A) sixth amino acid (from NH^ terminus) of beta chain is glutamic acid
B) erythrocytes elongates and form sickle shaped cells
C) individual homozygous for haemoglobin S allele are\[Hb_{B}^{S}/Hb_{B}^{S}\]
D) beta chain of haemoglobin S contains valine
Correct Answer: C
Solution :
: Sickle cell anaemia is a severe haemolytic anaemia, caused by a mutation in the\[\beta -\] globin gene that changes the sixth amino acid from glutamic acid to valine. Anaemic patients are homozygous for the sickle cell gene which controls the synthesis of sickle cell haemoglobin (HbS) found instead of normal (rounded in shape) HbA in erythrocyte. Under conditions of reduced oxygen pressure, HbS crystallizes into long helical tubes and the erythrocytes distort into a sickle shape clogging capillaries and leading to tissue anoxia. HbS containing erythrocytes also tend to be very fragile, their rapid destruction leads to anaemia.
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