Fetal hemoglobin (HbF) has higher oxygen affinity than adult HbF (HbA). Which molecular property of HbF accounts for its LEFT-shifted oxygen dissociation curve?
- A HbF contains alpha chains that bind oxygen with intrinsically higher affinity
- B HbF operates at lower temperature in the fetal environment reducing oxygen release
- C HbF gamma chains bind 2,3-DPG less avidly than adult beta chains, maintaining HbF in R (oxy) state ✓
- D HbF has a higher Bohr effect allowing oxygen release at lower pH
Correct answer: C. HbF gamma chains bind 2,3-DPG less avidly than adult beta chains, maintaining HbF in R (oxy) state
Explanation
The key difference is that HbF has gamma (γ) subunits instead of adult beta (β) subunits. The gamma subunits have a lower binding affinity for 2,3-DPG compared to beta subunits. Since 2,3-DPG stabilizes the T (deoxy) state of hemoglobin and shifts the ODC rightward, reduced 2,3-DPG binding by HbF means HbF remains more in the R (oxy) conformation — giving it a higher O2 affinity and a left-shifted ODC. This allows HbF to extract oxygen from maternal HbA at the placenta (the Haldane-Bohr double effect). Options B, C, and D are incorrect mechanisms.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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