For the development of sickle cell disease, codon of aminoacid glutamate is replaced with codon of amino acid_____ at the 6th position of beta globin gene –
**Core Concept**
Sickle cell disease is a genetic disorder caused by a mutation in the beta-globin gene, leading to the production of abnormal hemoglobin (HbS). This mutation results in the substitution of a single amino acid, which alters the structure and function of hemoglobin.
**Why the Correct Answer is Right**
The beta-globin gene contains a codon for glutamic acid (GAG) at the 6th position. In sickle cell disease, this codon is replaced by a codon for valine (GTG) due to a point mutation. This substitution leads to the production of HbS, which has a hydrophobic valine residue instead of the hydrophilic glutamic acid residue. As a result, HbS polymerizes under deoxygenated conditions, causing red blood cells to take on a characteristic sickle shape.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the mutation in the beta-globin gene associated with sickle cell disease.
**Option B:** Valine is the correct answer, but lysine is not the amino acid replaced by glutamate in sickle cell disease.
**Option C:** This option is not relevant to the mutation in the beta-globin gene associated with sickle cell disease.
**Clinical Pearl / High-Yield Fact**
The substitution of valine for glutamic acid at the 6th position of the beta-globin gene is a classic example of a point mutation, which can lead to significant changes in protein function and structure. This mutation is responsible for the development of sickle cell disease, a condition that affects millions of people worldwide.
**Correct Answer: C. Valine**