What type of bonds link amino acids to form polypeptide chains?

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

Answer: (A)

Amino acids in a chain are joined by a peptide bond. This covalent linkage forms when the amino group of one amino acid reacts with the carboxyl group of the next, releasing a water molecule in a dehydration synthesis reaction. The result is a repeating backbone of N-C-C units that holds the primary sequence together. The peptide bond has partial double-bond character, making it planar and limiting rotation, which helps define the overall shape of the protein’s backbone.

Other types of bonds play different roles. Ionic bonds form between charged side chains or molecules and help with interactions in and between proteins, but they don’t form the main chain. Hydrogen bonds stabilize secondary structures like alpha helices and beta sheets. Disulfide bonds link cysteine residues and can cross-link different parts of a protein, stabilizing the folded structure, but they are not the bonds that connect successive amino acids in the polypeptide backbone.