Cytoskeleton - wikipedia Cytoskeleton Cell biology The animal cell Components of a typical animal cell : Nucleolus Nucleus Ribosome ( little dots ) Vesicle Rough endoplasmic reticulum Golgi apparatus ( or `` Golgi body '' ) Cytoskeleton Smooth endoplasmic reticulum Mitochondrion Vacuole Cytosol ( fluid that contains organelles, comprising the cytoplasm ) Lysosome Centrosome Cell membrane The eukaryotic cytoskeleton. Actin filaments are shown in red, and microtubules composed of beta tubulin are in green. A cytoskeleton is present in all cells of all domains of life ( archaea, bacteria, eukaryotes ). It is a complex network of interlinking filaments and tubules that extend throughout the cytoplasm, from the nucleus to the plasma membrane. The cytoskeletal systems of different organisms are composed of similar proteins. In eukaryotes, the cytoskeletal matrix is a dynamic structure composed of three main proteins, which are capable of rapid growth or disassembly dependent on the cell 's requirements at a certain period of time. The structure, function and dynamic behavior of the cytoskeleton can be very different, depending on organism and cell type. Even within one cell the cytoskeleton can change through association with other proteins and the previous history of the network. There is a multitude of functions that the cytoskeleton can perform. Primarily, it gives the cell its shape and mechanical resistance to deformation, and through association with extracellular connective tissue and other cells it stabilizes entire tissues. The cytoskeleton can also contract, thereby deforming the cell and the cell 's environment and allowing cells to migrate. Moreover, it is involved in many cell signaling pathways : in the uptake of extracellular material ( endocytosis ), segregates chromosomes during cellular division, is involved in cytokinesis ( the division of a mother cell into two daughter cells ), provides a scaffold to organize the contents of the cell in space and for intracellular transport ( for example, the movement of vesicles and organelles within the cell ) ; and can be a template for the construction of a cell wall. Furthermore, it forms specialized structures, such as flagella, cilia, lamellipodia and podosomes. A large - scale example of an action performed by the cytoskeleton is muscle contraction. During contraction of a muscle, within each muscle cell, myosin molecular motors collectively exert forces on parallel actin filaments. This action contracts the muscle cell, and through the synchronous process in many muscle cells, the entire muscle. Contents 1 History 2 Eukaryotic cytoskeleton 2.1 Microfilaments ( actin filaments ) 2.2 Intermediate filaments 2.3 Microtubules 2.4 Comparison 2.5 Septins 2.6 Spectrin 2.7 Yeast cytoskeleton 3 Prokaryotic cytoskeleton 3.1 FtsZ 3.2 MreB and ParM 3.3 Crescentin 4 Common features and differences between prokaryotes and eukaryotes 5 See also 6 References 7 External links History In 1903, Nikolai K. Koltsov proposed that the shape of cells was determined by a network of tubules that he termed the cytoskeleton. The concept of a protein mosaic that dynamically coordinated cytoplasmic biochemistry was proposed by Rudolph Peters in 1929 while the term ( cytosquelette, in French ) was first introduced by French embryologist Paul Wintrebert in 1931. When the cytoskeleton was first introduced, it was thought to be a uninteresting gel - like substance that help organelles stay in place. Eukaryotic cytoskeleton Actin cytoskeleton of mouse embryo fibroblasts, stained with phalloidin Eukaryotic cells contain three main kinds of cytoskeletal filaments : microfilaments, microtubules, and intermediate filaments. Each cytoskeletal filament type is formed by polymerization of a distinct type of protein subunit and has its own characteristic shape and intracellular distribution. Microfilaments are polymers of the protein actin and are 7 nm in diameter. Microtubules are composed of tubulin and are 25 nm in diameter. Intermediate filaments are composed of various proteins, depending on the type of cell in which they are found ; they are normally 8 - 12 nm in diameter. The cytoskeleton provides the cell with structure and shape, and by excluding macromolecules from some of the cytosol, it adds to the level of macromolecular crowding in this compartment. Cytoskeletal elements interact extensively and intimately with cellular membranes. A number of small - molecule cytoskeletal drugs have been discovered that interact with actin and microtubules. These compounds have proven useful in studying the cytoskeleton and several have clinical applications. All filaments interact with accessory proteins that regulate and link the filaments to other cell compounds and each other. The accessory proteins are essential for controlled assembly of cytoskeletal filaments in particular locations, and they include motor proteins. Microfilaments ( actin filaments ) Main article : microfilament Microfilaments are composed of linear polymers of G - actin proteins, and generate force when the growing ( plus ) end of the filament pushes against a barrier, such as the cell membrane. They also act as tracks for the movement of myosin molecules that affix to the microfilament and `` walk '' along them. Myosin motoring along F - actin filaments generates contractile forces in so - called actomyosin fibers, both in muscle as well as most non-muscle cell types. Actin structures are controlled by the Rho family of small GTP - binding proteins such as Rho itself for contractile acto - myosin filaments ( `` stress fibers '' ), Rac for lamellipodia and Cdc42 for filopodia. Intermediate filaments Microscopy of keratin filaments inside cells Main article : intermediate filament Intermediate filaments are a part of the cytoskeleton of many eukaryotic cells. These filaments, averaging 10 nanometers in diameter, are more stable ( strongly bound ) than actin filaments, and heterogeneous constituents of the cytoskeleton. Like actin filaments, they function in the maintenance of cell - shape by bearing tension ( microtubules, by contrast, resist compression but can also bear tension during mitosis and during the positioning of the centrosome ). Intermediate filaments organize the internal tridimensional structure of the cell, anchoring organelles and serving as structural components of the nuclear lamina. They also participate in some cell - cell and cell - matrix junctions. Nuclear lamina exist in all animals and all tissues. Some animals like the fruit fly do not have any cytoplasmic intermediate filaments. In those animals that express cytoplasmic intermediate filaments, these are tissue specific. Different intermediate filaments are : made of vimentins. Vimentin intermediate filaments are in general present in mesenchymal cells. made of keratin. Keratin is present in general in epithelial cells. neurofilaments of neural cells. made of lamin, giving structural support to the nuclear envelope. made of desmin, play an important role in structural and mechanical support of muscle cells. Microtubules Microtubules in a gel - fixated cell Main article : microtubule Microtubules are hollow cylinders about 23 nm in diameter ( lumen = approximately 15 nm in diameter ), most commonly comprising 13 protofilaments that, in turn, are polymers of alpha and beta tubulin. They have a very dynamic behavior, binding GTP for polymerization. They are commonly organized by the centrosome. In nine triplet sets ( star - shaped ), they form the centrioles, and in nine doublets oriented about two additional microtubules ( wheel - shaped ), they form cilia and flagella. The latter formation is commonly referred to as a `` 9 + 2 '' arrangement, wherein each doublet is connected to another by the protein dynein. As both flagella and cilia are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton. They play key roles in : intracellular transport ( associated with dyneins and kinesins, they transport organelles like mitochondria or vesicles ). the axoneme of cilia and flagella. the mitotic spindle. synthesis of the cell wall in plants. In addition to the roles described above, Stuart Hameroff and Roger Penrose have proposed that microtubules function in consciousness. Comparison Cytoskeleton type Diameter ( nm ) Structure Subunit examples Microfilaments 6 double helix actin Intermediate filaments 10 two anti-parallel helices / dimers, forming tetramers vimentin ( mesenchyme ) glial fibrillary acidic protein ( glial cells ) neurofilament proteins ( neuronal processes ) keratins ( epithelial cells ) nuclear lamins Microtubules 23 protofilaments, in turn consisting of tubulin subunits in complex with stathmin α - and β - tubulin Septins Main article : Septin Septins are a group of the highly conserved GTP binding proteins found in eukaryotes. Different septins form protein complexes with each other. These can assemble to filaments and rings. Therefore, septins can be considered part of the cytoskeleton. The function of septins in cells include serving as a localized attachment site for other proteins, and preventing the diffusion of certain molecules from one cell compartment to another. In yeast cells, they build scaffolding to provide structural support during cell division and compartmentalize parts of the cell. Recent research in human cells suggests that septins build cages around bacterial pathogens, immobilizing the harmful microbes and preventing them from invading other cells. Spectrin Main article : Spectrin Spectrin is a cytoskeletal protein that lines the intracellular side of the plasma membrane in eukaryotic cells. Spectrin forms pentagonal or hexagonal arrangements, forming a scaffolding and playing an important role in maintenance of plasma membrane integrity and cytoskeletal structure. Yeast cytoskeleton See also : Yeast In budding yeast ( an important model organism ), actin forms cortical patches, actin cables, and a cytokinetic ring and the cap. Cortical patches are discrete actin bodies on the membrane and are vital for endocytosis, especially the recycling of glucan synthase which is important for cell wall synthesis. Actin cables are bundles of actin filaments and are involved in the transport of vesicles towards the cap ( which contains a number of different proteins to polarize cell growth ) and in the positioning of mitochondria. The cytokinetic ring forms and constricts around the site of cell division. Prokaryotic cytoskeleton Main article : Prokaryotic cytoskeleton The cytoskeleton was once thought to be a feature only of eukaryotic cells, but homologues to all the major proteins of the eukaryotic cytoskeleton have been found in prokaryotes. Although the evolutionary relationships are so distant that they are not obvious from protein sequence comparisons alone, the similarity of their three - dimensional structures and similar functions in maintaining cell shape and polarity provides strong evidence that the eukaryotic and prokaryotic cytoskeletons are truly homologous. However, some structures in the bacterial cytoskeleton may not have been identified as of yet. FtsZ FtsZ was the first protein of the prokaryotic cytoskeleton to be identified. Like tubulin, FtsZ forms filaments in the presence of guanosine triphosphate ( GTP ), but these filaments do not group into tubules. During cell division, FtsZ is the first protein to move to the division site, and is essential for recruiting other proteins that synthesize the new cell wall between the dividing cells. MreB and ParM Prokaryotic actin - like proteins, such as MreB, are involved in the maintenance of cell shape. All non-spherical bacteria have genes encoding actin - like proteins, and these proteins form a helical network beneath the cell membrane that guides the proteins involved in cell wall biosynthesis. Some plasmids encode a separate system that involves an actin - like protein ParM. Filaments of ParM exhibit dynamic instability, and may partition plasmid DNA into the dividing daughter cells by a mechanism analogous to that used by microtubules during eukaryotic mitosis. Crescentin The bacterium Caulobacter crescentus contains a third protein, crescentin, that is related to the intermediate filaments of eukaryotic cells. Crescentin is also involved in maintaining cell shape, such as helical and vibrioid forms of bacteria, but the mechanism by which it does this is currently unclear. Additionally, curvature could be described by the displacement of crescentic filaments, after the disruption of peptidoglycan synthesis. Common features and differences between prokaryotes and eukaryotes By definition, the cytoskeleton is composed of proteins that can form longitudinal arrays ( fibres ) in all organisms. These filament forming proteins have been classified into 4 classes. Tubulin - like, actin - like, Walker A cytoskeletal ATPases ( WACA - proteins ), and intermediate filaments. Tubulin - like proteins are tubulin in eukaryotes and FtsZ, TubZ, RepX in prokaryotes. Actin - like proteins are actin in eukaryotes and MreB, FtsA in prokaryotes. An example of a WACA - proteins, which are mostly found in prokaryotes, is MinD. Examples for intermediate filaments, which have almost exclusively been found in animals ( i.e. eukaryotes ) are the lamins, keratins, vimentin, neurofilaments, and desmin. Although tubulin - like proteins share some amino acid sequence similarity, their equivalence in protein-fold and the similarity in the GTP binding site is more striking. The same holds true for the actin - like proteins and their structure and ATP binding domain. Cytoskeletal proteins are usually correlated with cell shape, DNA segregation and cell division in prokaryotes and eukaryotes. Which proteins fulfill which task is very different. For example, DNA segregation in all eukaryotes happens through use of tubulin, but in prokaryotes either WACA proteins, actin - like or tubulin - like proteins can be used. Cell division is mediated in eukaryotes by actin, but in prokaryotes usually by tubulin - like ( often FtsZ - ring ) proteins and sometimes ( Crenarchaeota ) ESCRT - III, which in eukaryotes still has a role in the last step of division. See also Biology portal Molecular and cellular biology portal Cell ( biology ) Organelle Nuclear matrix Microfilament References ^ Jump up to : Hardin, Jeff ; Bertoni, Gregory ; Kleinsmith, Lewis J. ( 2015 ). Becker 's World of the Cell ( 8th ed. ). New York : Pearson. pp. 422 -- 446. ISBN 978013399939 - 6. 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PMID 22314400. doi : 10.1038 / nrm3284. Jump up ^ Mascarelli A ( December 2011 ). `` Septin proteins take bacterial prisoners : A cellular defence against microbial pathogens holds therapeutic potential ''. Nature. doi : 10.1038 / nature. 2011.9540. Jump up ^ `` Calpain proteolysis of alpha - II - spectrin in the normal adult human brain ''. Neurosci. Lett. 316 ( 1 ) : 41 -- 4. December 2001. PMID 11720774. doi : 10.1016 / S0304 - 3940 ( 01 ) 02371 - 0. Jump up ^ Pruyne D, Bretscher A ( February 2000 ). `` Polarization of cell growth in yeast ''. Journal of Cell Science. 113 ( 4 ) : 571 -- 85. PMID 10652251. Jump up ^ Shih YL, Rothfield L ( September 2006 ). `` The bacterial cytoskeleton ''. Microbiology and Molecular Biology Reviews. 70 ( 3 ) : 729 -- 54. PMC 1594594. PMID 16959967. doi : 10.1128 / MMBR. 00017 - 06. Jump up ^ Michie KA, Löwe J ( 2006 ). `` Dynamic filaments of the bacterial cytoskeleton '' ( PDF ). Annual Review of Biochemistry. 75 : 467 -- 92. 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Animation of leukocyte adhesion ( Animation with some images of actin and microtubule assembly and dynamics. ) http://cellix.imba.oeaw.ac.at/ Cytoskeleton and cell motility including videos Open access review article on the emergent complexity of the cytoskeleton ( appeared in Advances in Physics, 2013 ) Structures of the cell / organelles ( TH H1. 00.01. 2 - 3 ) Endomembrane system Cell membrane Nucleus Nucleolus Endoplasmic reticulum Golgi apparatus Parenthesome Autophagosome Vesicles Exosome Lysosome Endosome Phagosome Vacuole Acrosome Cytoplasmic granules Melanosome Microbody Glyoxysome Peroxisome Weibel -- Palade body Cytoskeleton Microfilaments Intermediate filaments Microtubules Prokaryotic cytoskeleton MTOCs Centrosome Centriole Basal body Spindle pole body Myofibril Endosymbionts Mitochondrion Plastids Chloroplast Chromoplast Gerontoplast Leucoplast Amyloplast Elaioplast Proteinoplast Tannosome Other internal RNA Ribosome Spliceosome Vault Cytoplasm Proteasome External Undulipodium Cilium Flagellum Axoneme Radial spoke Extracellular matrix Cell wall Proteins of the cytoskeleton Human Microfilaments and ABPs Myofilament Actins A1 A2 C1 G1 G2 Myosins MYO1A MYO1B MYO1C MYO1D MYO1E MYO1F MYO1G MYO1H ) II MYH1 MYH2 MYH3 MYH4 MYH6 MYH7 MYH7B MYH8 MYH9 MYH10 MYH11 MYH13 MYH14 MYH15 MYH16 III MYO3A MYO3B V MYO5A MYO5B MYO5C VI MYO6 VII MYO7A MYO7B IX MYO9A MYO9B X MYO10 XV MYO15A XVIII MYO18A MYO18B LC MYL1 MYL2 MYL3 MYL4 MYL5 MYL6 MYL6B MYL7 MYL9 MYLIP MYLK MYLK2 MYLL1 Other Tropomodulin Troponin Tropomyosin Actinin Arp2 / 3 complex actin depolymerizing factors Cofilin Destrin Gelsolin Profilin Titin Other Wiskott - Aldrich syndrome protein Fibrillin Filamin FLNA FLNB FLNC Espin TRIOBP Intermediate filaments Type 1 / 2 ( Keratin, Cytokeratin ) Epithelial keratins ( soft alpha - keratins ) type I / chromosome 17 10 12 13 14 15 16 17 19 20 chromosome 12 18 none 21 type II / chromosome 12 2A 5 6A 6B 7 8 9 Hair keratins ( hard alpha - keratins ) type I / chromosome 17 31 32 33A 33B 34 35 36 37 38 type II / chromosome 12 81 82 83 84 85 86 Ungrouped alpha chromosome 17 23 24 25 26 27 28 39 40 chromosome 12 71 72 73 74 75 76 77 78 79 80 Not alpha Beta - keratin Type 3 Desmin GFAP Peripherin Vimentin Type 4 Internexin Nestin Neurofilament NEFL NEFM NEFH Synemin Syncoilin Type 5 Nuclear lamins : A / C B1 B2 Microtubules and MAPs Kinesins KIF1A KIF1B KIF2A KIF2C KIF3B KIF3C KIF4A KIF4B KIF5A KIF5B KIF5C KIF6 KIF7 KIF9 KIF11 KIF12 KIF13A KIF13B KIF14 KIF15 KIF16B KIF17 KIF18A KIF18B KIF19 KIF20A KIF20B KIF21A KIF21B KIF22 KIF23 KIF24 KIF25 KIF26A KIF26B KIF27 KIFC1 KIFC2 KIFC3 Dyneins axonemal : DNAH1 DNAH2 DNAH3 DNAH5 DNAH6 DNAH7 DNAH8 DNAH9 DNAH10 DNAH11 DNAH12 DNAH13 DNAH14 DNAH17 DNAI1 DNAI2 DNALI1 DNAL1 DNAL4 cytoplasmic : DYNC1H1 DYNC2H1 DYNC1I1 DYNC1I2 DYNC1LI1 DYNC1LI2 DYNC2LI1 DYNLL1 DYNLL2 DYNLRB1 DYNLRB2 DYNLT1 DYNLT3 Other Tau protein Dynactin DCTN1 Tubulins TUBA1A TUBA1B TUBA1C TUBA3C TUBA3D TUBA3E TUBA4A TUBA8 Stathmin Tektin TEKT1 TEKT2 TEKT3 TEKT4 TEKT5 Dynamin DNM1 DNM2 DNM3 Catenins Alpha catenin Beta catenin APC Plakoglobin ( gamma catenin ) Delta catenin GAN Membrane Dystrophin Dystroglycan Utrophin Ankyrin ANK1 ANK2 ANK3 Spectrin SPTA1 SPTAN1 SPTB SPTBN1 SPTBN2 SPTBN4 SPTBN5 Other Plakins Corneodesmosin Desmoplakin Dystonin Envoplakin MACF1 Periplakin Plectin Talin TLN1 Vinculin Plakophilin PKP1 PKP2 Nonhuman Major sperm proteins Prokaryotic cytoskeleton Crescentin FtsZ MreB See also : cytoskeletal defects GND : 4121944 - 2 NDL : 00576209 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Cytoskeleton&oldid=806444098 '' Categories : Cell anatomy Cytoskeleton Hidden categories : Articles which use infobox templates with no data rows Wikipedia articles with GND identifiers Talk Contents About Wikipedia বাংলা Български Bosanski Català Čeština Cymraeg Dansk Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Gaelg Galego 한국어 Հայերեն हिन्दी Hrvatski Bahasa Indonesia Íslenska Italiano עברית Қазақша Latina Latviešu Lëtzebuergesch Lietuvių Magyar Македонски Nederlands 日本 語 Norsk Occitan Polski Português Română Русский Scots සිංහල Simple English سنڌي Slovenčina Slovenščina کوردی Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska Tagalog தமிழ் ไทย Українська اردو Tiếng Việt 中文 Edit links This page was last edited on 22 October 2017, at 02 : 01. 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Question: the smallest of the cytoskeleton elements is the
Answer: Microfilaments