1.Sickle-cell disease is caused by a mutation in beta-chain of hemoglobin that c
ID: 147370 • Letter: 1
Question
1.Sickle-cell disease is caused by a mutation in beta-chain of hemoglobin that changes a charged amino acid to a hydrophobic amino acid. Where in the normal beta-chain would you most likely expect to find this charged amino acid?
a.On the exterior surface of the beta-chain protein
b.In the interior portion of the beta-chain protein, away from water
c.Only at the active site where the beta chain binds oxygen
d.only at the heme-binding site of the beta-chain
e.It is not likely to be found at any of the above place
a.On the exterior surface of the beta-chain protein
b.In the interior portion of the beta-chain protein, away from water
c.Only at the active site where the beta chain binds oxygen
d.only at the heme-binding site of the beta-chain
e.It is not likely to be found at any of the above place
Explanation / Answer
Answer: A point mutation, or single base substitution, is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. Sickle cell anaemia is caused by a point mutation in the -globin chain of haemoglobin in blood cells causing the amino acid glutamic acid to be replaced with the hydrophobic amino acid valine at the sixth position. However, this small change in the primary structure will lead to a significant impact on the protein structure and its functioning, which in turn, affects the shape of haemoglobin.
In normal -globin chain the charged amino acid were found to an exterior surface of the -globin protein because polar and charged amino acid residues are more likely to be found on the surface of soluble proteins where they can interact with water and nonpolar (e.g., amino acid side chains like valine) are more likely to be found in the interior where they are sequestered from the water. This change of one amino acid in the -globin chain, haemoglobin molecules forming long fibres that distort the biconcave, or disc-shaped, red blood cells and assumed to be a crescent or “sickle” shape, which clogs arteries and causes a serious problem. Hence, option (a) is correct
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