Question

Amino acid substituted in sickle cell anaemia is

• A. Glutamic acid for valine in $\alpha$-chain
• B. Glutamic acid for valine in $\beta$-chain
• C. Valine for glutamic acid in $\alpha$-chain
• D. Valine for glutamic acid in $\beta$-chain

Answer 1

The correct option is D Valine for glutamic acid in $\beta$-chain

Haemoglobin has four protein subunits, two $\alpha$-globin and two $\beta$-globin. The $H{b}^b$ gene codes the $\beta$ chain. A missense mutation, replacement of A by T at the 17th nucleotide of the $H{b}^b$ gene changes the codon GAG (glutamic acid) to GTG (which encodes valine). The mutated allele $H{b}^s$ encodes the abnormal haemoglobin molecules which stick to one another and cause stiffness and sickle shape of red blood cells. The function of haemoglobin is to transport oxygen from the lungs to other parts of the body. The sickle-shaped RBC block and damage the vital organs and tissue.