Question 1

Which of the following best explains why hemoglobin displays a sigmoidal oxygen dissociation curve, while myoglobin displays a hyperbolic curve?

Accepted Answer

Hemoglobin is an allosteric protein with multiple subunits that exhibit cooperative binding, whereas myoglobin is a monomer and binds oxygen independently.

Question 2

A patient with a mutation in the β chain of hemoglobin that replaces glutamate with valine is most likely to develop which of the following conditions?

Accepted Answer

Sickle cell disease

Question 3

Which of the following statements about 2,3-bisphosphoglycerate (2,3-BPG) is correct?

Accepted Answer

2,3-BPG binds to the T state of hemoglobin, stabilizing it and promoting oxygen release.

Question 4

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

Accepted Answer

The Bohr effect is the decreased affinity of hemoglobin for oxygen in the presence of high concentrations of hydrogen ions and carbon dioxide.

Question 5

A researcher creates a mutant hemoglobin with an oxygen dissociation curve that is shifted far to the left compared to normal hemoglobin. What is the most likely physiological consequence of this mutation?

Accepted Answer

The mutant hemoglobin will bind oxygen tightly in the lungs but will not efficiently release it at the tissues.

Question 6

Which of the following is true regarding the structural changes in hemoglobin upon oxygen binding?

Accepted Answer

Oxygen binding causes the two αβ dimers to rotate by approximately 15 degrees relative to each other, shifting hemoglobin from the T state to the R state.

Question 7

Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA). What is the molecular basis for this difference?

Accepted Answer

HbF has a γ chain instead of a β chain, resulting in weaker binding to 2,3-BPG.

Question 8

Which of the following equations correctly represents the conversion of carbon dioxide to carbonic acid in red blood cells?

Accepted Answer

$$\mathrm{CO_2$ + H_2O \rightarrow H_2CO_3}$$

Question 9

A patient is exposed to carbon monoxide (CO). Which of the following best explains why CO is so dangerous in terms of hemoglobin function?

Accepted Answer

CO binds to the heme iron at the same site as oxygen, but with much higher affinity, preventing oxygen transport.

Question 10

Which of the following best describes the role of the proximal histidine in myoglobin and hemoglobin?

Accepted Answer

It coordinates directly to the iron atom in the heme group, stabilizing its position.

Question 11

Which of the following statements about neuroglobin is correct?

Accepted Answer

Neuroglobin is a monomeric protein expressed in the brain and retina, and may protect neural tissues from hypoxia.

Question 12

A patient with thalassemia is found to have hemoglobin tetramers containing only α chains. What is the most likely consequence of this abnormality?

Accepted Answer

The hemoglobin will be unstable and unable to efficiently transport oxygen.

Question 13

Which of the following best explains why the iron atom in heme moves into the plane of the porphyrin ring upon oxygen binding?

Accepted Answer

Partial electron transfer from the iron to the oxygen atom reduces the ionic radius of iron, allowing it to fit into the plane.

Question 14

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

Accepted Answer

CO$$_2$$ binds to the amino termini of hemoglobin chains, forming carbamates that stabilize the T state.

Question 15

Which of the following best describes the difference in oxygen binding between myoglobin and hemoglobin at the partial pressure of oxygen found in tissues?

Accepted Answer

Hemoglobin releases a significant portion of its bound oxygen, while myoglobin remains highly saturated.

Question 16

A new therapy for carbon monoxide poisoning involves a modified neuroglobin that binds CO 500 times more tightly than hemoglobin. What is the most likely mechanism by which this therapy works?

Accepted Answer

The modified neuroglobin binds CO, removing it from hemoglobin and allowing hemoglobin to resume oxygen transport.

Question 17

Which of the following best describes the effect of a rightward shift in the hemoglobin oxygen dissociation curve?

Accepted Answer

Hemoglobin has a lower affinity for oxygen and releases more oxygen at the tissues.

Question 18

Which of the following is a feature shared by both neuroglobin and cytoglobin, as described in the study materials?

Accepted Answer

Both are monomeric proteins with proximal and distal histidines coordinated to the iron atom in the deoxy form.

Question 19

A patient with a mutation that prevents 2,3-BPG from binding to hemoglobin would most likely exhibit which of the following symptoms?

Accepted Answer

Impaired oxygen release at the tissues, leading to tissue hypoxia.

Biochemistry: A Short Course 9

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