A peptide is a short chain of amino acids joined end to end. Amino acids are the small molecules that all proteins are built from, and the link between two of them is called a peptide bond. When the chain is short, it is called a peptide. When it is long and folded into a stable shape, it is called a protein.
There is no hard line between the two. As a rule of thumb, chains of roughly two to fifty amino acids are called peptides, and longer chains are called proteins.
What peptides do in the body
The body makes thousands of different peptides, and most of them work as messengers.
- Signalling. Many hormones are peptides. They are released by one tissue, travel through the blood and deliver an instruction to another tissue.
- Communication in the brain. Nerve cells release peptides that adjust mood, appetite, sleep and the response to stress.
- Defence. Skin and immune cells produce peptides that help protect against microbes.
- Repair. Fragments released when tissue is damaged act as signals that start the rebuilding process.
Why the sequence matters
There are twenty standard amino acids, and a peptide is defined by which ones it contains and the exact order they come in. Changing a single position can change what the peptide binds to and therefore what it does. This is why two peptides of the same length can have completely different roles.
Where peptides come from
- Made by the body. Cells assemble peptides from amino acids following instructions in their genes, or cut them out of larger proteins.
- From food. Digestion breaks dietary protein down into single amino acids and very short peptides, which are absorbed and reused.
- Made in a laboratory. Chemists can build a peptide by adding one amino acid at a time in a set order. The standard method, solid-phase synthesis, earned its inventor a Nobel Prize in 1984.
How peptides are studied
Because a peptide is defined by its sequence, laboratories confirm two things about any sample: that it is the right molecule, and how pure it is. Identity is usually checked by measuring the mass of the molecule, and purity by separating the sample into its components and measuring each one.
This article is for general educational purposes only and is not medical advice.
Frequently asked questions
What is a peptide?
A short chain of amino acids joined by peptide bonds.
What is the difference between a peptide and a protein?
Mainly size. Chains of up to about fifty amino acids are usually called peptides, and longer, folded chains are called proteins.
Does the body make its own peptides?
Yes. The body makes thousands of them, and many act as hormones or other chemical messengers.
Why does the order of amino acids matter?
The sequence determines the shape of the peptide and what it can bind to, which determines what it does.
Are peptides found in food?
Dietary protein is broken down into amino acids and very short peptides during digestion.
Is this medical advice?
No. This article is general educational information only.