[4] Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides.
Peptides fall under the broad chemical classes of biological polymers and oligomers, alongside nucleic acids, oligosaccharides, polysaccharides, and others.
[8] Peptides frequently have post-translational modifications such as phosphorylation, hydroxylation, sulfonation, palmitoylation, glycosylation, and disulfide formation.
[12] These complexes are often laid out in a similar fashion, and they can contain many different modules to perform a diverse set of chemical manipulations on the developing product.
Since the system is closely related to the machinery for building fatty acids and polyketides, hybrid compounds are often found.
[15] In addition to containing small peptides, the resulting material includes fats, metals, salts, vitamins, and many other biological compounds.
Peptides of specific shorter lengths are named using IUPAC numerical multiplier prefixes: The same words are also used to describe a group of residues in a larger polypeptide (e.g., RGD motif).