Final answer:
The correct answer to the question is that in HbS (sickle cell hemoglobin), a glutamate residue is replaced by a valine residue, leading to the manifestation of sickle cell anemia.
Step-by-step explanation:
In Hb S, a single amino acid substitution leads to sickle cell anemia. Specifically, the amino acid glutamate at position six in the beta chain of normal hemoglobin is replaced by a hydrophobic amino acid, valine, in sickle cell hemoglobin (HbS). This small change in the primary structure of hemoglobin results in the altered shape of red blood cells, inducing the symptoms associated with sickle cell anemia.
In sickle cell anemia, a glutamate residue is replaced by a valine residue in Hb S. Normal hemoglobin, known as Hb A, has glutamate at position seven in its beta chain. However, in sickle cell hemoglobin, also known as Hb S, this glutamate is substituted by valine.
This single amino acid substitution causes a change in protein structure and function, leading to the formation of abnormal sickle-shaped red blood cells.
The correct answer is: In Hb S, a glutamate residue is replaced by a valine residue.