Which statement accurately describes HbS substitution?

Which statement accurately describes HbS substitution?

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

Answer: (A)

The main idea is that HbS results from a single amino acid change in the beta-globin chain: the sixth residue, normally glutamic acid, is replaced by valine. This Glu-to-Val substitution introduces a hydrophobic patch on deoxygenated hemoglobin, promoting abnormal interactions that cause hemoglobin to polymerize and red cells to sickle. That exact description—valine substituting for glutamic acid at position 6 on the beta chain—matches HbS. The other statements would place the substitution on the alpha chain, or replace Glu with lysine, or refer to the wrong chain and position, which do not describe the HbS mutation.

The main idea is that HbS results from a single amino acid change in the beta-globin chain: the sixth residue, normally glutamic acid, is replaced by valine. This Glu-to-Val substitution introduces a hydrophobic patch on deoxygenated hemoglobin, promoting abnormal interactions that cause hemoglobin to polymerize and red cells to sickle.

That exact description—valine substituting for glutamic acid at position 6 on the beta chain—matches HbS. The other statements would place the substitution on the alpha chain, or replace Glu with lysine, or refer to the wrong chain and position, which do not describe the HbS mutation.