peptide

Peptides comprise linked amino acids in specific sequences. Peptides differ from proteins, which are chains of hundreds of amino acids, in being less than 50 amino acids in length. Three large classes of peptides are recognized: ribosomal peptides, nonribosomal peptides, and digested peptides.

Ribosomal peptides sequences are genetically coded, and they are synthesized at the endoplasmic reticulum by translation of mRNA. Often proteolysis generates the mature form. Ribosomal peptides function as hormones and signalling molecules.

Digested peptides are the result of nonspecific proteolysis as part of the digestive cycle.

Nonribosomal peptides are confined primarily to unicellular organisms, plants, and fungi. They are synthesized using a modular enzyme complex.