Q2. The following questions are based on sickle cell anemia, a striking example
ID: 52870 • Letter: Q
Question
Q2. The following questions are based on sickle cell anemia, a striking example of a genetic disease caused by single amino acid substitution that drastically affects the structure and function of hemoglobin.
A) Given the chemical nature of glutamate and valine, why substitution of valine at position 6 of the b chain of hemoglobin is deleterious?
B) What are other amino acids that would be much less likely than valine to cause impairment of hemoglobin function if substituted for glutamate at position 6 of the b chain?
C) Explain why, in some cases, two proteins could differ at several points in their amino acid sequence and still be very similar in structure and function?
Explanation / Answer
Sickle cell anemia is a blood disorder witnessed by improper folding of hemoglobin when hemoglobin levels are low and affects the oxygen carrying capacity of an individual.
Sickle cell anemia is caused by mutation in the protein hemoglobin. The point mutation is caused in -globin chain of hemoglobin. This result in placing of hydrophobic amino acid valine in place of hydrophilic amino acid glutamic acid, taking place at the sixth position. Sickle cell anemia is serious condition with a high mortality rate.
Note: The provided nucleotide sequence is DNA.
Based on the molecular analysis of in gene that codes for -globin chain of hemoglobin, the GAG at 6th position codes for glutamic acid and the middle base “A” (adenine) is replaced with T (Thymine), which results change in the sequence GAG to GTG. Hence, the GTG codes for Valine. This mutation is called point mutation.
A)
The glutamic acid is a hydrophilic amino acid it is replaced by a hydrophobic amino acid called valine. Thus, change in the amino acids results change in the hydro properties in the -globin chain of hemoglobin, and it leads to aggregation of the RBC, and form tetramers. These tetramers cannot bind to oxygen, thus due to deprivation oxygen makes the RBC to attain sickle cell shape.
B)
Arginine, serine, glycine, proline, aspartate and tryptophan are the amino acids that would be much less likely than valine to cause impairment of hemoglobin function if substituted for glutamate at position 6 of the beta-chain.
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