A) valine at the 6th position of beta globin chain by glutamine
B) valine at the 6th position of alpha globin chain by glutamic acid
C) glycine at the 6th position of alpha globin chain by glutamic acid
D) glutamic acid at the 6th position of beta globin chain by valine.
Correct Answer: D
Solution :
: Sickle-cell anaemia is an autosomal hereditary disorder in which the erythrocytes become sickle shaped under oxygen deficiency as during strenuous exercise and at high altitudes. As found out by Ingram (1958), haemoglobin-S differs from normal haemoglobin-A in only one amino acid- 6th amino acid of p-chain, glutamic acid, is replaced by valine. During conditions of oxygen deficiency 6th-valine forms hydrophobic bonds with complementary sites of other globin molecules. It distort their configuration. As a result, erythrocytes having haemoglobin- S become sickle-shaped.
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