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MBBS QUESTION #10301
Question 1
Hemoglobin is one of the most important intracellular/protein buffers in the body, particularly within red blood cells buffering the hydrogen ions generated from CO2 hydration. This buffering capacity is largely attributable to which amino acid's side chain, whose pKa lies close to physiological pH?
  • Histidine (imidazole side chain)✔️
  • Glycine
  • Alanine
  • Leucine
Correct Answer Explanation
The imidazole ring of histidine has a pKa close to physiological pH, making histidine-rich proteins like hemoglobin excellent physiological buffers — a property exploited by red blood cells to buffer H+ generated as carbonic anhydrase converts CO2 and water to carbonic acid during tissue CO2 uptake.