Peptide Bonds & Chain Formation

When two amino acids join together, they form a chemical bond called a peptide bond. This bond forms between the carboxyl group (–COOH) of one amino acid and the amino group (–NH₂) of another, releasing a water molecule in the process — a reaction known as a condensation reaction or dehydration synthesis.

A chain of two amino acids is called a dipeptide. Three amino acids form a tripeptide. Chains of up to approximately 50 amino acids are called peptides, while longer chains (50+) are classified as polypeptides or proteins.

Size Classification

Dipeptide	2 amino acids
Tripeptide	3 amino acids
Oligopeptide	4–20 amino acids
Peptide	2–50 amino acids
Polypeptide / Protein	50+ amino acids

The sequence of amino acids in a peptide chain determines its three-dimensional shape, and that shape determines its biological function. Even a small change in the sequence — swapping one amino acid for another — can completely alter what the peptide does in the body. This specificity is what makes peptides such powerful and precise biological tools.