What Are Peptides? A Plain-English Research Guide

A peptide is a short chain of amino acids — typically between two and around fifty residues — joined by covalent peptide bonds. Anything longer than roughly fifty amino acids is generally classified as a protein, though the cut-off is conventional rather than absolute. Every peptide has a defined sequence, a defined molecular weight and (once folded) a defined three-dimensional shape that determines how it interacts with receptors and enzymes.

Amino acids are the individual building blocks. Peptides are short assembled chains. Proteins are long, often folded chains made of one or more peptide subunits. The same twenty proteinogenic amino acids can produce billions of distinct peptide sequences — which is why peptides are such a rich target for research.

Research peptides are usually grouped by function: signalling peptides (e.g. GLP-1 analogues such as semaglutide and tirzepatide), regenerative peptides (e.g. BPC-157, TB-500), growth-hormone-related peptides (e.g. CJC-1295, Ipamorelin), cosmetic peptides (e.g. GHK-Cu), and mitochondrial peptides (e.g. SS-31, MOTS-c). Each category has its own literature and its own handling profile.

Modern research peptides are produced by solid-phase peptide synthesis (SPPS), where the chain is built one amino acid at a time on a solid resin. The crude product is then purified, most commonly by reversed-phase HPLC, and verified by mass spectrometry. Quality grade is defined by purity (HPLC %), identity (mass-spec confirmation) and peptide content.

Two vials labelled the same peptide can behave very differently if one contains truncated sequences, salt or process residues. Research-grade peptides should always ship with a lot-matched Certificate of Analysis (COA) showing HPLC purity, mass-spec identity and peptide content. Anything below 98–99% HPLC purity introduces real variability into experimental results.

If you are evaluating a specific compound, the Peptide Library lists every Regena Peptides peptide with its COA. For a deeper conceptual primer, the research-compound basics page covers handling, storage and reconstitution in more detail.