What Are Peptides?

A peptide is a short chain of amino acids joined by peptide bonds. Amino acids are the same building blocks that make up proteins — the difference between a peptide and a protein is essentially one of length and structural complexity.

Conventionally, chains of roughly two to fifty amino acids are described as peptides, while longer chains that fold into stable three-dimensional structures are described as proteins. The boundary is a convention of usage rather than a hard biological rule.

The body already uses peptides as signalling molecules. Insulin, glucagon, oxytocin and growth hormone releasing hormone are all peptides. Because these molecules bind specific receptors, they tend to produce targeted effects rather than broad systemic ones.

That specificity is what makes synthetic peptides attractive to researchers. A peptide designed around a natural sequence can be studied for its interaction with a known receptor, and modifications to the sequence can extend how long it survives in circulation.

Most research peptides are produced by solid-phase peptide synthesis, a method in which amino acids are added one at a time to a growing chain anchored to a resin bead. The finished chain is cleaved from the resin, purified — usually by high-performance liquid chromatography — and then freeze-dried.

Freeze-drying, or lyophilisation, is why research peptides arrive as a small amount of white powder in a sealed vial. Removing water dramatically extends how long the material stays stable.

A peptide is not automatically safe because it is 'natural'. Sequence, dose, purity and delivery route all determine what a compound does in a biological system.

Most compounds catalogued in databases like this one are research chemicals. That means they have been characterised in laboratory and sometimes clinical settings, but the majority have not been approved as medicines.