$$\text{HHb} + \text{O}_2 \rightleftharpoons \text{HbO}_2 + \text{H}^+$$

Question 1

Which of the following best describes the role of the heme group in myoglobin and hemoglobin?

Accepted Answer

It is a prosthetic group that provides a site for reversible oxygen binding via its central Fe$$^{2+}$$ ion.

Question 2

The porphyrin ring in the heme group contains four nitrogen atoms. What is their primary function?

Accepted Answer

To coordinate the central Fe$$^{2+}$$ ion and prevent its oxidation to Fe$$^{3+}.$$

Question 3

Which equation correctly represents the equilibrium for reversible protein-ligand binding?

Accepted Answer

$$P + L \rightleftharpoons PL$$

Question 4

Given the equation for the fraction of occupied binding sites ($$	heta$$): $$	heta = \frac{[PL]}{[PL] + [P]}$$, what does $$	heta = 0.5$$ indicate?

Accepted Answer

Half of the available binding sites are occupied.

Question 5

Which of the following statements about the oxygen-binding curves of myoglobin and hemoglobin is correct?

Accepted Answer

Myoglobin displays a hyperbolic curve, while hemoglobin displays a sigmoidal curve due to cooperative binding.

Question 6

What is the physiological significance of the sigmoidal oxygen-binding curve of hemoglobin?

Accepted Answer

It allows hemoglobin to bind oxygen efficiently in the lungs and release it efficiently in the tissues.

Question 7

Which of the following best explains why carbon monoxide (CO) is toxic to humans?

Accepted Answer

CO binds to the heme iron in hemoglobin with much higher affinity than O$$_2$$, preventing oxygen transport.

Question 8

The Bohr effect describes the influence of which factors on hemoglobin's affinity for oxygen?

Accepted Answer

pH and CO$$_2$$ concentration

Question 9

Which of the following equations represents the Bohr effect in hemoglobin?

Accepted Answer

$$	ext{HHb} + 	ext{O}_2 ightleftharpoons 	ext{HbO}_2 + 	ext{H}^+$$

Question 10

What is the effect of 2,3-bisphosphoglycerate (BPG) on hemoglobin?

Accepted Answer

It decreases hemoglobin's affinity for oxygen, facilitating oxygen release in tissues.

Question 11

A patient with sickle cell anemia has a mutation in the β chain of hemoglobin. What is the molecular consequence of this mutation?

Accepted Answer

A hydrophobic valine replaces a hydrophilic glutamate, causing hemoglobin to aggregate when deoxygenated.

Question 12

Which of the following best describes allosteric regulation in hemoglobin?

Accepted Answer

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

Question 13

Which of the following statements about fetal hemoglobin is correct?

Accepted Answer

Fetal hemoglobin has a lower affinity for BPG, resulting in higher oxygen affinity compared to adult hemoglobin.

Question 14

Which of the following is true regarding the T (tense) and R (relaxed) states of hemoglobin?

Accepted Answer

The R state is stabilized by oxygen binding and has a higher affinity for oxygen.

Question 15

Which of the following best explains why myoglobin is not suitable for oxygen transport in blood?

Accepted Answer

Myoglobin binds oxygen with high affinity and does not release it efficiently at tissue oxygen concentrations.

Question 16

Which of the following is a homotropic allosteric modulator of hemoglobin?

Accepted Answer

O$$_2$$

Question 17

What is the effect of decreasing blood pH from 7.6 to 7.2 on hemoglobin's oxygen-binding curve?

Accepted Answer

The curve shifts to the right, indicating decreased affinity for oxygen.

Question 18

Which of the following best describes the role of carbonic anhydrase in red blood cells?

Accepted Answer

It catalyzes the reversible hydration of CO$$_2 to $$form HCO$$_3^-$$ and H$$^+.$$

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

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