The peptide bond is the chemical link that joins amino acids into peptides and proteins. Understanding its formation and structure helps explain why peptide chains have directionality, limited flexibility at specific positions, and predictable behavior in synthesis and analysis.
At a glance
- Peptide bond = amide bond formed between the C-terminus of one amino acid and the N-terminus of another.
- Condensation reaction: Bond formation releases water.
- Partial double-bond character makes the bond more rigid than a typical single bond.
What is a peptide bond?
A peptide bond forms when the carboxyl group (C-terminus) of one amino acid reacts with the amino group (N-terminus) of another. The resulting linkage is an amide (–CO–NH–). When repeated, these amide links create the peptide backbone.
Why the peptide bond is relatively rigid
Unlike many single bonds that rotate freely, the peptide bond exhibits resonance between the carbonyl and the amide nitrogen. This delocalization gives the bond partial double-bond character, which:
- reduces rotation around the C–N bond,
- encourages a planar local geometry, and
- helps define peptide backbone conformations.
Cis vs trans (and why it matters)
Most peptide bonds prefer the trans configuration because it minimizes steric clashes. Some residues (notably proline) can increase the likelihood of cis conformations in certain contexts, which can be relevant to folding studies and conformational analysis.
Formation vs breakdown
In aqueous environments, peptide bonds can be hydrolyzed, but spontaneous hydrolysis is typically slow under mild conditions. In practical research workflows, hydrolysis becomes more relevant under harsh pH/temperature exposure or when enzymes and catalytic systems are involved.
Practical notes for researchers
- Sequence direction: Peptide sequences are written N-terminus → C-terminus.
- Backbone constraints: Limited rotation at the peptide bond influences conformational sampling.
- Analytical behavior: Backbone chemistry supports common LC/MS and chromatographic approaches.
