Q.25 Which of the following factors affects the affinity of hemoglobin for oxygen?
1. pH
2. Temperature
3. Binding of 2,3-bisphosphoglycerate
4. pH, temperature and binding of 2,3-bisphosphoglycerate
Hemoglobin’s affinity for oxygen is modulated by several physiological factors that shift the oxygen-hemoglobin dissociation curve right (decreased affinity, better unloading) or left (increased affinity).
Correct Answer
4. pH, temperature and binding of 2,3-bisphosphoglycerate
All three factors independently decrease Hb-O2 affinity in tissues: low pH (Bohr effect), high temperature, and 2,3-BPG binding stabilize deoxyhemoglobin’s T-state, promoting O2 release where needed.
Option Analysis
pH (Option 1)
Acidosis (low pH) protonates Hb, shifting the curve right via Bohr effect; alkalosis does the opposite—key for active tissues producing lactic acid.
Temperature (Option 2)
Fever/hyperthermia increases molecular motion, reducing affinity (right shift); hypothermia increases it (left shift), aiding O2 loading in lungs.
Binding of 2,3-bisphosphoglycerate (Option 3)
2,3-BPG (or DPG), produced in RBC glycolysis, binds deoxyHb’s central cavity, stabilizing low-affinity state; levels rise in hypoxia/chronic anemia.
All Three Factors (Option 4)
Correct: These classic allosteric effectors collectively optimize O2 delivery—pH/Temp via local tissue changes, 2,3-BPG via adaptive RBC response.
| Factor | Effect on Affinity | Curve Shift | Key Context |
|---|---|---|---|
| pH (low) | Decreases | Right | Acidosis/exercise |
| Temperature (high) | Decreases | Right | Fever/activity |
| 2,3-BPG (high) | Decreases | Right | Hypoxia/anemia |
| Combined | All decrease | Right | Tissue O2 unloading |
Clinical Relevance
These shifts explain efficient O2 transport in exams like NEET-PG; e.g., right shift in exercising muscle ensures delivery despite normal PaO2.
