Hemoglobin S is an abnormal hemoglobin that is characterized by a substitution of which amino acid?

Hemoglobin S is an abnormal hemoglobin that is characterized by a substitution of which amino acid?

• A. Valine for glutamic acid in position 6 on the beta chain
• B. Valine for glutamic acid in position 6 on the alpha chain
• C. Lysine for glutamic acid in position 6 on the beta chain
• D. Lysine for glutamic acid in position 6 on the alpha chain

Answer: (A)

Sickle hemoglobin results from a single amino acid change in the beta-globin chain. The normal glutamic acid, which is negatively charged, is replaced by valine, a hydrophobic amino acid, at the sixth position of the beta chain. This alters the surface properties of the hemoglobin molecule, and when oxygen is released (deoxygenated state), HbS tends to polymerize, forming long fibers that distort red blood cells into a sickle shape. That polymerization and solid-state change under low oxygen is what drives the characteristic sickling and its downstream effects. This change occurs specifically in the beta chain, not the alpha chain, and it is valine substituting for glutamic acid, not lysine.

Sickle hemoglobin results from a single amino acid change in the beta-globin chain. The normal glutamic acid, which is negatively charged, is replaced by valine, a hydrophobic amino acid, at the sixth position of the beta chain. This alters the surface properties of the hemoglobin molecule, and when oxygen is released (deoxygenated state), HbS tends to polymerize, forming long fibers that distort red blood cells into a sickle shape. That polymerization and solid-state change under low oxygen is what drives the characteristic sickling and its downstream effects.

This change occurs specifically in the beta chain, not the alpha chain, and it is valine substituting for glutamic acid, not lysine.