Question 1

Which of the following best describes the role of myoglobin (Mb) in oxygen physiology?

Accepted Answer

Mb stores O$$_2 in $$muscle cells for rapid release during intense activity.

Question 2

Which statement correctly defines a prosthetic group in the context of hemoglobin (Hb) and myoglobin (Mb)?

Accepted Answer

A prosthetic group is a non-protein molecule tightly bound to a protein, essential for its function.

Question 3

Which of the following best describes the general structure of heme?

Accepted Answer

Heme is a planar porphyrin ring with a central Fe$$^{2+}$$ ion.

Question 4

How many coordination sites does the Fe$$^{2+}$$ ion in heme possess, and which site is used for O$$_2$$ binding?

Accepted Answer

Fe$$^{2+}$$ has 6 coordination sites; O$$_2$$ binds to the sixth site.

Question 5

Which equation correctly defines fractional saturation ($$Y) $$for myoglobin?

Accepted Answer

$$Y = \frac{[$$MbO_2$$]}{[Mb] + [$$MbO_2$$]}$$

Question 6

What is the role of the distal histidine (His) in the heme pocket of myoglobin and hemoglobin?

Accepted Answer

It stabilizes bound O$$_2$$ through hydrogen bonding and reduces CO binding affinity.

Question 7

During the T to R transition in hemoglobin upon O$$_2$$ binding, which of the following occurs?

Accepted Answer

The Fe$$^{2+}$$ ion moves into the plane of the heme, triggering a shift in the quaternary structure.

Question 8

Which of the following best describes cooperative binding in hemoglobin?

Accepted Answer

Binding of O$$_2 to $$one subunit increases the affinity of other subunits for O$$_2.$$

Question 9

Which model describes hemoglobin as existing in either a T (tense) or R (relaxed) state, with all subunits switching simultaneously?

Accepted Answer

MWC (concerted) model

Question 10

Which of the following is an allosteric effector of hemoglobin that decreases its affinity for O$$_2$$?

Accepted Answer

2,3-bisphosphoglycerate (2,3-BPG)

Question 11

Which amino acids are primarily involved in binding 2,3-BPG in hemoglobin?

Accepted Answer

Positively charged amino acids (e.g., lysine and histidine) in the central cavity

Question 12

If a mutation replaces a positively charged amino acid in the 2,3-BPG binding pocket of hemoglobin with a neutral amino acid, what is the most likely effect on O$$_2$$ binding?

Accepted Answer

Hemoglobin's affinity for O$$_2$$ will increase.

Question 13

Which of the following best explains why fetal hemoglobin (HbF) has a higher affinity for O$$_2$$ than maternal hemoglobin (HbA)?

Accepted Answer

HbF has fewer positively charged amino acids in the 2,3-BPG binding pocket, reducing 2,3-BPG binding.

Question 14

Which equation best represents the Bohr effect, showing the relationship between O$$_2$$ binding and pH?

Accepted Answer

$$Hb + O_2$ ightleftharpoons $$HbO_2$$; 	ext{O}_2 	ext{ affinity decreases as } [H^+] 	ext{ increases}$$

Question 15

A patient with chronic respiratory acidosis has elevated CO$$_2$$ and H$$^+$$ levels. What effect does this have on hemoglobin's O$$_2$$ binding curve?

Accepted Answer

The O$$_2$$ binding curve shifts to the right, decreasing O$$_2$$ affinity.

Question 16

Which of the following best describes the O$$_2$$ binding curve for myoglobin compared to hemoglobin?

Accepted Answer

Myoglobin's curve is hyperbolic, while hemoglobin's is sigmoidal.

Question 17

Which scenario would most likely result in a rightward shift of the hemoglobin O$$_2$$ binding curve?

Accepted Answer

Increased CO$$_2$$ concentration

Question 18

Which of the following statements about allosteric regulation is correct?

Accepted Answer

Allosteric regulation involves binding of effectors at sites other than the active site, altering protein function.

Question 19

A hemoglobin variant has a mutation that increases its affinity for 2,3-BPG. What is the most likely effect on O$$_2$$ delivery to tissues?

Accepted Answer

O$$_2$$ delivery to tissues will decrease due to reduced O$$_2$$ affinity.

Protein Function: Myoglobin and Hemoglobin – Structure, Oxygen Binding, and Regulation

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