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Sable Peptides

Peptide Bonds, Sequences and Structure: The Basics

Peptide Bonds, Sequences and Structure: The Basics is supplied for laboratory research only. Key facts are below; stored as lyophilised powder.

Last verified 12 Oct 2026.

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The short answer

Amino acids join through peptide (amide) bonds to form a chain read from the N-terminus to the C-terminus. The planar geometry of each bond, together with the side chains, decides what shapes a chain can adopt.

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The short answer

Amino acids join through peptide (amide) bonds to form a chain read from the N-terminus to the C-terminus. The planar geometry of each bond, together with the side chains, decides what shapes a chain can adopt.

The bond itself

Condensing a carboxyl group with an amino group releases water and forms an amide. Resonance gives the C–N bond partial double-bond character, so the six atoms around it lie in a plane. This is the constraint Pauling, Corey and Branson used to predict the α-helix (Pauling et al., 1951).

Reading a sequence

- `H-` or a free amine marks the N-terminus; `-OH` marks a free acid and `-NH2` an amidated C-terminus. - `Ac-` means N-acetylated. `D-` marks a D-amino acid. Cyclic or disulfide-bridged peptides are noted explicitly. - Each modification changes the molecular mass. That is why the expected mass on a COA must match the exact written sequence.

From sequence to structure

Rotation around the bonds either side of each peptide plane gives the chain its flexibility. Longer chains can form helices and sheets. Anfinsen showed that a protein's amino-acid sequence encodes its folded structure (Anfinsen, 1973). Most short research peptides, by contrast, are flexible in solution.

Why this matters in the lab

Sequence features predict solubility, the HPLC retention order, and weak points such as Asn–Gly and Met. These are covered in the solubility and stability guides.

- /learn/peptides-vs-proteins-and-amino-acids - /learn/what-are-research-peptides - /glossary

Sources

1. Pauling L et al.. The structure of proteins; two hydrogen-bonded helical configurations of the polypeptide chain. *Proc Natl Acad Sci U S A* 1951;37:205-11. PMID 14816373. PMC1063337. doi:10.1073/pnas.37.4.205 2. Anfinsen CB. Principles that govern the folding of protein chains. *Science* 1973;181:223-30. PMID 4124164. doi:10.1126/science.181.4096.223 3. Muttenthaler M et al.. Trends in peptide drug discovery. *Nat Rev Drug Discov* 2021;20:309-325. PMID 33536635. doi:10.1038/s41573-020-00135-8

*Last reviewed: 2026-10-10. Original Sable content; sources verified via PubMed E-utilities / Crossref / live HTTP checks on 2026-10-10.*

Last reviewed: 2026-10-10

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Frequently asked questions

What is a peptide bond?

An amide bond formed between the carboxyl group of one amino acid and the amino group of the next, with loss of water.

Why is the peptide bond planar?

Partial double-bond character from resonance keeps the C–N bond planar, usually in the trans configuration.

How are sequences written?

From the N-terminus to the C-terminus, using three-letter (Gly-His-Lys) or one-letter (GHK) codes.

What do modifications like 'amide' or 'acetyl' mean?

A C-terminal amide (-NH2) or N-terminal acetyl group caps the chain ends. These change charge and mass and are noted in the name.

Do short peptides fold?

Most short peptides are flexible in water. Longer chains can adopt helices and sheets, and proteins fold into defined 3-D structures.