In sickle cell disease: September 2007
Ans. B: Glutamtic acid, at position No.6 of beta-globin chain of haemoglobin is replaced by valine Sickle haemoglobin (HbS) is a structural variant of haemoglobin in which glutamic acid, an amino acid, at position No.6 of beta-globin chain of haemoglobin is replaced by valine. This happens due to change of a nucleotide, adenine to thymine (GAGgGTG) of codon 6 of beta-globin gene. This substitution of amino acid changes the net charge of haemoglobin, oxygen affinity and three-dimensional structure thus rendering it as unstable haemoglobin. Sickle haemoglobin gets polymerized at low oxygen tension and deforms the red blood cell from discoid shape to sickle like (crescent) form
Glutamtic acid, at position No.5 of beta-globin chain of haemoglobin is replaced by valine
Glutamtic acid, at position No.6 of beta-globin chain of haemoglobin is replaced by valine
Valine at position No.6 of beta-globin chain of haemoglobin is replaced by glutamtic acid
Valine at position No.5 of beta-globin chain of haemoglobin is replaced by glutamtic acid