The oxygen-binding curves for nomral hemoglobin (HbA) and a mutant hemoglobin (H

Question

The oxygen-binding curves for nomral hemoglobin (HbA) and a mutant hemoglobin (Hb Great Lakes) are shown in the figure above.

(a) Compare the shapes of the curves for the two hemoglobins and comment on their significance.
(b) Which hemoglobin has a higher affinity for oxygen when pO2 = 20 torr? (1 torr = 1 mm Hg; 1 atm = 760 mmHg or 760 torr)

(c) Which hemoglobin has a higher affinity for oxygen at pO2 = 75 torr?
(d) Which hemoglobin is most efficient at delivering oxygen from arterial blood (pO2 = 75 torr) to active muscle (pO2 = 20 torr)?

Explanation / Answer

a) HbA -oxygen binding curve is sigmodal and HbGL-oxygen binding curve obeys a power law. In sigmoidal, at low and high oxygen pressures, the affinity varies little compared to that at moderate pressures. However in power law, the affinity varies little when it becomes saturated at higher pressures.

b) At 20 torr, HbA-oxygen binding affinity, Y is about 03 and that for HbGL-oxygen binding is about 0.6. HbGL has higher binding affinity.

c) At 75 torr, the affinity for both proteins reaches a saturation point at little less than 1.0.

d) HbA is more efficient in delivering oxygen from arterial blood to active muscle as at 20 torr, its binding affinity to oxygen is lower and hence releases bound oxygen more.

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