Peptide Bond
The amide linkage that joins amino acids, how it forms, and why its planar geometry shapes peptide handling and stability.
Published 14 Sept 2026 · Updated 14 Sept 2026
A dehydration reaction
A peptide bond forms when the carboxyl group of one amino acid reacts with the amino group of another, releasing water. The result is an amide linkage between the carbonyl carbon of one residue and the nitrogen of the next. This single reaction repeated along a chain is what builds the peptide backbone.
Planar and partially double-bonded
The amide bond is not a freely rotating single bond. Electron delocalisation between the carbonyl and the nitrogen gives it partial double-bond character, making the linkage planar and restricting rotation. Most peptide bonds adopt the trans configuration, in which adjacent side chains sit on opposite sides of the bond. This constraint is part of why peptide conformation is predictable rather than random, and it underpins secondary structure in longer chains.
Directionality
Because synthesis proceeds from one end to the other, a peptide has two chemically distinct termini: an N-terminus carrying the free amine, and a C-terminus carrying the carboxyl group. Modifications are described by referring to one of these ends, so knowing which end is which is essential when specifying acetylation, amidation, or conjugation.
Stability
Peptide bonds are stable under ordinary handling conditions but can be cleaved by hydrolysis, particularly under strongly acidic or basic conditions, at elevated temperature, or through enzymatic action. This is the practical reason handling guidance emphasises pH control, temperature control, and cleanliness of the vessels and solvents used.