months, normal adult hemoglobin A is the dominant hemoglobin (Devlin 1030). Hemoglobin F is adapted to the environment in the womb, where the fetus gets most of its oxygen from the mother, which is a far poorer source than the atmosphere (Devlin 1030). To compensate for this, the fetus needs a hemoglobin with a higher oxygen-binding capacity (Devlin 1030).
In hemoglobin F, two of the 2,3,-biphosphoglycerate (BPG)-binding cavities have neutral side chains, so it binds BPG less tightly and oxygen more tightly than hemoglobin A, which has two positively charged BPG binding sit
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