The primary defet which leads to sickle cell anemia is -

Ans. is 'b' i.e., Replacement of glutamate by valine in b chain of HBA Sickle cell anemia Sickle cell anemia is a hereditary hemoglobinopathy, i.e. the type of disease characterized by production of defective hemoglobin. Normal hemoglobin o The hemoglobin molecule is an assembly of four globular protein. o Each subunit is composed of a protein pa, i.e. globin and a nonprotein pa, i.e. heme, i.e. Each hemoglobin molecule contains four heme units and two pairs of similar protein, globin. o The heme pa of globular protein is same in all types of hemoglobin. o The protein pa vary in different hemoglobin ? 1. Adult hemoglobin (Hemoglobin A) consist of two identical alpha-chains and two identical alpha-chains. 2. Fetal hemoglobin (HbF) consists of two identical a-chains and two identical y chains. 3. Minor hemoglobin (HbA,) consist of two identical a-chains and two identical S chains. o Normally adult blood contains about 96% of HbA (a,(32)3-3.5% HbA2 (a2O2), and small amount of fetal hemoglobin HbF (.272). Defect in sickle cell anemia Sickle cell anemia results from mutation in fI-globin gene. o It is caused by a point mutation at the sixth position of the beta-globin chain leading to substution of a valine residue for a glutamic acid residue. resulting in sickle hemoglobin (HbS). Sickle cell anemia is an autosomal recessive disorder. o If an individual is homozygous for the sickle cell mutation, almost all the hemoglobin in the red cell is HbS. o In heterozyogotes, only about 40% of the hemoglobin is HbS, the remainder being normal hemoglobins.