What Are
Peptides?
A peptide is a short chain of amino acids linked by peptide bonds. Peptides sit between individual amino acids and larger proteins on a spectrum of size. Research peptides are typically synthetic and supplied lyophilised as reference materials.
Amino acids and the peptide bond
Peptides are built from amino acids — small molecules that are the building blocks of proteins. There are twenty standard amino acids, and the order in which they are strung together defines a given peptide.
Amino acids join through a peptide bond: a chemical link formed between the carboxyl group of one amino acid and the amino group of the next, releasing a molecule of water. A chain of amino acids joined this way has two ends — the N-terminus (free amino group) and the C-terminus (free carboxyl group) — and peptides are conventionally written and read from N to C.
Peptides versus proteins
The difference between a peptide and a protein is essentially one of size, and the boundary is not sharp. Short chains are called peptides; longer chains that fold into defined three-dimensional structures are called proteins. As a rough convention, chains up to a few dozen residues are described as peptides, while larger molecules are proteins. Terms like oligopeptide (a few residues) and polypeptide (many) mark points along the same spectrum.
How peptide sequences are described
A peptide's sequence is usually written using one-letter or three-letter codes for its amino acids — for example the sequence GEPPPGKPADDAGLV describes a specific fifteen-residue peptide. The length is often reflected in the name: a nonapeptide has nine residues, a pentadecapeptide fifteen.
This is why the research literature can identify a peptide precisely: the sequence is an exact specification, and analytical methods such as mass spectrometry can confirm a sample matches it.
What a research peptide is
The peptides supplied for research are typically synthetic — assembled in the laboratory rather than extracted from a natural source — and supplied lyophilised as reference materials. How they are built is covered in how research peptides are made. They are supplied strictly for laboratory research use and are not medicinal products.
Frequently Asked Questions
A peptide is a short chain of amino acids linked together by peptide bonds. Peptides sit between individual amino acids and larger proteins on a spectrum of size.
The difference is essentially size, and the boundary is not sharp. Short amino acid chains are called peptides; longer chains that fold into defined structures are called proteins. As a rough convention, chains up to a few dozen residues are peptides.
A peptide bond is the chemical link between two amino acids, formed between the carboxyl group of one and the amino group of the next, releasing a molecule of water. It is what joins amino acids into a chain.