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MBBS QUESTION #10328
Question 1
Hemoglobin S (sickle hemoglobin) differs from normal adult hemoglobin (HbA) due to which molecular change in the beta-globin chain, a change that promotes hemoglobin polymerization under deoxygenated conditions?
  • Substitution of a polar (hydrophilic) glutamate residue with a nonpolar (hydrophobic) valine at position 6 of the beta chain✔️
  • Complete deletion of an entire beta-globin gene
  • A frameshift mutation that truncates the beta-globin chain
  • A structural change confined to the alpha-globin chain rather than beta
Correct Answer Explanation
A single point mutation replaces glutamate with valine at position 6 of the beta-globin chain; this introduces a hydrophobic patch on the hemoglobin surface that, upon deoxygenation, promotes polymerization of HbS molecules into rigid fibers, distorting red cells into the characteristic sickle shape.