Question 1

Why is carbon monoxide (CO) toxic to aerobic organisms?

Accepted Answer

CO binds to hemoglobin with much higher affinity than oxygen, preventing oxygen transport to tissues.

Question 2

For the binding of a ligand to a protein, what is the relationship between the $$K_a ($$association constant), the $$K_d ($$dissociation constant), and the affinity of the protein for the ligand?

Accepted Answer

A high $$K_a$$ and a low $$K_d$$ both indicate high affinity of the protein for the ligand.

Question 3

Explain briefly why the relative affinity of heme for oxygen and carbon monoxide is changed by the presence of the myoglobin protein.

Accepted Answer

The protein environment of myoglobin reduces the affinity of heme for CO relative to free heme, due to steric hindrance and specific interactions that favor O$$_2$$ binding.

Question 4

Which of the following best describes the function of myoglobin in muscle tissue?

Accepted Answer

It serves as an oxygen-storage protein, releasing oxygen when muscle oxygen levels are low.

Question 5

The binding of oxygen to the single binding site of myoglobin results in a hyperbolic binding curve. What does this indicate about the nature of oxygen binding to myoglobin?

Accepted Answer

There is no cooperativity in oxygen binding to myoglobin.

Question 6

Describe briefly the two principal models for the cooperative binding of ligands to proteins such as hemoglobin.

Accepted Answer

The concerted model (all subunits switch together) and the sequential model (subunits change conformation one at a time).

Question 7

How does 2,3-bisphosphoglycerate (BPG) binding to hemoglobin decrease its affinity for oxygen?

Accepted Answer

BPG binds to a cavity between the beta subunits, stabilizing the low-affinity T state.

Question 8

What is the effect of pH on the binding of oxygen to hemoglobin (the Bohr Effect)?

Accepted Answer

A decrease in pH (more acidic) decreases hemoglobin's affinity for oxygen.

Question 9

Which of the following equations correctly represents the Bohr Effect in hemoglobin?

Accepted Answer

$$\mathrm{HbO}_2 + H^+ \rightleftharpoons \mathrm{HbH}^+ + \mathrm{O}_2$$

Question 10

A patient with sickle cell disease has a mutation in the beta chain of hemoglobin. Which amino acid substitution is responsible for this disease, and what is its effect?

Accepted Answer

Glutamate is replaced by valine at position 6, causing hemoglobin to polymerize under low oxygen conditions.

Question 11

Which of the following best explains why fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin?

Accepted Answer

Fetal hemoglobin binds BPG less strongly, resulting in a higher oxygen affinity.

Question 12

A mountain climber at high altitude experiences increased levels of BPG in the blood. What is the physiological significance of this adaptation?

Accepted Answer

Increased BPG decreases hemoglobin's affinity for oxygen, facilitating oxygen release to tissues.

Question 13

Which of the following statements about the oxygen-binding curve of hemoglobin is correct?

Accepted Answer

It is sigmoidal, reflecting cooperative binding of oxygen.

Question 14

If a mutation in hemoglobin increases its affinity for oxygen, what is the likely effect on oxygen delivery to tissues?

Accepted Answer

Oxygen delivery to tissues will decrease because hemoglobin will not release oxygen as readily.

Question 15

Which of the following best describes the effect of CO binding to hemoglobin in the presence of oxygen?

Accepted Answer

CO binding increases the affinity of the remaining sites for oxygen, but prevents oxygen release to tissues.

Question 16

A patient is exposed to high levels of CO. Which treatment is most effective for restoring oxygen transport?

Accepted Answer

Administering 100% oxygen to outcompete CO for hemoglobin binding.

Question 17

Which of the following equations represents the equilibrium constant for ligand binding to a protein?

Accepted Answer

$$K_a = \frac{[PL]}{[P][L]}$$

Question 18

Which of the following best explains the molecular basis for the Bohr Effect?

Accepted Answer

Protonation of certain amino acid residues stabilizes the T state of hemoglobin, reducing oxygen affinity at low pH.

Hemoglobin and Myoglobin: Structure, Function, and Oxygen Binding

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