Vesicle (biology) 32572 219448891 2008-06-15T07:50:55Z DOI bot 6652755 Citation maintenance. Initiated by [[User:Fconaway|Fconaway]]. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. {{expert-subject |Molecular and Cellular Biology}} [[Image:Liposome scheme-en.svg|thumb|250px|right|Scheme of a simple [[Vesicle (biology)|vesicle]] ([[liposome]]).]] In [[cell biology]], a '''vesicle''' is a relatively small intracellular, membrane-enclosed sac that stores or transports substances . The vesicle is separated from the [[cytosol]] by at least one [[lipid bilayer]]. If there is only one [[lipid bilayer]], they are called ''unilamellar'' vesicles; otherwise they are called ''multilamellar''. Vesicles store, [[transport]], or [[digestion|digest]] [[cell (biology)|cellular]] [[product (biology)|products]] and [[waste]]. This biomembrane enclosing the vesicle is similar to that of the [[plasma membrane]]. Because it is separated from the cytosol, the intravesicular environment can be made to be different from the cytosolic environment. Vesicles can fuse with the plasma membrane, releasing their contents outside the cell. Vesicles are a basic tool of the cell for organizing [[metabolism]], transport, [[enzyme]] storage, as well as being chemical reaction chambers. Many in the [[endoplasmic reticulum]], or are made from parts of the [[plasma membrane]]. ==Some types of vesicles== * Transport vesicles can move molecules between locations inside the cell, e.g., proteins from the rough [[Endoplasmic Reticulum|endoplasmic reticulum]] to the [[Golgi Apparatus|Golgi apparatus]]. * [[Synaptic vesicle]]s are located at [[presynaptic terminal]]s in [[neurons]] and store [[neurotransmitter]]s. * [[Lysosome]]s are membrane-bound digestive [[organelle]]s that can digest macromolecules (break them down to small compounds) that were taken in from the outside of the cell by an [[Endocytosis|endocytic vesicle]]. * [[Extracellular matrix|Matrix]] vesicles are located within the extracellular space, or matrix. Using [[electron microscopy]] but working independently, they were discovered in 1967 by H. Clarke Anderson<ref>{{cite journal |author=Anderson HC |title=Electron microscopic studies of induced cartilage development and calcification |journal=J. Cell Biol. |volume=35 |issue=1 |pages=81–101 |year=1967 |pmid=6061727| doi = 10.1083/jcb.35.1.81 <!--Retrieved from CrossRef by DOI bot-->}}</ref> and Ermanno Bonucci.<ref>{{cite journal |author=Bonucci E |title=Fine structure of early cartilage calcification |journal=J. Ultrastruct. Res. |volume=20 |issue=1 |pages=33–50 |year=1967 |pmid=4195919| doi = 10.1016/S0022-5320(67)80034-0 <!--Retrieved from CrossRef by DOI bot-->}}</ref> These cell-derived vesicles are specialized to initiate [[biomineralization]] of the matrix in a variety of tissues, including [[bone]], [[cartilage]], and [[dentin]]. During normal [[calcification]], a major influx of calcium and phosphate ions into the cells accompanies cellular apoptosis (genetically determined self-destruction) and matrix vesicle formation. Calcium-loading also leads to formation of [[phosphatidylserine]]:calcium:phosphate complexes in the plasma membrane mediated in part by a protein called [[annexins]]. Matrix vesicles bud from the plasma membrane at sites of interaction with the extracellular matrix. Thus, matrix vesicles convey to the extracellular matrix calcium, phosphate, lipids and the annexins which act to nucleate mineral formation. These processes are precisely coordinated to bring about, at the proper place and time, mineralization of the tissue's matrix. * [[Endosome|Multivesicular body]], or MVB, is a membrane-bound vesicle containing a number of smaller vesicles. ==Vesicle formation and transport== [[Image:biological_cell.svg|thumb|right|300px|Schematic showing the [[cytoplasm]], with its components (or ''organelles''), of a typical animal cell. [[Organelle]]s:<br/> (1) [[nucleolus]]<br/> (2) [[cell nucleus|nucleus]]<br/> (3) [[ribosomes]] (little dots)<br/> (4) [[vesicle (biology)|vesicle]]<br/> (5) rough [[endoplasmic reticulum]] (ER)<br/> (6) [[Golgi apparatus]]<br/> (7) [[Cytoskeleton]]<br/> (8) smooth ER<br/> (9) [[mitochondrion|mitochondria]]<br/> (10) [[vacuole]]<br/> (11) [[cytoplasm]]<br/> (12) [[lysosome]]<br/> (13) [[centriole]]s within [[centrosome]]]] Some vesicles are made when part of the membrane pinches off the endoplasmic reticulum or the Golgi complex. Others are made when an object outside of the cell is surrounded by the cell membrane. ===Capturing cargo molecules=== The assembly of a vesicle requires numerous coats to surround and bind to the proteins being transported. One family of coats are called adaptins. These bind to the coat vesicle (see below). They also trap various transmembrane receptor proteins, called cargo receptors, which in turn trap the cargo molecules. ===Vesicle coat=== The vesicle coat serves to sculpt the curvature of a donor membrane, and to select specific proteins as cargo. It selects cargo proteins by binding to [[Protein targeting|sorting signals]]. In this way the vesicle coat clusters selected membrane cargo proteins into nascent vesicle buds. There are three types of vesicle coats: [[clathrin]], [[COPI]] and [[COPII]]. Clathrin coats are found on vesicles trafficking between the [[Golgi]] and [[plasma membrane]], the Golgi and [[endosome]]s, and the plasma membrane and endosomes. COPI coated vesicles are responsible for retrograde transport from the Golgi to the ER, while COPII coated vesicles are responsible for anterograde transport from the ER to the Golgi. The [[clathrin]] coat is thought to assemble in response to regulatory [[G protein]]. A coatomer coat assembles and disassembles due to an [[ADP ribosylation factors|ARF]] protein. ===Vesicle docking=== Surface markers called [[SNARE]]s identify the vesicle's cargo, and complementary SNAREs on the target membrane act to cause fusion of the vesicle and target membrane. Such v-SNARES are hypothesised to exist on the vesicle membrane, while the complementary ones on the target membrane are known as t-SNAREs. Often SNAREs associated with vesicles or target membranes are instead classified as Qa, Qb, Qc or R SNAREs owing to further variation than simply v- or t-SNAREs. An array of different SNARE complexes can be seen in different tissues and subcellular compartments, with 36 isoforms currently identified in humans. Regulatory [[Rab (G-protein)|Rab]] proteins are thought to inspect the joining of the SNAREs. Rab protein is a regulatory GTP-binding protein, and controls the binding of these complementary SNAREs for a long enough time for the Rab protein to hydrolyse its bound GTP and lock the vesicle onto the membrane. ===Vesicle fusion=== Fusion requires the two membranes to be brought within 1.5 nm of each other. For this to occur water must be displaced from the surface of the vesicle membrane. This is energetically unfavourable, and evidence suggests that the process requires ATP, GTP and acetyl-coA, fusion is also linked to budding, which is why the term budding and fusing arises. ===Vesicles in receptor downregulation=== Membrane proteins serving as [[Receptor (biochemistry)|receptor]]s are sometimes tagged for [[downregulation]] by the attachment of [[ubiquitin]]. After arriving an [[endosome]] via the pathway described above, vesicles begin to form inside the endosome, taking with them the membrane proteins meant for degregation; When the endosome either matures to become a [[lysosome]] or is united with one, the vesicles are completely degregaded. Without this mechanism, only the extracellular part of the membrane proteins would reach the lumen of the [[lysosome]], and only this part would be degraded.<ref>{{cite journal |author=Katzmann DJ, Odorizzi G, Emr SD |title=Receptor downregulation and multivesicular-body sorting |journal=Nat. Rev. Mol. Cell Biol. |volume=3 |issue=12 |pages=893–905 |year=2002 |pmid=12461556 |doi=10.1038/nrm973 | url = http://www.colorado.edu/MCDB/odorizzilab/katzmann2002.pdf | format = pdf }}</ref> It is because of these vesicles that the endosome is sometimes known as a ''multivesicular body''. The pathway to their formation is not completely understood; unlike the other vesicles described above, the outer surface of the vesicles is not in contact with the [[cytosol]]. ==See also== *[[Endoplasmic reticulum]] *[[Golgi apparatus]] *[[Micelle]] *[[Membrane nanotube]] ==Notes== {{reflist}} ==References== * Bruce Alberts, et al (1994); Molecular Biology of the Cell; Third Edition ==External links== *[http://www.biochemweb.org/lipids_membranes.shtml Lipids, Membranes and Vesicle Trafficking - The Virtual Library of Biochemistry and Cell Biology] *[http://www.zytologie-online.net/lysosomen.php Cell Biology / Membranes and Vesicles] {{organelles}} [[Category:Organelles]] [[Category:Membrane biology]] <!-- interwiki --> [[ar:حويصل (أحياء)]] [[cs:Vezikul]] [[da:Vesikel]] [[de:Vesikel]] [[es:Vesícula]] [[eo:Veziketo]] [[fr:Vésicule (biologie)]] [[ko:소포 (세포)]] [[hr:Vezikul]] [[id:Vesikel]] [[nl:Vesikel (cel)]] [[no:Vesikkel]] [[pl:Pęcherzyk]] [[pt:Transporte de vesículas]] [[fi:Vesikkeli]] [[sv:Vesikel]] [[vi:Túi tiết]] [[tr:Vezikül]] [[uk:Везикула]] [[zh:囊泡]]