Question

Two Mark Questions :
A relevant portion of $\beta$-chain of haemoglobin of a normal human is
Val-His-Leu-Thr-Pro-Glu-Glu
1 2 3 4 5 6 7
The codon for the sixth amino acid is GAG. It mutates to GAA due to mutation 'A' and GUG due to mutation 'B'. Haemoglobin structure did not change as a result of mutation 'A' but mutation 'B' led to sickle cell-shaped RBCs. Explain giving reasons how could mutation 'B' change the haemoglobin structure and not mutation 'A'.

Answer 1

In case of mutation A, Glutamine (GAG) in the sixth position changes to GAA which is also a codon for Glutamine. So, there is no overall change in the structure of the RBC.

In case of mutation B, Glutamine (GAG) changes to Valine (GUG), which elongated the RBC due to oxygen tension as the haeomglobin synthesised is faulty and cannot carry sufficient oxygen. This leads to sickle shaped RBCs.