Question

Amino acid that can form Di-sulfide linkage in protein

• A. Leucine
• B. Glycine
• C. Serine
• D. Cysteine

Hint:

To remember which amino acid forms disulfide bonds, think "Cysteine creates connections." The "S" in Cysteine can also remind you of Sulfur. (Note: Methionine also contains sulfur, but its sulfur is in a thioether group, C-S-C, which cannot form disulfide bonds).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
A disulfide linkage (also called a disulfide bridge or bond) is a covalent bond formed between two sulfur atoms. In proteins, this type of bond is crucial for stabilizing the tertiary and quaternary structures. It is formed by the oxidation of the side chains of two specific amino acid residues.
Step 2: Detailed Explanation:
We need to identify the amino acid that has a sulfur-containing side chain capable of forming a disulfide bond. Let's examine the side chains (R-groups) of the given amino acids:
Leucine: The side chain is -CH\(_2\)CH(CH\(_3\))\(_{2}\), an isobutyl group. It contains only carbon and hydrogen.
Glycine: The side chain is simply a hydrogen atom, -H.
Serine: The side chain is -CH\(_2\)OH, containing a hydroxyl group.
Cysteine: The side chain is -CH\(_2\)SH, containing a sulfhydryl or thiol group (-SH).
The formation of a disulfide bond is an oxidation reaction between two thiol groups: \[ \text{R-SH} + \text{HS-R'} \xrightarrow{\text{[Oxidation]}} \text{R-S-S-R'} + 2H^+ + 2e^- \] Only cysteine, with its thiol group, can participate in this reaction. Two cysteine residues can be oxidized to form a single cystine residue, linked by a disulfide bond.
Step 3: Final Answer:
Cysteine is the amino acid whose side chain contains a sulfhydryl group, which can be oxidized to form a disulfide linkage.