Sickle-cell anemia is a genetic blood disorder that results from a point mutatio

Question

Sickle-cell anemia is a genetic blood disorder that results from a point mutation in hemoglobin.
Hemoglobin is a protein made of four subunits: two alpha chains and two beta chains. A mutation in the
gene for the beta subunit changes an E at amino acid position 6 to a V. This change causes the
hemoglobin molecules to polymerize, forming fibers under low blood oxygen conditions.

a) Explain how a single amino acid change can cause such a large effect on protein structure.

b) Below is a graph of the binding curves for fetal hemoglobin and adult hemoglobin. Explain the major
difference(s) between fetal and adult hemoglobin.

c) List two major differences between myoglobin and hemoglobin.

Explanation / Answer

1. Change in the single amino acis is called as Point Mutation or Single Base Modification. This is a type of mutation that causes a single nucleotide base substitution , insertion or deletion of the genetic material, DNA or RNA.The term Frameshift mutation indicated addition or deletion of a base pair. What happens is that if the single nucleotide is changed then there is change in the entire sequence of the codon so it becomes a different codon. Thus if it becomes a different then the amino acid chain which forn=ms is also different therefore the protein structure formed will be different.

2. Fetal Haemoglobin is the main Oxygen transport protein in the Foetus during the last sevsn months of the development in the Uterus. Functionally, the fetal Hemoglobin differs much from the Adult hemoglobin, in that it is able to bind with Qxygen at a greater affinity than the Dault hemoglobin so that the fetus can have a better access to Oxygen from the mother's blood stream. B. fetal hemoglobin is composed of two beta and two gamma subunits where as adult hemoglobin is made of two alpha and two beta subunit.

3. Myoglobin is a monomeric protein and binds the molecular Oxygen and carries it to the muscle tissue, Whereas Hemoglobin is a tetrameric protein and binds molecular Oxygen to RBCs.

Myoglobin consists of 8 right handed alpha helices and each protein molecule contain one heme prosthetic group and each heme residue contain one central coordinately bound Iron Atom.Whereas, in Hemoglobin its 2 alpha and 2 beta subunits.

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