This article will be permanently flagged as inappropriate and made unaccessible to everyone. Are you certain this article is inappropriate? Excessive Violence Sexual Content Political / Social
Email Address:
Article Id: WHEBN0000024029 Reproduction Date:
Peptides (from Gr. πεπτός, "digested", derived from πέσσειν, "to digest") are naturally occurring biological molecules. They are short chains of amino acid monomers linked by peptide (amide) bonds. The covalent chemical bonds are formed when the carboxyl group of one amino acid reacts with the amino group of another. 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.
Peptides are distinguished from proteins on the basis of size, and as an arbitrary benchmark can be understood to contain approximately 50 or fewer amino acids.[1] 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 absolute: 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" due to the release of either a hydrogen ion from the amine end or a hydroxyl ion from the carboxyl end, or both, as a water molecule is released during formation of each amide bond.[2] 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).
Peptides are divided into several classes, depending on how they are produced:
However, these peptides frequently have posttranslational modifications, such as phosphorylation, hydroxylation, sulfonation, palmitoylation, glycosylation and disulfide formation. In general, they are linear, although lariat structures have been observed.[5] More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in platypus venom.[6]
These complexes are often laid out in a similar fashion, and they can contain many different modules to perform a diverse set of chemical manipulations on the developing product.[9] These peptides are often cyclic and can have highly complex cyclic structures, although linear nonribosomal peptides are also common. Since the system is closely related to the machinery for building fatty acids and polyketides, hybrid compounds are often found. The presence of oxazoles or thiazoles often indicates that the compound was synthesized in this fashion.[10]
Peptides received prominence in molecular biology for several reasons. The first is that peptides allow the creation of peptide antibodies in animals without the need to purify the protein of interest.[16] 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- see the page on Protein tags.
Inhibitory peptides are also used in clinical research to examine the effects of peptides on the inhibition of cancer proteins and other diseases.[17] For example, one of the most promising application is through peptides that target LHRH.[18] These particular peptides act as an agonist, meaning that they bind to a cell in a way that regulates LHRH receptors. The process of inhibiting the cell receptors suggests that peptides could be beneficial in treating prostate cancer. However, additional investigations and experiments are required before the cancer-fighting attributes, exhibited by peptides, can be considered definitive.[19]
The peptide families in this section are 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 signaling functions.
Length:
Number of amino acids:
Function:
The term peptide has been incorrectly or unclearly used to mean illegal secretagogue and peptide hormones in sports doping matters: illegal secretagogue peptides are classified as Schedule 2 (S2) prohibited substances on the World Anti-Doping Agency (WADA) Prohibited List, and are therefore prohibited for use by professional athletes both in and out of competition. Such peptide secretagogues have been on the WADA prohibited substances list since at least 2008. The Australian Crime Commission (incorrectly using the term peptides) cited the alleged misuse of the following illegal peptide secretagogues used in Australian sport - and specifically by Jobe Watson from the Essendon Football Club:[24] growth hormone releasing hormones CJC-1295, GHRP-6, GHSR (gene) hexarelin. There is ongoing controversy on the legality of using peptide secretagogues in sports.[25]
: END
///
()//, /
, drug (////)
Metabolism, X-ray crystallography, Protein folding, Biochemistry, Glycolysis
Biochemistry, Amino acid, Leucine, Bromine, Mass spectrometry
GnRH Neuron, Follicle-stimulating hormone, Luteinizing hormone, Peptide, Hypothalamus
Melanocyte-stimulating hormone, Adrenocorticotropic hormone, Lipotropin, Hypothalamus, Cholecystokinin
Protein, Extraction (chemistry), Silver, Calcium, Mass spectrometry
Receptor Antagonist, Phenylalanine, Functional group, Psychology, Aprepitant
Cancer, Bacteria, Salt, Peptide, Schizophrenia
Tyrosine, Glycine, Proline, Cysteine, Lysine
Serotonin, 5-Carboxamidotryptamine, 5-Methoxytryptamine, Metitepine, Lysergic acid diethylamide