Question

Disulfide bonds are identified using the distance between the side-chains of which one of the following sulphur-containing residue pairs?

• A. Cys and Met
• B. Cys and Cys
• C. Met and Met
• D. Met and His

Hint:

Only Cysteine makes the "bridge." Methionine is too stable to form these covalent links.

Answer 1

The Correct Option is B

Step 1: Concept
A disulfide bond is a covalent bond formed between the thiol (-SH) groups of two sulphur-containing amino acid residues.

Step 2: Residue Identification
Cysteine (Cys) contains a highly reactive thiol group. Methionine (Met) also contains sulphur, but it is in the form of a thioether, which does not form disulfide bridges.

Step 3: Analysis
Disulfide bonds occur specifically when two Cysteine residues are in close proximity and undergo oxidation.

Step 4: Conclusion
The correct pair is Cys and Cys. Final Answer: (B)