Foundations

What are peptides?

A peptide is a short chain of amino acids. That single sentence carries most of the science — provided the terms in it are used exactly.

Published 2026-01-12 · Reading time 7 min

The definition, stated exactly

A peptide is a chain of amino acids linked by peptide bonds. By convention the term applies up to roughly fifty residues; above that length the molecule is called a protein. The boundary is a convention of nomenclature, not a change in chemistry.

What matters biologically is the sequence: the exact order of amino acids determines the conformation the chain adopts, and conformation determines which molecular structures the peptide can recognise. Two peptides of identical length and composition but different order are different molecules with different behaviour.

How a peptide acts

Many peptides function as signalling molecules. The general description runs in five steps: molecule, molecular target, cellular signal, biological process, measurable outcome. A peptide recognises a target — most often a receptor — binding alters the activity of the cell, and under defined conditions that change can be observed and measured.

Two properties determine how informative any such observation is. Affinity describes how strongly the molecule binds its target. Selectivity describes how many distinct targets it binds. High affinity with poor selectivity produces effects that are difficult to attribute to a single pathway.

Stability is a research constraint

Peptides are degraded by peptidases. Half-life is therefore usually short, which constrains study design and the interpretation of results: a brief window of exposure limits what can be attributed to the molecule and what belongs to downstream processes.

Lyophilisation — vacuum freeze-drying — addresses the storage side of the same problem. Removing water slows hydrolytic and enzymatic degradation, which is why reference material is supplied as a solid powder rather than a solution.

Reading the evidence

Not all published information carries the same weight. A result obtained in cell culture is not equivalent to a result in an animal model, and neither is equivalent to a controlled clinical trial in humans.

Every reference entry in this library states the type of research it rests on, the assigned evidence level and what remains uncertain. Claims taken from non-peer-reviewed literature are presented as source claims, not as scientific consensus. This separation between what has been studied and what has been demonstrated is deliberate.

Referenced compounds

BPC-157

TB-500

Semax

GHK-Cu (Copper Peptide)

Further reading

Peptide reference library Evidence framework Scientific glossary

Disclaimer

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