Question

Which of the following factors raise the P50 and shifts the HbO2 dissociation curve to right and vice versa?
a. Rise in \[pC{O_2}\]
b. Fall in temperature
c. Rise in \[{H^ + }\] (=fall in pH)
d. Fall in diphosphoglyceric acid
A) a and b are correct
B) b and d are correct
C) a and c are correct
D) a, b and c are correct

Answer 1

Hint: About 98.5% of the blood oxygen is bound to hemoglobin in red blood cells. Oxygen and hemoglobin bind in a reversible reaction to make oxyhemoglobin. This reaction between oxygen and hemoglobin is known as oxygenation.

Complete answer:
Oxygen binding to hemoglobin is explained by a sigmoid or S-shaped curve. This indicates the hemoglobin exhibits a special binding behavior. The binding of oxygen to hemoglobin is cooperative, that is, as oxygen is bound to one subunit, the binding of other subunits is facilitated. The \[p{O_2}\] is the most important factor that determines the percent oxygen saturation of hemoglobin. However, there are several other factors that can affect the affinity, with which hemoglobin binds with oxygen. As a result, these factors can shift the entire curve either to the left (higher affinity) or to the right (lower affinity).
Lowering the pH causes the oxygen affinity of hemoglobin to decrease and shifts the curve to the right. Thus, a higher \[p{O_2}\] is required for hemoglobin to bind the given amount of \[{O_2}\]. This effect of pH on oxygen affinity of Hemoglobin is known as the Bohr Effect.
Similarly, in presence of higher \[pC{O_2}\], hemoglobin binds with \[C{O_2}\] to form carboxyhemoglobin. This decreases the oxygen affinity of hemoglobin causing the curve to shift right. An increase in temperature can be another contributing factor as with a rise in temperature, the binding capacity of \[{O_2}\] also decreases.

The correct answer is option C, stating a and c are correct.

Note:
One hemoglobin molecule binds four molecules of oxygen, one per heme. This oxygen is then carried to different cells or tissues or organs. Molecules like carbon monoxide and nitric oxide may also bind to the heme iron.