What is a peptide?
A peptide is nothing more than a short chain of amino acids. What makes it special is not its length but its order: that order decides which message the chain carries.
Beads on a string
Amino acids are the building blocks of every protein in your body. Twenty of them occur as standard. Each one has the same attachment points on either side, so they can be strung together like beads on a string. The link between two beads is called a peptide bond, and that is where the word peptide comes from.
Such a chain is not a limp thread. Once made, it folds itself into a shape that belongs to the order of its beads. That shape is the whole point: a peptide works because its shape fits exactly onto a spot elsewhere in the body, like a key in a lock.
The order is the message
Swap two amino acids in a chain and you have a different substance, with a different shape and often a completely different effect. That is why peptides are always described in the literature by their full sequence. Two peptides can be made of exactly the same twenty building blocks and still have nothing to do with one another.
The best known example in this field is GHK-Cu, a chain of three amino acids: glycine, histidine and lysine. Swap the first two and you get a substance that no longer holds the same copper ion. The chain is identical in weight and composition, but not in behaviour.
How short is short?
There is no hard line between a peptide and a protein. In practice a chain of up to about fifty amino acids is called a peptide, and anything longer a protein. The border is arbitrary but practical: up to that length you can build a chain in the lab, beyond it you usually need living cells to make it for you.
| Length | Name | Example |
|---|---|---|
| 2 to 3 | di- or tripeptide | GHK-Cu (3) |
| 4 to 20 | oligopeptide | Epithalon (4), oxytocin (9), BPC-157 (15) |
| 20 to 50 | polypeptide | Sermorelin (29), VIP (28) |
| 50 and up | protein | Growth hormone (191) |
What do peptides do in the body?
Almost everything the body has to pass from one place to another travels through messenger substances. Peptides are a large group of those. Insulin is a peptide. Oxytocin is a peptide. The hormones your gut releases after a meal are peptides. They work by docking onto a receptor: a protein on the outside of a cell that responds to a particular shape.
As soon as a peptide fits its receptor, that receptor passes a signal to the inside of the cell. The cell then does something different from before. That is the whole mechanism, and it explains why a very small amount of substance can have a large effect: the peptide does not do the work itself, it only presses a button.
Your stomach is built to break proteins down into loose amino acids. A peptide you swallow gets cut into pieces before it arrives anywhere. That is the main reason peptides in research are almost never given by mouth, and why a lot of research is about ways to keep a chain intact for longer.
Why there are so many variants
A natural peptide is often broken down within minutes. For the body that is useful, because a message has to be able to stop as well. For research it is awkward, because you want to be able to follow what happens.
So modified versions of many natural peptides have been made. Sometimes an amino acid is replaced by a variant that enzymes do not recognise. Sometimes a fatty acid tail is attached, so the chain clamps onto a protein in the blood instead of disappearing through the kidneys. Sometimes a layer of PEG is wrapped around it. The aim is always the same: to make the message last longer than nature intended.
In short
- A peptide is a short chain of amino acids, usually up to about fifty.
- The order of those amino acids sets the shape, and the shape sets what it does.
- Peptides act as messengers: they fit a receptor and set something in motion there.
- They are broken down quickly, and much research is about ways to slow that down.
This site is made by the team behind Apex Bio Research, a Dutch supplier of research peptides with a certificate of analysis per batch.
Visit the shopThis site explains what the scientific literature says about peptides. It is not medical advice and not a set of instructions. The substances discussed here are research compounds: they are not approved for use in humans or animals. If you have a health question, see a doctor.
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