Which of the following amino acid forms sulphide bond in polypeptide

Options

A. Arg
B. Cys
C. Leu
D. Gly

Answer

To determine which amino acid forms disulfide bonds in polypeptides, we need to analyze the structures of the amino acids mentioned in the question. The amino acid that is known for forming disulfide bonds is cysteine.

### Step-by-Step Solution:

1. **Identify the Amino Acids**: The question asks about amino acids that can form sulfide bonds. The primary amino acid known for this function is cysteine.

2. **Understand the Structure of Cysteine**: Cysteine contains a thiol (-SH) group in its side chain. The structure of cysteine can be represented as:
- NH2-CH(COOH)-CH2-SH
- Here, the -SH group is crucial for forming disulfide bonds.

3. **Formation of Disulfide Bonds**: When two cysteine molecules come close together, the thiol groups can undergo oxidation. This reaction leads to the formation of a covalent bond known as a disulfide bond (S-S bond).
- The reaction can be summarized as:
- 2 R-SH → R-S-S-R + 2 H⁺ + 2 e⁻
- This bond is important for stabilizing the three-dimensional structure of proteins.

4. **Conclusion**: Since cysteine is the only amino acid that can form disulfide bonds due to its unique thiol group, it is the correct answer to the question.

### Final Answer:
Cysteine is the amino acid that forms disulfide bonds in polypeptides.

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