The bonds that join amino acids in a growing polypeptide chain are called what?

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

Answer: (C)

Peptide bonds are covalent linkages that join amino acids in a growing polypeptide chain. They form via a condensation reaction when the carboxyl group of one amino acid reacts with the amino group of the next, releasing a molecule of water. This linkage creates a stable amide bond between the carbonyl carbon of one residue and the nitrogen of the next, forming the protein backbone. The bond has partial double-bond character from resonance, which makes it planar and limits rotation around that bond, helping determine how the polypeptide folds. Other types of bonds—hydrogen bonds, ionic bonds, and disulfide bonds—play distinct roles: hydrogen bonds stabilize secondary structures like helices and sheets, ionic bonds occur between charged side chains, and disulfide bonds cross-link cysteine residues to reinforce three-dimensional structure but do not link consecutive amino acids in the main chain.