Intermediate Topic 828 of 1102 Organic Chemistry
Peptide Bond
An amide link between the carboxyl of one amino acid and the amine of another.
In-depth explanation of Peptide Bond
A peptide bond is an amide link formed when the carboxyl group of one amino acid condenses with the amino group of another, releasing a molecule of water. The C-N bond has partial double-bond character because of resonance, so the peptide unit is planar and rigid, and the trans geometry is usually preferred. Polypeptide chains are written from the N-terminus, which carries a free amino group, to the C-terminus, which carries a free carboxyl group. The rigidity of the peptide bond strongly influences how proteins fold.
Going deeper: Peptide Bond
Key ideas: An amide bond joins the carboxyl of one amino acid to the amino group of the next with loss of water. The C-N bond has partial double character (about 132 pm), making the unit planar, nearly always trans, with restricted rotation (except with proline). Peptides are named from the N-terminus to the C-terminus, so Gly-Ala has the free amino group on glycine. A tripeptide of 3 different residues has 6 possible sequences.
Common mistakes and connections: Students count peptide bonds as the number of residues instead of one fewer. Another error is writing the sequence in the wrong direction, or forgetting water loss in each bond. Links to amide resonance, protein secondary structure (alpha helix, beta sheet), hydrolysis and enzymes.
Visualization of Peptide Bond
The amine nitrogen of one amino acid attacks the carbonyl carbon of another, and loss of water gives the planar amide (peptide) bond. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Glycine and alanine join to form the dipeptide Gly-Ala, with a peptide bond between the carboxyl of glycine and the amine of alanine.
Frequently asked questions about Peptide Bond
What is Peptide Bond?
An amide link between the carboxyl of one amino acid and the amine of another.
Is Peptide Bond a beginner, intermediate or advanced topic?
Peptide Bond is a intermediate topic in Organic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Peptide Bond?
Study these earlier topics in Organic Chemistry first: Reducing Sugars, Amino Acids, Zwitterions.
What comes after Peptide Bond?
The next topics in Organic Chemistry are Lipids and Nucleic Acid Structure.
Can I practise Peptide Bond with quizzes?
Yes. The interactive lesson includes a self-check question on Peptide Bond, and the Organic Chemistry quiz draws on every topic in this area.
Where Peptide Bond fits in Organic Chemistry
Peptide Bond is topic 100 of 148 in Organic Chemistry.