Sickle cell anaemia is caused by the substitution of Glu by ………... at the sixth position of the beta-globin chain of the hemoglobin molecule.

Options

A. Asn
B. Gly
C. Arg
D. Val

Answer

To solve the question regarding sickle cell anemia and the substitution of glutamic acid at the sixth position of the beta-globin chain of hemoglobin, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Sickle Cell Anemia**:
Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene. It is characterized by the distortion of red blood cells into a sickle shape.

**Hint**: Remember that sickle cell anemia is a genetic mutation affecting hemoglobin.

2. **Identifying the Mutation**:
The mutation in sickle cell anemia is a point mutation, which means it involves a change in a single nucleotide in the DNA sequence.

**Hint**: Point mutations can lead to the substitution of one amino acid for another in a protein.

3. **Recognizing the Amino Acid Substitution**:
In the case of sickle cell anemia, the amino acid glutamic acid (Glu) at the sixth position of the beta-globin chain is replaced by another amino acid.

**Hint**: Focus on the specific position of the amino acid in the hemoglobin structure.

4. **Determining the Substituted Amino Acid**:
The normal codon for glutamic acid is GAG, which is changed to GUG due to the mutation. The codon GUG codes for valine (Val).

**Hint**: Look at the codon change to identify which amino acid is produced instead of glutamic acid.

5. **Conclusion**:
Therefore, the correct answer to the question is that glutamic acid is substituted by valine at the sixth position of the beta-globin chain of hemoglobin.

**Final Answer**: Valine (Option D).

### Summary:
Sickle cell anemia is caused by the substitution of glutamic acid by valine at the sixth position of the beta-globin chain of hemoglobin.