Fetal hemoglobin (HbF) has a higher oxygen affinity than adult hemoglobin at any given PO2. The molecular basis of this difference is:
- A Gamma globin chains bind 2,3-BPG less avidly than beta chains ✓
- B Gamma chains have a lower p50 due to increased cooperativity between subunits
- C Fetal blood contains higher concentrations of 2,3-BPG than maternal blood
- D Gamma chains lack the proximal histidine required for oxygen binding
Correct answer: A. Gamma globin chains bind 2,3-BPG less avidly than beta chains
Explanation
2,3-BPG stabilizes the tense (deoxy) conformation by binding a central cavity lined by positively charged residues contributed by beta chains. Gamma chains carry serine instead of positively charged histidine at position 143, weakening BPG binding. With less BPG stabilization of the deoxy form, HbF holds oxygen more tightly and its dissociation curve shifts left, allowing oxygen transfer across the placenta from maternal HbA. Total fetal BPG concentration is similar to adult blood.
Reference: Ganong Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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