What a dipeptide is
A dipeptide is a peptide of two amino acid residues. IUPAC–IUBMB naming rules count residues with a prefix before "peptide", so di- means two; their own worked example is glycine joined to alanine, "the dipeptide formed", named glycylalanine.[1]
- One bond. The two residues are joined by one peptide (amide) bond, and one molecule of water is lost.[1] See what is a peptide bond.
- Two ends. One end keeps a free amino group (the N-terminus), the other a free carboxyl group (the C-terminus). Names and one-letter sequences are written from the N-terminus.[1]
- Not only α-amino acids. IUPAC's definition of peptides covers any amino carboxylic acids, so β-alanine dipeptides such as carnosine count.[2]
How many dipeptides are possible?
400 linear dipeptides can be built from the 20 standard amino acids, because each of the two positions can hold any of the 20.
A cell-biology textbook gives the general rule: with 20 amino acids at every position there are 20n possible chains of length n.[3] For n = 2 that is 20 × 20 = 400. The count includes pairs like Gly-Ala and Ala-Gly separately, because order changes the molecule, and it excludes β-amino acids, D-forms and modified ends.
| Dipeptide | N-terminus | C-terminus | Formula | MW (calculated) |
|---|---|---|---|---|
| Gly-Ala (glycylalanine) | Glycine | Alanine | C5H10N2O3 | 146.15 g/mol |
| Ala-Gly (alanylglycine) | Alanine | Glycine | C5H10N2O3 | 146.15 g/mol |
Formulas and weights above come from the calculator on this page, which uses IUPAC atomic weights.[7]
Dipeptide examples
Three well-known dipeptides show how varied they are: one is in muscle, one is a modified version of it, and one is a sweetener.
| Dipeptide | Made of | Formula | MW | Note |
|---|---|---|---|---|
| Carnosine[4] | β-Alanine + histidine | C9H14N4O3 | 226.23 | Uses β-alanine, a non-standard amino acid |
| Anserine[5] | β-Alanine + 3-methylhistidine | C10H16N4O3 | 240.26 | A methylated version of carnosine |
| Aspartame[6] | Aspartic acid + phenylalanine, methyl ester | C14H18N2O5 | 294.30 | A dipeptide methyl ester |
The calculator handles standard amino acids only, so it cannot model carnosine or anserine. Aspartame shows the arithmetic: Asp-Phe is C13H16N2O5 (280.28 g/mol); adding a methyl ester adds CH2 (14.03 g/mol), giving 294.30, which matches PubChem.
Dipeptide vs tripeptide vs polypeptide
The names only count residues; IUPAC's 1995 glossary calls peptides of ten or more residues polypeptides.[2]
| Name | Residues | Peptide bonds | Possible sequences (20 amino acids) |
|---|---|---|---|
| Dipeptide | 2 | 1 | 400 |
| Tripeptide | 3 | 2 | 8,000 |
| Tetrapeptide | 4 | 3 | 160,000 |
| Polypeptide | 10 or more | 9 or more | 20n |
The tetrapeptide count is the one the textbook works out (160,000).[3] The tripeptide page covers three-residue examples, including two on this site, GHK and KPV.
Related pages
- What is a peptide bond?How the link forms and breaks
- TripeptideGlutathione, GHK, KPV and TRH
- What are peptides?Sizes, uses and the 40-amino-acid line
Frequently asked questions
What is a dipeptide?
Two amino acids joined by one peptide bond. One molecule of water is lost when the bond forms.[1]
How many dipeptides can be made from 20 amino acids?
400 (20 × 20), counting each order separately, following the 20n rule for chains of length n.[3]
What are examples of dipeptides?
How do you calculate the molecular weight of a dipeptide?
Add the molecular weights of the two amino acids and subtract one water (18.02 g/mol). The calculator on this page does it from the one-letter sequence.
Sources
- IUPAC-IUB JCBN: Nomenclature and symbolism for amino acids and peptides, 3AA-11 to 3AA-13 (peptides, residues, peptide bonds)
- IUPAC glossary of class names (1995): peptides, polypeptides, proteins
- Alberts B et al. Molecular Biology of the Cell, 4th ed., chapter 3: The shape and structure of proteins
- PubChem CID 439224: carnosine
- PubChem CID 112072: anserine
- PubChem CID 134601: aspartame
- Abridged standard atomic weights 2024