involved in the transfer of amino groups during transamination reactions?

Accepted Answer

Pyridoxal phosphate

Question 18

Which of the following is a feature of the active site of chymotrypsin?

Accepted Answer

It contains critical amino acids in close proximity that facilitate catalysis.

Question 19

Which statement best describes the mechanism of action of critical amino acids in chymotrypsin?

Accepted Answer

The oxygen atom acts as a nucleophile attacking the carbonyl group of the peptide bond.

Question 20

Which of the following is true about coenzymes?

Accepted Answer

They are nonprotein substances that participate in enzymatic reactions and are regenerated for further reaction.

Allosteric Enzymes and Regulation: Structure, Mechanisms, and Models Ch 7

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