What unique component does adult hemoglobin have that fetal hemoglobin lacks?

Adult hemoglobin contains 2,3-diphosphoglycerate (DPG), while fetal hemoglobin does not. DPG plays a crucial role in modulating the affinity of hemoglobin for oxygen. In adult hemoglobin, the presence of DPG reduces the oxygen affinity, allowing for more efficient oxygen release to tissues that require it, especially during periods of higher metabolic activity. The absence of DPG in fetal hemoglobin enables it to have a higher affinity for oxygen, which is essential for the developing fetus to extract oxygen from maternal blood.

This differential binding and affinity characteristic allows fetal hemoglobin to effectively compete for oxygen and ensures the fetus receives adequate oxygenation from the mothers’ supply, which is particularly important given the conditions of their circulatory system.