Answer: Its gamma chains have lower affinity for 2,3-BPG than beta chains of HbA, maintaining higher O2 saturation.
- A It carries two additional heme groups per tetramer for extra oxygen binding capacity in most textbook accounts
- B Its gamma chains have lower affinity for 2,3-BPG than beta chains of HbA, maintaining higher O2 saturation
- C Its heme prosthetic group uses a different iron oxidation state compared to HbA during normal conditions
- D It dissolves more readily in fetal plasma due to its smaller overall molecular size as generally observed
Correct answer: B. Its gamma chains have lower affinity for 2,3-BPG than beta chains of HbA, maintaining higher O2 saturation
Explanation: HbF (alpha2gamma2) binds 2,3-BPG less strongly than HbA (alpha2beta2). Since 2,3-BPG reduces O2 affinity, HbF has higher O2 affinity, facilitating O2 transfer from maternal to fetal blood.
The S-shaped (sigmoid) curve reflects cooperative binding between Hb's four O₂ sites; the Bohr effect shifts the whole curve to the right under conditions found in actively respiring tissue (more CO₂, more acid, more heat), making haemoglobin release oxygen more readily exactly where it's needed.
Concept context
The mechanics of breathing, lung volumes, gas transport in blood, the Bohr effect, and respiratory regulation.