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Peptides (from
Greek language Greek (modern , romanized: ''Elliniká'', ancient , ''Hellēnikḗ'') is an independent branch of the Indo-European family of languages, native to Greece, Cyprus, Albania, other parts of the Eastern Mediterranean and the Black Sea. It has the lo ...
πεπτός, ''peptós'' "digested"; derived from πέσσειν, ''péssein'' "to digest") are short chains of between two and fifty
amino acid Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), a ...
s, linked by
peptide bond A peptide bond is an amide type of covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide or protein chain. It can also be called ...

peptide bond
s. Chains of fewer than ten or fifteen amino acids are called
oligopeptide 300px, A tetrapeptide (example Val-Gly-Ser-Ala) with green marked amino end (L-valine) and blue marked carboxyl end (L-alanine) An oligopeptide, often just called peptide (''oligo-'', "a few"), consists of two to twenty amino acids and can include di ...
s, and include
dipeptideA dipeptide is an organic compound derived from two amino acids. The constituent amino acids can be the same or different. When different, two isomers of the dipeptide are possible, depending on the sequence. Several dipeptides are physiologically ...
s,
tripeptide A tripeptide is a peptide derived from three amino acids joined by two or sometimes three peptide bonds. As for proteins, the function of peptides is determined by the consistuent amino acids and their sequence. The simplest tripeptide is glycylgly ...
s, and
tetrapeptide A tetrapeptide is a peptide, classified as an oligopeptide, since it only consists of four amino acids joined by peptide bonds. Many tetrapeptides are pharmacologically active, often showing affinity and specificity for a variety of receptors in pro ...
s. A polypeptide is a longer, continuous, unbranched peptide chain of up to approximately fifty amino acids. Hence, peptides fall under the broad chemical classes of biological polymers and
oligomer In chemistry and biochemistry, an oligomer () is a molecule that consists of a few similar or identical repeating units which could be derived, actually or conceptually, from copies of a smaller molecule, its monomer. Quote: ''Oligomer molecule: A m ...
s, alongside
nucleic acid#REDIRECT Nucleic acid#REDIRECT Nucleic acid {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
s,
oligosaccharide An oligosaccharide (/ˌɑlɪgoʊˈsækəˌɹaɪd/; from the Greek ὀλίγος ''olígos'', "a few", and σάκχαρ ''sácchar'', "sugar") is a saccharide polymer containing a small number (typically three to ten) of monosaccharides (simple sugar ...
s,
polysaccharide , a beta-glucan polysaccharide Image:amylose 3Dprojection.svg">350px, Amylose is a linear polymer of glucose mainly linked with α(1→4) bonds. It can be made of several thousands of glucose units. It is one of the two components of starch, th ...
s, and others. A polypeptide that contains more than approximately fifty amino acids is known as a
protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
. Proteins consist of one or more polypeptides arranged in a biologically functional way, often bound to
ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron ...
s such as
coenzyme A cofactor is a non-protein chemical compound or metallic ion that is required for an enzyme's activity as a catalyst (a catalyst is a substance that increases the rate of a chemical reaction). Cofactors can be considered "helper molecules" that a ...
s and cofactors, or to another protein or other
macromolecule macromolecule A macromolecule is a very large molecule, such as a protein. They are composed of thousands of covalently bonded atoms. Many macromolecules are the polymerization of smaller molecules called monomers. The most common macromolecule ...
such as
DNA The structure of part of a DNA double helix Deoxyribonucleic acid (; DNA) is a molecule composed of two polynucleotide chains that coil around each other to form a double helix carrying genetic instructions for the development, functioning, g ...
or
RNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid (DNA) are nucleic acids. Along with lipids, proteins, and carbohydrates ...

RNA
, or to complex
macromolecular assemblies '' X-ray crystallographic model of 29 of the 33 native components, from the laboratory of Thomas Steitz. Of the 31 component proteins, 27 are shown (blue), along with its 2 RNA strands (orange/yellow). Scale: assembly is approx. 24 nm across. The t ...
. Amino acids that have been incorporated into peptides are termed Residue (chemistry)#Biochemistry, residues. A water molecule is released during formation of each amide bond. All peptides except cyclic peptides have an N-terminus, N-terminal (amine group) and C-terminus, C-terminal (carboxyl group) residue at the end of the peptide (as shown for the tetrapeptide in the image).


Classes

Many kinds of peptides are known. They have been classified or categorized according to their sources and functions. According to the Handbook of Biologically Active Peptides, some groups of peptides include plant peptides, bacterial/Antimicrobial peptides, antibiotic peptides, fungal peptides, invertebrate peptides, amphibian/skin peptides, venom peptides, cancer/anticancer peptides, vaccine peptides, immune/inflammatory peptides, brain peptides, peptide hormones, endocrine peptides, ingestive peptides, gastrointestinal peptides, cardiovascular peptides, renal peptides, respiratory peptides, opiate peptides, neurotrophic peptides, and blood–brain peptides. Some ribosomal peptides are subject to proteolysis. These function, typically in higher organisms, as hormones and signaling molecules. Some organisms produce peptides as antibiotics, such as microcins and bacteriocins. Peptides frequently have post-translational modifications such as phosphorylation, hydroxylation, sulfonation, palmitoylation, glycosylation, and disulfide bridge, disulfide formation. In general, peptides are linear, although splicing (genetics), lariat structures have been observed. More exotic manipulations do occur, such as racemization of L-amino acids to D-amino acids in platypus venom. Nonribosomal peptides are assembled by enzymes, not the ribosome. A common non-ribosomal peptide is glutathione, a component of the antioxidant defenses of most aerobic organisms. Other nonribosomal peptides are most common in unicellular organisms, plants, and fungi and are synthesized by Modularity (biology), modular enzyme complexes called ''nonribosomal peptide synthetases''. 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. These peptides are often Cyclic compound, 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. are derived from animal milk or meat digested by proteolysis. In addition to containing small peptides, the resulting material includes fats, metals, salts, vitamins, and many other biological compounds. Peptones are used in nutrient media for growing bacteria and fungi. Peptide fragments refer to fragments of proteins that are used to identify or quantify the source protein. Often these are the products of enzymatic degradation performed in the laboratory on a controlled sample, but can also be forensic or paleontological samples that have been degraded by natural effects.


Chemical synthesis

Image:Peptide Synthesis.svg, centre, upright=3.0, alt=Table of amino acids, Solid-phase peptide synthesis on a rink amide resin using Fmoc-α-amine-protected
amino acid Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), a ...


Example families

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.


Antimicrobial peptides

* Magainin family * Cecropin family * Cathelicidin family * Defensin family


Tachykinin peptides

* Substance P * Kassinin * Neurokinin A * Eledoisin * Neurokinin B


Vasoactive intestinal peptides

* Vasoactive intestinal peptide, VIP (''Vasoactive Intestinal Peptide''; PHM27) * Pituitary adenylate cyclase activating peptide, PACAP ''Pituitary Adenylate Cyclase Activating Peptide'' * Peptide PHI 27 (''Peptide Histidine Isoleucine 27'') * Growth hormone releasing hormone, GHRH 1-24 ''(Growth Hormone Releasing Hormone 1-24)'' * Glucagon * Secretin


Pancreatic polypeptide-related peptides

* NPY ''(NeuroPeptide Y) * Peptide YY, PYY ''(Peptide YY)'' * APP ''(Avian Pancreatic Polypeptide)'' * Pancreatic polypeptide, PPY ''Pancreatic PolYpeptide''


Opioid peptides

* Proopiomelanocortin (POMC) peptides * Enkephalin pentapeptides * Prodynorphin peptides


Calcitonin peptides

* Calcitonin * Amylin * AGG01


Self-Assembling peptides

* Aromatic short peptides * Biomimetic peptides * Peptide amphiphiles *Peptide dendrimers


Other peptides

* Ventricular natriuretic peptide, B-type Natriuretic Peptide (BNP) - produced in the myocardium and useful in medical diagnosis * Lactotripeptides - Lactotripeptides might reduce blood pressure, although the evidence is mixed. * Peptidic components from traditional Chinese medicine Colla Corii Asini in hematopoiesis.


Terminology


Length

Several terms related to peptides have no strict length definitions, and there is often overlap in their usage. *A ''polypeptide'' is a single linear chain of many amino acids (any length), held together by amide bonds. *A ''
protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
'' consists of one or more polypeptides (more than about 50 amino acids long). *An ''
oligopeptide 300px, A tetrapeptide (example Val-Gly-Ser-Ala) with green marked amino end (L-valine) and blue marked carboxyl end (L-alanine) An oligopeptide, often just called peptide (''oligo-'', "a few"), consists of two to twenty amino acids and can include di ...
'' consists of only a few amino acids (between two and twenty).


Number of amino acids

Peptides of defined length are named using IUPAC numerical multiplier prefixes. *A ''Wikt:Monopeptide, monopeptide'' has one amino acid. *A ''
dipeptideA dipeptide is an organic compound derived from two amino acids. The constituent amino acids can be the same or different. When different, two isomers of the dipeptide are possible, depending on the sequence. Several dipeptides are physiologically ...
'' has two amino acids. *A ''
tripeptide A tripeptide is a peptide derived from three amino acids joined by two or sometimes three peptide bonds. As for proteins, the function of peptides is determined by the consistuent amino acids and their sequence. The simplest tripeptide is glycylgly ...
'' has three amino acids. *A ''
tetrapeptide A tetrapeptide is a peptide, classified as an oligopeptide, since it only consists of four amino acids joined by peptide bonds. Many tetrapeptides are pharmacologically active, often showing affinity and specificity for a variety of receptors in pro ...
'' has four amino acids. *A ''pentapeptide'' has five amino acids. *A ''hexapeptide'' has six amino acids. *A ''heptapeptide'' has seven amino acids. *An ''octapeptide'' has eight amino acids (''e.g.'', Angiotensin#Angiotensin II, angiotensin II). *A ''nonapeptide'' has nine amino acids (''e.g.'', oxytocin). *A ''decapeptide'' has ten amino acids (''e.g.'', gonadotropin-releasing hormone and angiotensin#Angiotensin I, angiotensin I).


Function

*A ''neuropeptide'' is a peptide that is active in association with neural tissue. *A ''lipopeptide'' is a peptide that has a lipid connected to it, and ''pepducins'' are lipopeptides that interact with GPCRs. *A ''peptide hormone'' is a peptide that acts as a hormone. *A proteose is a mixture of peptides produced by the hydrolysis of proteins. The term is somewhat archaic. *A peptidergic agent (or drug) is a chemical which functions to directly modulate the peptide systems in the body or brain. An example is opioidergics, which are neuropeptidergics. *Cell-penetrating peptide is a peptide able to penetrate the cell membrane.


See also

*Acetyl hexapeptide-3 * Beefy meaty peptide *Collagen hybridizing peptide, a short peptide that can bind to denatured collagen in tissues * Bis-peptide * CLE peptide * Epidermal growth factor * ''Journal of Peptide Science'' * Lactotripeptides * Micropeptide * Multifunctional peptide * Neuropeptide * Palmitoyl pentapeptide-4 * Pancreatic hormone * peptide spectral library * Peptide synthesis * Peptidomimetics (such as peptoids and beta-peptide, β-peptides) to peptides, but with different properties. * Protein tag, describing addition of peptide sequences to enable protein isolation or detection * Replikins * Ribosome * Translation (biology)


References

{{Authority control Peptides, Peptides