What type of bonds are formed when two sulfur-type chains are together?

• A. Hydrogen bonds
• B. Ionic bonds
• C. Disulfide bonds
• D. Metallic bonds

Answer: (C)

When two sulfur-containing side chains come together, they can form a covalent linkage called a disulfide bond. This happens when two thiol groups (-SH) from cysteine residues are oxidized to form an S–S bond, creating a cross-link that helps stabilize protein structure. Hydrogen bonds are noncovalent attractions involving hydrogen linked to electronegative atoms, and ionic bonds are electrostatic attractions between charged groups; neither involves a covalent S–S connection. Metallic bonds are a feature of metals, not organic sulfur chemistry. So the sulfur-to-sulfur covalent bridge formed is a disulfide bond.