Disulfide bridges contribute to stabilizing which level of protein structure?

• A. Primary
• B. Secondary
• C. Tertiary
• D. Quaternary

Answer: (B)

Disulfide bridges are covalent bonds between cysteine side chains that act as molecular staples, locking distant parts of a protein together to maintain its folded three-dimensional shape. This strengthens the overall conformation of the molecule, which is the tertiary structure. Secondary structure—alpha helices and beta sheets—is stabilized mainly by hydrogen bonds along the backbone, not by these crosslinks, so disulfide bonds don’t primarily reinforce those local patterns. In proteins with multiple polypeptide chains, disulfide bonds can also link different chains, contributing to quaternary structure stability, but their classic role is to stabilize the folded tertiary form overall.