Peptide
From Wikipedia, the free encyclopedia
"Peptides" redirects here. For the journal, see Peptides (journal).
A tetrapeptide (example Val-Gly-Ser-Ala) with green marked amino end (L-Valine) and blue marked carboxyl end (L-Alanine).
Peptides (from Gr. πεπτός, "digested", derived from πέσσειν, "to digest") are short chains of amino acid monomers linked by peptide (amide) bonds, the covalent chemical bonds formed when the carboxyl group of one amino acid reacts with the amino group of another. Peptides are distinguished from proteins on the basis of size, and as a benchmark can be understood to contain approximately 50 amino acids or less[citation needed]. The shortest peptides are dipeptides, consisting of 2 amino acids joined by a single peptide bond, followed by tripeptides, tetrapeptides, etc. A polypeptide is a long, continuous, and unbranched peptide chain. Hence, peptides fall under the broad chemical classes of biological oligomers and polymers, alongside nucleic acids, oligo- and polysaccharides, etc.
Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to ligands such as coenzymes and cofactors, or to another protein or other macromolecule (DNA, RNA, etc.), or to complex macromolecular assemblies. Finally, while aspects of the techniques that apply to peptides versus polypeptides and proteins differ (i.e., in the specifics of electrophoresis, chromatography, etc.), the size boundaries that distinguish peptides from polypeptides and proteins are not hard and fast: long peptides such as amyloid beta have been referred to as proteins, and smaller proteins like insulin have been considered peptides.
Amino acids that have been incorporated into peptides are termed "residues"; all peptides except cyclic peptides have an N-terminal and C-terminal residue at the end of the peptide (as shown for the tetrapeptide in the image).
http://en.wikipedia.org/wiki/Peptide
留言列表
