What type of bond joins amino acids to form polypeptides?

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

Answer: (A)

Amino acids are joined into a polypeptide by a covalent linkage called a peptide bond, an amide bond formed between the carboxyl group of one amino acid and the amino group of the next. This connection is made through a dehydration synthesis reaction, releasing a molecule of water. The peptide bond has partial double-bond character due to resonance, which makes the backbone rigid and planar and helps align the amino acids in a long chain that can then fold into complex protein structures.

Other types of bonds play different roles in protein structure but aren’t the main link between amino acids in the chain. Hydrogen bonds help stabilize secondary structures like alpha helices and beta sheets. Ionic bonds are electrostatic interactions between charged side chains. Disulfide bonds form covalent links between cysteine residues to stabilize the overall structure, but they occur later in the protein’s architecture rather than linking the amino acids together to form the backbone.