What are peptides?

Amino acids are small molecules your body uses as building blocks. Link a few of them together in a chain and you have a peptide. Link a lot of them and the chain folds up into a protein.

There's no hard cut-off, but chains of roughly 2 to 50 amino acids are usually called peptides. Your body makes thousands of them. Many act as messengers: they travel to a cell, attach to a specific spot on its surface called a receptor, and tell the cell to do something.

Insulin is a familiar example of a peptide hormone. So are several modern medicines.