Peptides are usually shorter than proteins, but there is no universal cut-off point used across the scientific disciplines. Oligopeptides can be short chains. A longer one might be called a polypeptide. Normally, proteins consist of one or more long polypeptides, which have a specific three-dimensional shape.
The sequence of a peptide is of great importance. It provides the exact sequence of amino acids. Usually this is written from the N terminus to the C terminus. Take, for instance, Gly-Ala-Ser and Ser-Ala-Gly. They consist of the same three amino acids arranged differently. This change in the order of amino acids can change the behaviour of the peptide or how it interacts with other molecules.
Peptides are natural products of living organisms and can be involved in signalling, regulation and other biological processes. They can also be synthesised in the laboratory by peptide synthesis. Synthetic peptides are widely used in research for the study of structure, activity, molecular interactions and other properties.
Some peptides contain chemical modifications in addition to their amino acid sequence. E.g., N-terminal acetylation and C-terminal amidation. Such changes may affect properties such as molecular weight, stability, solubility, or resistance to degradation. Thus, the name of a peptide may not provide all the information needed to describe a particular research material.
When studying or comparing peptides, such factors as sequence, molecular weight, purity, structure, solubility and stability may be considered. Mass spectrometry and chromatography are analytical methods that may be used to assist in characterising a peptide and checking its composition.
It is useful to differentiate peptides from proteins and small molecule compounds. Peptides and proteins are composed of amino acids, whereas small molecules are chemically distinct and are not merely strings of amino acids.
Basic terminology helps in peptide research to read product information, scientific papers, analytical data and Certificates of Analysis (CoAs). Sequence, modifications and claimed purity information can provide a better picture of what a given peptide sample contains.
See also Peptide Bond. · Amino Acid · Sequencer · Primary Structure · Polypeptide, Protein · Peptide Analogue · Molecular Weight · Purity of Peptide Certificate of Analysis
Research Use Only. This glossary explains terminology used in published research. It is not medical advice and does not describe any product for human or animal use.