- Plural of peptide
Peptides (from the Greek πεπτίδια, "small digestibles") are short polymers formed from the linking, in a defined order, of α-amino acids. The link between one amino acid residue and the next is known as an amide bond or a peptide bond.
Proteins are polypeptide molecules (or consist of multiple polypeptide subunits). The distinction is that peptides are short and polypeptides/proteins are long. There are several different conventions to determine these, all of which have caveats and nuances.
ConventionsOne convention is that those peptide chains that are short enough to be made synthetically from the constituent amino acids are called peptides rather than proteins. However, with the advent of better synthetic techniques, peptides as long as hundreds of amino acids can be made, including full proteins like ubiquitin. Native chemical ligation has given access to even longer proteins, so this convention seems to be outdated.
Another convention places an informal dividing line at approximately 50 amino acids in length (some people claim shorter lengths). However, this definition is somewhat arbitrary. Long peptides, such as the amyloid beta peptide linked to Alzheimer's disease, can be considered proteins; and small proteins, such as insulin, can be considered peptides.
Peptide classesHere are the major classes of peptides, according to how they are produced:
- See also Tryptone
- Are derived from animal milk or meat digested by proteolytic digestion. In addition to containing small peptides, the resulting spray-dried material includes fats, metals, salts, vitamins and many other biological compounds. Peptone is used in nutrient media for growing bacteria and fungi.
Peptides in molecular biologyPeptides have received prominence in molecular biology in recent times for several reasons. The first and most important is that peptides allow the creation of peptide antibodies in animals without the need to purify the protein of interest. This involves synthesizing antigenic peptides of sections of the protein of interest. These will then be used to make antibodies in a rabbit or mouse against the protein.
Another reason is that peptides have become instrumental in mass spectrometry, allowing the identification of proteins of interest based on peptide masses and sequence. In this case the peptides are most often generated by in-gel digestion after electrophoretic separation of the proteins.
Peptides have recently been used in the study of protein structure and function. For example, synthetic peptides can be used as probes to see where protein-peptide interactions occur.
Inhibitory peptides are also used in clinical research to examine the effects of peptides on the inhibition of cancer proteins and other diseases.
Well-known peptide families in humansThe peptide families in this section are all ribosomal peptides, usually with hormonal activity. All of these peptides are synthesized by cells as longer "propeptides" or "proproteins" and truncated prior to exiting the cell. They are released into the bloodstream where they perform their signalling functions.
Vasoactive intestinal peptides
Pancreatic polypeptide-related peptides
Notes on terminology
- A polypeptide is a single linear chain of amino acids.
- A protein is one or more polypeptides more than about 50 amino acids long.
- An oligopeptide or (simply) a peptide is a polypeptide less than 30-50 amino acids long.
- A dipeptide has two amino acids.
- A tripeptide has three amino acids.
- A pentapeptide has five amino acids.
- A nonapeptide has nine amino acids (e.g., oxytocin).
- A decapeptide has ten amino acids (e.g., gonadotrophin geleasing hormone).
- A neuropeptide is a peptide that is active in association with neural tissue.
- A peptide hormone is a peptide that acts as a hormone.
peptides in Arabic: هضميد
peptides in Bulgarian: Полипептид
peptides in Catalan: Pèptid
peptides in Czech: Peptid
peptides in Danish: Peptid
peptides in German: Peptid
peptides in Estonian: Peptiidid
peptides in Spanish: Péptido
peptides in Esperanto: Peptido
peptides in Persian: پپتید
peptides in French: Peptide
peptides in Korean: 펩타이드
peptides in Italian: Peptide
peptides in Hebrew: פפטיד
peptides in Lithuanian: Polipeptidas
peptides in Macedonian: Пептид
peptides in Japanese: ペプチド
peptides in Norwegian: Peptid
peptides in Norwegian Nynorsk: Peptid
peptides in Occitan (post 1500): Peptid
peptides in Polish: Peptydy
peptides in Portuguese: Peptídeo
peptides in Russian: Пептиды
peptides in Slovak: Peptid
peptides in Finnish: Peptidi
peptides in Swedish: Peptid
peptides in Ukrainian: Пептиди
peptides in Urdu: Peptide
peptides in Chinese: 肽
peptides in Turkish: peptit