Question 1

Which of the following best describes an allosteric enzyme?

Accepted Answer

An enzyme whose activity is regulated by binding of effectors at a site other than the active site.

Question 2

According to the Monod-Wyman-Changeux (MWC) model, allosteric proteins can exist in which two states?

Accepted Answer

R (relaxed) and T (tense)

Question 3

Which of the following is a common covalent modification that regulates enzyme activity?

Accepted Answer

Phosphorylation of Ser, Thr, or Tyr residues

Question 4

What is the role of protein phosphatases in enzyme regulation?

Accepted Answer

They remove phosphate groups from proteins.

Question 5

Which molecule acts as a second messenger in the activation of protein kinase A?

Accepted Answer

cAMP

Question 6

Glycogen phosphorylase is regulated by both allosteric effectors and covalent modification. Which of the following statements is TRUE regarding its regulation?

Accepted Answer

AMP activates glycogen phosphorylase allosterically.

Question 7

Which of the following best explains the Bohr effect in hemoglobin?

Accepted Answer

Decreased pH promotes oxygen release from hemoglobin.

Question 8

What is the physiological significance of the sigmoid oxygen-binding curve of hemoglobin?

Accepted Answer

It enables efficient oxygen loading in the lungs and unloading in the tissues.

Question 9

Which of the following is a consequence of acetylation of lysine residues in metabolic enzymes?

Accepted Answer

It can either activate or inhibit the enzyme, depending on the context.

Question 10

Which of the following statements about isozymes is correct?

Accepted Answer

Isozymes are enzymes with slightly different subunits that catalyze the same reaction.

Question 11

A patient with sickle-cell anemia has a mutation in the hemoglobin β-chain. What is the molecular basis of this disease?

Accepted Answer

A glutamate is replaced by valine at position 6 of the β-chain.

Question 12

Which equation describes the oxygen binding to hemoglobin assuming cooperative binding?

Accepted Answer

$$Y = \frac{pO_2$^n}{pO_2$^n + K^n}$$

Question 13

Which of the following is a feed-forward activator in a metabolic pathway?

Accepted Answer

A molecule produced early in the pathway that activates an enzyme downstream.

Question 14

Which of the following statements about the KNF sequential model for allosteric regulation is TRUE?

Accepted Answer

Ligand binding induces conformational changes that can affect adjacent subunits.

Question 15

Which of the following is NOT a factor that influences enzymatic activity?

Accepted Answer

Enzyme denaturation by boiling

Question 16

Which of the following best describes the role of 2,3-bisphosphoglycerate (2,3-BPG) in hemoglobin function?

Accepted Answer

It decreases hemoglobin's affinity for oxygen, promoting oxygen release in tissues.

Question 17

Which of the following is TRUE regarding the quaternary structure of hemoglobin?

Accepted Answer

Hemoglobin is a tetramer composed of two α and two β chains.

Question 18

Which of the following is a direct result of the phosphorylation of glycogen phosphorylase?

Accepted Answer

It converts the enzyme from a less-active to a more-active form.

Question 19

Which of the following is a property of regulatory enzymes?

Accepted Answer

They are often situated at key steps in metabolic pathways.

Question 20

Which of the following is TRUE about the relationship between myoglobin and hemoglobin?

Accepted Answer

Myoglobin is monomeric, while hemoglobin is tetrameric.

Enzyme Regulation: Mechanisms and Physiological Significance

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