Fetal haemoglobin (HbF) has a higher oxygen affinity than adult HbF (HbA). The physiological reason for this is:
- A HbF has a higher Bohr effect allowing more O2 loading in fetal lungs
- B HbF has 4 gamma chains which directly bind O2 more tightly than beta chains
- C HbF binds 2,3-DPG less avidly than HbA, resulting in a left-shifted ODC ✓
- D Lower pH in fetal blood shifts the oxygen dissociation curve leftward
Correct answer: C. HbF binds 2,3-DPG less avidly than HbA, resulting in a left-shifted ODC
Explanation
HbF (α2γ2) binds 2,3-DPG less avidly than HbA (α2β2) because the gamma chains lack the positively charged histidine residue at position 143 (beta-143 His) that provides a key 2,3-DPG binding site. Since 2,3-DPG stabilizes the deoxy (T) conformation of Hb, less DPG binding means HbF has higher oxygen affinity (left-shifted ODC). This is crucial for placental gas exchange, allowing HbF to extract O2 from maternal HbA across the placenta.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.