Question

Hemoglobin is a complex protein that contains four polypeptide chains. The normal hemoglobin found in adults, called adult hemoglobin, consists of two alpha and two beta polypeptide chains, which are encoded by different loci. Sickle‑cell hemoglobin, which causes sickle‑cell anemia, arises from a single mutation in the beta chain of adult hemoglobin. Adult hemoglobin and sickle‑cell hemoglobin differ in a single amino acid. The sixth amino acid from one end in adult hemoglobin is glutamic acid, whereas sickle‑cell hemoglobin has valine at this position.
1. After consulting a codon table, indicate the mutant codons that could give rise to sickle-cell anemia.

a) GUC
b) GAA
c) GUG
d) GUA
e) GAG

2. Indicate the type of mutation that gave rise to sickle-cell anemia.

A) a frameshift that results from a two-base deletion
B) a transversion that leads to a nonsense mutation
C) a transition that leads to a missense mutation
D) a transversion that leads to a missense mutation
E) a transition that leads to a neutral mutation

Answer 1

Answer:

1) A, C and D

2) D

Explanation:

The normal hemoglobin is made up of heme and globin. The protein, globin is in turn made up of four polypeptide chains which include two alpha and two beta chains.

The gene gene responsible for the creation of the beta globin chain is located on the short arm of chromosome eleven. It is called the HBB gene. Many mutations occur on the HBB gene and a mutation on this gene produces abnormal hemoglobin like HBS, hbc, and hbe. HBs causes sickle cell anemia.

In sickle cell anemia, there is an alteration of the genetic code, leading to the substitution of a single amino acid where glutamic acid is replaced by valine in the sixth position of the beta chain.

In the mRNA, the change converts a glutamic acid codon(GAG or GAA) to a valine codon(GUA, GUC, GUU or GUG).

Sickle cell anemia is caused by a transversion that leads to a missense mutation.