Peptide

A peptide is a short chain of amino acids linked by peptide bonds, generally defined as containing between two and fifty residues — shorter than a full-length protein.

The peptide bond is an amide linkage formed between the carboxyl group of one amino acid and the amino group of the next, created by a condensation reaction that releases a molecule of water. A chain is read directionally from its free amino (N-) terminus to its carboxyl (C-) terminus, and this sequence determines how the molecule folds and behaves.

The boundary between a peptide and a protein is conventional rather than absolute, generally drawn near fifty residues. Research peptides in this size range are typically produced by solid-phase peptide synthesis and verified for identity by mass spectrometry.