peptide bond n. The chemical bond formed between the carboxyl groups and amino groups of neighboring amino acids, constituting the primary linkage of all protein structures. peptide bond. The chemical bond formed between amino acids, constituting the primary linkage in all protein structures. In a peptide bond, the carboxyl group (COOH) of one amino acid bonds with the amino group (NH2) of another, forming the sequence CONH and releasing water (H2O).