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

A decrease in pH (increase in H\textsuperscript{+}) and increase in pCO\textsubscript{2} decrease hemoglobin's oxygen affinity, shifting the oxygen-dissociation curve to the right.

Q: Which of the following equations correctly represents the conversion of carbon dioxide to bicarbonate in red blood cells?

$\mathrm{CO_2} + \mathrm{H_2O} \xrightarrow{\text{carbonic anhydrase}} \mathrm{H_2CO_3} \rightarrow \mathrm{HCO_3^-} + \mathrm{H^+}$

Question 1

Which statement best explains why myoglobin has a hyperbolic oxygen-dissociation curve while hemoglobin has a sigmoidal curve?

Accepted Answer

Myoglobin binds a single oxygen molecule without cooperativity, resulting in a hyperbolic curve, whereas hemoglobin's four subunits exhibit cooperative binding, producing a sigmoidal curve.

Question 2

What is the primary effect of 2,3-bisphosphoglycerate (2,3-BPG) on hemoglobin's oxygen affinity?

Accepted Answer

2,3-BPG decreases hemoglobin's affinity for oxygen by stabilizing the T (taut) form, shifting the oxygen-dissociation curve to the right.

Question 3

A patient receives a transfusion of stored blood that is depleted of 2,3-BPG. What is the most likely consequence for oxygen delivery to tissues?

Accepted Answer

Oxygen delivery to tissues will be impaired because hemoglobin will hold onto oxygen more tightly.

Question 4

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

Accepted Answer

A decrease in pH (increase in H	extsuperscript{+}) and increase in pCO	extsubscript{2} decrease hemoglobin's oxygen affinity, shifting the oxygen-dissociation curve to the right.

Question 5

Which amino acid substitution is responsible for sickle cell anemia (HbS)?

Accepted Answer

Glutamate is replaced by valine at position 6 of the beta chain.

Question 6

Why does fetal hemoglobin (HbF) have a higher oxygen affinity than adult hemoglobin (HbA)?

Accepted Answer

HbF binds 2,3-BPG less tightly than HbA, resulting in higher oxygen affinity.

Question 7

A patient with chronic hypoxia is found to have elevated levels of 2,3-BPG in their red blood cells. What is the physiological significance of this adaptation?

Accepted Answer

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

Question 8

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

Accepted Answer

$\mathrm{CO_2} + \mathrm{H_2O} \xrightarrow{	ext{carbonic anhydrase}} \mathrm{H_2CO_3} ightarrow \mathrm{HCO_3^-} + \mathrm{H^+}$

Question 9

Which structural feature allows hemoglobin to exhibit cooperative binding of oxygen?

Accepted Answer

Its tetrameric structure composed of two alpha and two beta chains, allowing conformational changes between T and R states.

Question 10

What is the effect of carbon monoxide (CO) binding to hemoglobin?

Accepted Answer

It forms carboxyhemoglobin, shifting the oxygen-dissociation curve to the left and reducing oxygen delivery.

Question 11

Which of the following best describes the role of the proximal histidine (F8) in myoglobin?

Accepted Answer

It stabilizes the heme group by binding to the iron atom.

Question 12

A patient with beta-thalassemia major is likely to present with which of the following clinical features?

Accepted Answer

Severe anemia due to decreased production of beta-globin chains, requiring regular blood transfusions.

Question 13

Which of the following is a consequence of the sickling of red blood cells in sickle cell anemia?

Accepted Answer

Blockage of capillaries, leading to localized tissue ischemia and pain.

Question 14

Which form of hemoglobin is favored at low oxygen partial pressures and is stabilized by 2,3-BPG?

Accepted Answer

T (taut) form

Question 15

Which equation best represents the Bohr effect in hemoglobin?

Accepted Answer

$\mathrm{HbO_2} + \mathrm{H^+} \rightarrow \mathrm{HbH} + \mathrm{O_2}$

Question 16

Which of the following is true regarding the oxygen affinity of myoglobin compared to hemoglobin at low pO	extsubscript{2}?

Accepted Answer

Myoglobin has a higher oxygen affinity than hemoglobin at low pO	extsubscript{2}.

Question 17

Which of the following best explains the selective advantage of sickle cell trait in regions where malaria is endemic?

Accepted Answer

Individuals with sickle cell trait have increased resistance to malaria because their red blood cells have a shorter lifespan, preventing completion of the parasite's life cycle.

Question 18

Which of the following statements about the structure of the heme group is correct?

Accepted Answer

The iron atom (Fe	extsuperscript{2+}) is coordinated to four nitrogen atoms of the porphyrin ring and can form two additional bonds perpendicular to the plane.

Question 19

Which of the following is a direct consequence of increased 2,3-BPG levels in red blood cells during chronic anemia?

Accepted Answer

Hemoglobin's oxygen affinity decreases, facilitating oxygen release to tissues.

Structure and Function of Globular Hemeproteins: Myoglobin and Hemoglobin

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