The main types of peptides are grouped in four simple ways: by length (dipeptides, tripeptides, oligopeptides and polypeptides), by shape (linear or cyclic), by origin (natural or synthetic), and by the job they do in the body, such as hormones, neuropeptides and antimicrobial peptides. This plain-English guide explains each type of peptide with real examples, then shows where well-known research peptides fit.
What is a peptide? A quick refresher
A peptide is a short chain of amino acids, the same building blocks that make up proteins. Each amino acid is linked to the next by a peptide bond, which forms when two amino acids join and release a molecule of water. If you want the chemistry in more detail, our guide to what a peptide bond is and how it forms covers it step by step.
There are 20 standard amino acids, and they can be strung together in almost any order. That is why there are so many different peptides, and why scientists sort them into types rather than trying to learn every one.
Types of peptides by length
The most common way to classify peptides is simply by counting the amino acids in the chain. The names come from Greek prefixes: “di” means two, “tri” means three, “oligo” means a few and “poly” means many.
| Type | Number of amino acids | Example |
|---|---|---|
| Dipeptide | 2 | Carnosine |
| Tripeptide | 3 | Glutathione, GHK |
| Oligopeptide | Roughly 2 to 20 | Oxytocin (9), BPC-157 (15) |
| Polypeptide | Roughly 20 to 50 or more | Glucagon (29), insulin (51) |
| Protein | Usually more than 50, folded into a stable shape | Collagen, haemoglobin |
These cut-off points are rules of thumb, not strict laws, and different textbooks draw the lines slightly differently. We explain where peptides end and proteins begin in our peptides vs proteins comparison.
Dipeptides and tripeptides: the smallest peptides
Dipeptides and tripeptides are tiny, but some of them are surprisingly important. Carnosine, a dipeptide made from beta-alanine and histidine, is found in high amounts in muscle and brain tissue (Boldyrev and colleagues, Physiological Reviews, 2013).
Glutathione is a tripeptide made from glutamate, cysteine and glycine. It is one of the most abundant small molecules inside cells and acts as a major antioxidant (Lu, Biochimica et Biophysica Acta, 2013).
Another well-studied tripeptide is GHK (glycine-histidine-lysine), which binds copper to form the complex known as GHK-Cu. Our GHK-Cu research hub explains this copper peptide in more depth.
Oligopeptides and polypeptides
Oligopeptides are short chains of a few amino acids, while polypeptides are longer chains. Many of the peptides studied in laboratories sit in this range. BPC-157, for example, is a 15-amino-acid peptide, and you can see each residue in our breakdown of the BPC-157 amino acid sequence.
Types of peptides by shape: linear and cyclic
Most peptides are linear: a straight chain with a free start (the N-terminus) and a free end (the C-terminus). Some, however, are cyclic, meaning the chain is joined into a ring.
A ring can form when the two ends of the chain link together, or when two cysteine amino acids form a disulfide bridge. Oxytocin is a good example of the second kind: it is only nine amino acids long, but six of them sit inside a small ring.
Ring-shaped peptides tend to hold their shape better and can be harder for enzymes to break down, which is one reason they attract so much research interest. Researchers at EPFL in Switzerland reviewed how cyclic peptides have developed over the past few decades (Zorzi, Deyle and Heinis, Current Opinion in Chemical Biology, 2017).
Types of peptides by origin: natural and synthetic
Natural peptides are made by living things. Your body makes them from its own genetic instructions, and others are released when the proteins in food are digested.
Synthetic peptides are built in a laboratory, one amino acid at a time. A synthetic peptide can be an exact copy of a natural one, a fragment of a larger natural molecule, or a modified version designed for research. We look at this difference in detail in are peptides natural? Natural vs synthetic peptides explained.
Types of peptides by function
Biologists often group peptides by the job they do. Here are the main families, with examples you may have heard of.
Peptide hormones
Peptide hormones are chemical messengers released into the bloodstream. Insulin (51 amino acids) and glucagon (29 amino acids) are made in the pancreas, while oxytocin and vasopressin (9 amino acids each) are released from the pituitary gland. Growth hormone-releasing hormone (GHRH) is another peptide hormone and is the starting point for several research peptides listed below.
Neuropeptides
Neuropeptides are peptides used by nerve cells to send signals. Examples include substance P (11 amino acids) and the endorphins. They tend to act more slowly and for longer than classic small-molecule neurotransmitters.
Antimicrobial peptides
Antimicrobial peptides are part of the body’s natural defences against bacteria and other microbes. They are found in almost all living things, from insects and frogs to humans. Defensins and the human peptide LL-37 are well-known examples (Zasloff, Nature, 2002).
Signal peptides and carrier peptides
Signal peptides are short sequences at the start of a newly made protein that act like a postcode, telling the cell where to send it. Carrier peptides bind and transport other molecules; GHK binding copper is a classic example.
Where popular research peptides fit
Many of the peptides studied in UK laboratories are synthetic peptides based on natural sequences. Here is how some well-known examples fit into the types above.
| Research peptide | Type by length | What it is |
|---|---|---|
| GHK-Cu | Tripeptide | The tripeptide GHK bound to a copper ion |
| Ipamorelin | Oligopeptide (5) | A synthetic pentapeptide studied as a growth hormone secretagogue |
| BPC-157 | Oligopeptide (15) | A synthetic peptide based on a sequence from a protein found in gastric juice |
| Sermorelin | Polypeptide (29) | The first 29 amino acids of natural GHRH |
| CJC-1295 | Polypeptide (29, modified) | A modified GHRH(1-29) analogue |
| Tesamorelin | Polypeptide (44) | A full-length GHRH analogue with a small chemical addition |
| TB-500 | Synthetic peptide | A research peptide based on thymosin beta-4, a natural 43-amino-acid peptide |
Knowing the type of peptide helps researchers understand how it is made, how stable it is likely to be, and which tests are needed to confirm its identity. At Peptides UK, our research peptides are Third-Party HPLC Verified, with certificates of analysis available, and every product is supplied for laboratory research use only. They are not intended for human or veterinary use.
Types of peptides: frequently asked questions
What are the main types of peptides?
Peptides are usually grouped by length (dipeptides, tripeptides, oligopeptides and polypeptides), by shape (linear or cyclic), by origin (natural or synthetic) and by the job they do in the body, such as hormones, neuropeptides and antimicrobial peptides.
What is the difference between a dipeptide and a tripeptide?
A dipeptide is made of two amino acids joined by one peptide bond. A tripeptide is made of three amino acids joined by two peptide bonds. Carnosine is a well-known dipeptide and glutathione is a well-known tripeptide.
Is insulin a peptide?
Yes. Insulin is a peptide hormone made of 51 amino acids arranged in two chains, linked by disulfide bridges. Because of its size it sits close to the informal line between a peptide and a small protein.
Is collagen a peptide?
Collagen itself is a large protein. Collagen peptides are shorter fragments produced when collagen is broken down, so they are peptides made from a protein.
How many types of peptides are there?
There is no single official count. The body makes thousands of different peptides, and scientists have made many more in the lab. That is why peptides are grouped by length, shape, origin and function rather than listed one by one.
