Hemoglobin has how many oxygen binding sites?

Hemoglobin has how many oxygen binding sites?

• A. 2
• B. 3
• C. 4
• D. 5

Answer: (C)

Hemoglobin can carry four oxygen molecules because it is a tetramer composed of four subunits, each with a heme group containing an iron atom that binds one O2 molecule. In adults, these subunits are two alpha and two beta chains, but the key point is that there are four heme groups, giving four oxygen-binding sites in total. This capacity remains the same even though binding is cooperative—the first O2 binding increases the affinity for the next, but the maximum number of O2 molecules carried is four.

Hemoglobin can carry four oxygen molecules because it is a tetramer composed of four subunits, each with a heme group containing an iron atom that binds one O2 molecule. In adults, these subunits are two alpha and two beta chains, but the key point is that there are four heme groups, giving four oxygen-binding sites in total. This capacity remains the same even though binding is cooperative—the first O2 binding increases the affinity for the next, but the maximum number of O2 molecules carried is four.