AskDefine | Define polypeptide

Dictionary Definition

polypeptide n : a peptide containing 10 to more than 100 amino acids

User Contributed Dictionary

English

Noun

  1. A small protein containing up to 100 amino acids.

Translations

a small protein containing up to 100 amino acids
  • Italian: polipeptide

Extensive Definition

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.

Conventions

One 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 Native chemical ligation has given access to even longer proteins, so this convention seems to be outdated.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 classes

Here 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 biology

Peptides 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 humans

The 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.

Opioid peptides

Calcitonin peptides

Notes on terminology

See also

References

polypeptide in Arabic: هضميد
polypeptide in Bulgarian: Полипептид
polypeptide in Catalan: Pèptid
polypeptide in Czech: Peptid
polypeptide in Danish: Peptid
polypeptide in German: Peptid
polypeptide in Estonian: Peptiidid
polypeptide in Spanish: Péptido
polypeptide in Esperanto: Peptido
polypeptide in Persian: پپتید
polypeptide in French: Peptide
polypeptide in Korean: 펩타이드
polypeptide in Italian: Peptide
polypeptide in Hebrew: פפטיד
polypeptide in Lithuanian: Polipeptidas
polypeptide in Macedonian: Пептид
polypeptide in Japanese: ペプチド
polypeptide in Norwegian: Peptid
polypeptide in Norwegian Nynorsk: Peptid
polypeptide in Occitan (post 1500): Peptid
polypeptide in Polish: Peptydy
polypeptide in Portuguese: Peptídeo
polypeptide in Russian: Пептиды
polypeptide in Slovak: Peptid
polypeptide in Finnish: Peptidi
polypeptide in Swedish: Peptid
polypeptide in Ukrainian: Пептиди
polypeptide in Urdu: Peptide
polypeptide in Chinese: 肽
polypeptide in Turkish: peptit
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