In sickle cell anaemia, an amino acid substitution is

Options

A. valine by glutamine in `alpha`- chain
B. Valine by glutamine in `beta`- chain
C. Glutamine by valine in `alpha`- chain
D. Glutamate by valine in `beta`- chain

Answer

### Step-by-Step Solution:

1. **Understanding Sickle Cell Anemia**:
- Sickle cell anemia is a genetic disorder that affects the shape and function of red blood cells (RBCs). In this condition, the RBCs become sickle-shaped instead of the normal disc shape.

2. **Identifying the Cause**:
- The primary cause of sickle cell anemia is a mutation in the hemoglobin gene, specifically in the beta-globin chain of hemoglobin.

3. **Amino Acid Substitution**:
- In sickle cell anemia, there is a specific amino acid substitution that occurs. The amino acid glutamic acid (Glu) is replaced by valine (Val) in the beta chain of hemoglobin.

4. **Result of the Substitution**:
- This substitution leads to the production of an abnormal form of hemoglobin known as hemoglobin S (HbS). The presence of HbS causes the red blood cells to deform into a sickle shape, especially under low oxygen conditions.

5. **Consequences of Sickle Shape**:
- The sickle-shaped cells are fragile and can break easily, leading to a shortage of healthy red blood cells (anemia) and various complications due to impaired blood flow.

6. **Conclusion**:
- Therefore, the amino acid substitution in sickle cell anemia is the replacement of glutamic acid with valine in the beta chain of hemoglobin.

### Final Answer:
In sickle cell anemia, the amino acid substitution is glutamic acid (Glu) replaced by valine (Val) in the beta chain of hemoglobin.

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