Question

Hemoglobin is 50% saturated with oxygen when pO2 = 26 torr. If hemoglobin exhibited hyperbolic binding (as myoglobin does) with 50% saturation at 26 torr. Which of the following statements is correct? (pO2 =100 in the lungs and pO2 = 30 in the tissues; fractional saturation YO2 = pO2 / {K + pO2} and K=p50=pO2 when YO2=0.5)

a) Hemoglobin exhibits positive cooperativity
b) Hemoglobin follows Michaelis-Menten kinetics
c) Hemoglobin exhibits negative cooperativity
d) Hemoglobin follows a linear binding curve

Answer 1

The correct statement is that hemoglobin exhibits positive cooperativity, which explains its sigmoidal oxygen dissociation curve.

Step-by-step explanation:

Hemoglobin's oxygen-binding affinity and its behavior in response to changes in oxygen partial pressure can be understood through its oxygen dissociation curve. When hemoglobin is 50% saturated with oxygen at a pO2 of 26 torr and exhibits a sigmoidal or S-shaped oxygen dissociation curve, it is indicative of positive cooperativity. This implies that the binding of the first oxygen molecule to hemoglobin increases the affinity for the subsequent oxygen molecules, which then bind more easily until the hemoglobin is fully saturated. On the other hand, myoglobin follows hyperbolic binding kinetics, reflecting a different, non-cooperative mode of oxygen binding.

In answering the student's question, the correct statement is: hemoglobin exhibits positive cooperativity (a). This is because hemoglobin's ability to bind oxygen is influenced by the binding status of its other subunits, leading to a cooperative interaction that is characteristic of its sigmoidal oxygen dissociation curve.