Question 1

Which of the following statements best describes the main assumption of the Monod-Wyman-Changeux (MWC) model of allosteric regulation?

Accepted Answer

All subunits of the protein must be in the same conformation (either all R or all T) at any given time.

Question 2

In the MWC model, what is the effect of an allosteric activator on the equilibrium between the T and R states?

Accepted Answer

It shifts the equilibrium toward the R state, decreasing $$L = \frac{T_0$}{R_0$}.$$

Question 3

Which of the following best explains why hemoglobin exhibits a sigmoidal oxygen binding curve while myoglobin does not?

Accepted Answer

Hemoglobin displays cooperative binding due to its quaternary structure, while myoglobin is monomeric and does not.

Question 4

A substrate that enhances its own binding to an enzyme by inducing a conformational change is called a:

Accepted Answer

homotropic modulator

Question 5

Which of the following is a limitation of the MWC model?

Accepted Answer

It does not account for negative cooperativity in substrate binding.

Question 6

In the context of hemoglobin, what is the Bohr effect?

Accepted Answer

The decrease in oxygen affinity with increasing proton concentration.

Question 7

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

Accepted Answer

BPG binds between the beta subunits and stabilizes the T state, promoting oxygen release.

Question 8

Which of the following equations correctly represents the equilibrium constant $$L in $$the MWC model?

Accepted Answer

$$L = \frac{T_0$}{R_0$}$$

Question 9

A patient with a mutation that decreases the ability of hemoglobin to bind BPG would most likely experience which of the following?

Accepted Answer

Decreased oxygen release in tissues.

Question 10

Which of the following statements about the KNF (sequential) model is correct?

Accepted Answer

Ligand binding to one subunit induces a conformational change in that subunit, which can be transmitted to neighboring subunits.

Question 11

Which of the following best describes a K system in allosteric regulation?

Accepted Answer

Allosteric effectors change $$K_{0.5}$$ but $$V_{max}$$ remains the same.

Question 12

Which of the following is a direct effect of carbon dioxide binding to hemoglobin?

Accepted Answer

It forms a carbamate group, stabilizing the T state and promoting oxygen release.

Question 13

Which of the following best explains why myoglobin is more effective than hemoglobin at storing oxygen in muscle tissue?

Accepted Answer

Myoglobin has a higher affinity for oxygen at all partial pressures.

Question 14

Which of the following amino acid residues is directly involved in the Bohr effect in hemoglobin?

Accepted Answer

His146 in the beta subunit

Question 15

A mutation in hemoglobin that prevents the formation of salt bridges in the T state would most likely result in:

Accepted Answer

Decreased stability of the T state and increased oxygen affinity.

Question 16

Which of the following best describes the effect of a negative heterotropic effector on an allosteric enzyme?

Accepted Answer

It decreases the enzyme's affinity for substrate.

Question 17

Which of the following best explains why the oxygen binding curve of hemoglobin is sigmoidal?

Accepted Answer

The binding of one oxygen molecule increases the affinity of the remaining subunits for oxygen.

Question 18

Which of the following statements about allosteric enzymes is correct?

Accepted Answer

Their activity can be changed by changes in intersubunit interactions.

Question 19

Which of the following best describes the effect of pH on oxygen binding to hemoglobin?

Accepted Answer

Lower pH decreases hemoglobin's affinity for oxygen.

LEC 15 Allosteric Regulation and Oxygen-Binding Proteins: Mechanisms and Models

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