Amino acid

The molecular building block of peptides and proteins — twenty standard amino acids combine to make the protein machinery of human biology.

Why it matters

Each amino acid contains an amino group (-NH2), a carboxylic acid (-COOH), and a side chain that defines its identity (glycine’s side chain is just hydrogen; tryptophan’s is an indole ring). The body synthesises eleven of the twenty; the other nine (essential amino acids) must come from diet.

In practice

For the research peptide consumer, amino acid sequence is the structural identity of the molecule. Two peptides with the same sequence but different post-translational modifications (acetylation, amidation, cyclisation) are different products with different pharmacology.

Common confusion

“Amino acid supplement” and “peptide supplement” overlap in marketing but mean different things — free amino acids are not pharmacologically equivalent to peptides built from them.

This glossary entry is editorial content reviewed against primary sources. It is not medical advice. See our Editorial Policy.