An antibody contains light and heavy chains interconnected by disulphide bonds. These disulphide bonds can be formed between

Options

A. serine, theonine
B. methionine, cysteine
C. methionine, methionine
D. cysteine, cysteine

Answer

To solve the question regarding the formation of disulfide bonds in antibodies, we will analyze the options provided and understand the role of specific amino acids in the formation of these bonds.

### Step-by-Step Solution:

1. **Understanding Antibody Structure**:
- Antibodies are proteins composed of heavy and light chains. These chains are linked together by disulfide bonds, which are crucial for maintaining the structural integrity of the antibody.

2. **Identifying Disulfide Bonds**:
- Disulfide bonds are covalent bonds formed between the sulfur atoms of cysteine residues. This means that for disulfide bonds to form, the amino acids involved must contain sulfur.

3. **Analyzing the Options**:
- The options given are:
- A) Serine, Threonine
- B) Methionine, Cysteine
- C) Methionine, Methionine
- D) Cysteine, Cysteine

4. **Evaluating Each Option**:
- **Option A (Serine, Threonine)**: Both of these amino acids do not contain sulfur, hence cannot form disulfide bonds. This option is incorrect.
- **Option B (Methionine, Cysteine)**: While methionine contains sulfur, it does not participate in the formation of disulfide bonds in antibodies. Cysteine is the amino acid that forms disulfide bonds. This option is incorrect.
- **Option C (Methionine, Methionine)**: This option does not contain any cysteine, and thus cannot form disulfide bonds. This option is incorrect.
- **Option D (Cysteine, Cysteine)**: Cysteine is the only amino acid that can form disulfide bonds with another cysteine. Therefore, this option is correct.

5. **Conclusion**:
- The correct answer is **D) Cysteine, Cysteine**, as disulfide bonds in antibodies are formed between cysteine residues.