Which of the following is correct for HbS peptide molecule?

Options

A. Val-His-Leu-Pro-Thr-Val-Glu
B. Val-His-Leu-Thr-Pro-Val-Glu
C. Val-His-Thr-Leu-Pro-Glu-Val
D. Val-His-Leu-Thr-Pro-Glu-Glu

Answer

To determine which of the following is correct for the HbS peptide molecule, we will analyze the structure of the HbS hemoglobin variant and the specific amino acid substitutions that occur due to genetic mutations.

### Step-by-Step Solution:

1. **Understand the Mutation**:
- The HbS (Hemoglobin S) variant is caused by a mutation in the hemoglobin gene where glutamic acid is replaced by valine at the sixth position of the beta-globin chain. This is a result of a single nucleotide substitution from GAG to GUG.

2. **Identify the Amino Acid Sequence**:
- The normal hemoglobin (HbA) sequence at the sixth position is glutamic acid (Glu), while in HbS, it is valine (Val). The sequence of the HbS peptide molecule starts with:
- 1st position: Valine (Val)
- 2nd position: Histidine (His)
- 3rd position: Leucine (Leu)
- 4th position: Threonine (Thr)
- 5th position: Proline (Pro)
- 6th position: Valine (Val)
- 7th position: Glutamic acid (Glu)

3. **Evaluate the Options**:
- Now we will evaluate the provided options against the identified sequence:
- **Option 1**: Valine, Histidine, Leucine, Threonine, Proline, Valine, Glutamic acid - This option is incorrect because it lists threonine at the fourth position instead of the correct sequence.
- **Option 2**: Valine, Histidine, Leucine, Threonine, Proline, Valine, Glutamic acid - This option is correct as it matches the sequence we identified.
- **Option 3**: Valine, Histidine, Threonine, Leucine, Proline, Glutamic acid, Valine - This option is incorrect because it incorrectly places threonine at the third position.
- **Option 4**: Valine, Histidine, Leucine, Threonine, Proline, Glutamic acid, Glutamic acid - This option is incorrect as it repeats glutamic acid at the end instead of valine.

4. **Conclusion**:
- The correct option for the HbS peptide molecule is **Option 2**.