What Is a Peptide? The Simple Definition, Without Jargon
Amino acids, peptide bond, difference with a protein, natural and synthetic peptides: the basics for understanding what a research vial contains.
Contents
The word peptide is everywhere in the scientific literature, but its definition often remains vague. Here are the essentials, in simple terms.
A chain of amino acids
A peptide is a chain of amino acids linked to one another. Amino acids are small molecules, twenty of them in living organisms (glycine, alanine, histidine, lysine…). Picture them as beads of twenty different colours: the order in which they are strung is called the sequence, and it gives the peptide its identity.
The peptide bond
Two amino acids are joined by a peptide bond, formed between the acid group of one and the amine group of the next. Its description at the end of the 19th century opened the way to protein chemistry (see our article on the history of research peptides).
Peptide or protein?
The difference is mainly a matter of size:
- a peptide usually has 2 to about 50 amino acids;
- a protein has more, often hundreds, and adopts a complex three-dimensional shape.
The boundary is not strict, but the order of magnitude is enough. Small peptides have names that state their length: dipeptide (2), tripeptide (3, like GHK), tetrapeptide (4, like epitalon), and so on.
Natural peptides
The body itself produces a great many peptides: hormones (oxytocin, glucagon, GLP-1), nervous-system messengers, fragments of larger proteins. Many research peptides are copies or analogues of these natural molecules.
Synthetic peptides
In the lab, peptides are made by solid-phase synthesis: the first amino acid is attached to a support, then the next ones are added one by one. The product is then purified, analysed (purity, identity) and lyophilized (see lyophilization explained).
What does "research peptide" mean?
A research peptide is a laboratory reagent: it is intended for scientific work, *in vitro* or in experimental models, not for use in humans. Its quality is judged by its certificate of analysis (see how to read a certificate of analysis) and its compliance with the "Research Use Only" framework (see what RUO means).
To learn more
Research Use Only (RUO). This popular-science article presents chemistry concepts. It constitutes neither a recommendation for use in humans or animals nor a therapeutic claim.
