The cytoskeleton (also CSK) is a cellular "scaffolding" or "skeleton" contained within the cytoplasm. Scaffolding is a temporary framework used to support people and material in the construction or repair of buildings and other large structures In Biology, the skeleton is a strong and often a rigid framework that supports the body of an animal holding it upright and giving it shape and strength (Also skeletal The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. The cytoskeleton is present in all cells; it was once thought this structure was unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex The prokaryotic cytoskeleton is the collective name for all structural filaments in Prokaryotes. It is a dynamic structure that maintains cell shape, often protects the cell, enables cellular motion (using structures such as flagella, cilia and lamellipodia), and plays important roles in both intracellular transport (the movement of vesicles and organelles, for example) and cellular division. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it A cilium (plural cilia) is an Organelle found in eukaryotic cells Cilia are tail-like projections extending approximately The lamellipodium (pl Lamellipodia) is a cytoskeletal Actin projection on the mobile edge of the A vesicle is a small bubble of liquid within a cell A more formal definition in Cell biology, would be that a vesicle is a relatively small intracellular membrane-enclosed Cell division is a process by which a cell, called the parent cell divides into two or more cells called daughter cells.
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The eukaryotic cytoskeleton
Eukaryotic cells contain three main kinds of cytoskeletal filaments, which are microfilaments, intermediate filaments, and microtubules. The House Mouse ( Mus musculus) is one of the most numerous species of the genus Mus commonly termed a Mouse. An embryo (from Greek:, plural, lit "that which grows" from en- "in" + bryein "to swell be full" is a multicellular A fibroblast is a type of cell that synthesizes and maintains the Extracellular matrix of many Animal tissues Phalloidin is one of a group of Toxins from the death cap ( Amanita phalloides) known as Phallotoxins It binds Actin, preventing its Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex The cytoskeleton provides the cell's cytoplasm with structure and shape.
Actin filaments / Microfilaments
- Further information: Actin
Around 7 nm in diameter, this filament is composed of two intertwined actin chains. Microfilaments (or actin filaments) are the thinnest filaments of the Cytoskeleton found in the cytoplasm of all Eukaryotic cells. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of Microfilaments are most concentrated just beneath the cell membrane, and are responsible for resisting tension and maintaining cellular shape, forming cytoplasmatic protuberances (like pseudopodia and microvilli- although these by different mechanisms), and participation in some cell-to-cell or cell-to-matrix junctions. The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer Pseudopods or pseudopodia (from the Greek word ψευδοπόδια, ψευδός "fake false" Microvilli (singular microvillus) are microscopic cellular membrane protrusions that increase the surface area of cells and are involved in a wide variety of functions including In association with these latter roles, microfilaments are essential to transduction. In Biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another They are also important for cytokinesis (specifically, formation of the cleavage furrow) and, along with myosin, muscular contraction. Cytokinesis is the process whereby the Cytoplasm of a single Eukaryotic cell is divided to form two daughter cells In Cell biology, the cleavage furrow is the indentation that begins the process of cleavage, by which Animal and some algal cells Myosins are a large family of Motor proteins found in Eukaryotic tissues. Skeletal muscle is a type of Striated muscle, which usually attaches to tendons Actin/Myosin interactions also help produce cytoplasmic streaming in most cells. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of Myosins are a large family of Motor proteins found in Eukaryotic tissues. Cytoplasmic streaming is the flowing of Cytoplasm in Eukaryotic cells.
Intermediate filaments
These filaments, 8 to 12 nanometers in diameter, are more stable (strongly bound) than actin filaments, and heterogeneous constituents of the cytoskeleton. Intermediate filaments (IFs are cytoskeletal structures formed by members of a family of related proteins called Keratin. Like actin filaments, they function in the maintenance of cell-shape by bearing tension (microtubules, by contrast, resist compression. Microtubules are one of the components of the Cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers It may be useful to think of micro- and intermediate filaments as cables, and of microtubules as cellular support beams). Intermediate filaments organize the internal tridimensional structure of the cell, anchoring organelles and serving as structural components of the nuclear lamina and sarcomeres. In Eukaryotic cells during Interphase, there is a bilayered Nuclear envelope surrounding the nucleus, which separates the Cytoplasm and its "A-band" redirects here For other uses of the term see A band. They also participate in some cell-cell and cell-matrix junctions.
Different intermediate filaments are:
- made of vimentins, being the common structural support of many cells. Vimentin is a member of the Intermediate filament family of proteins
- made of keratin, found in skin cells, hair and nails. Keratins are a family of fibrous structural proteins; tough and insoluble they form the hard but nonmineralized structures found in Reptiles Birds The skin is the outer covering of living tissue of an animal (or plant Hair is a keratinised protein filament that grows through the epidermis from follicles deep within the Dermis. A nail is a horn -like structure at the end of an animal's Finger or Toe.
- neurofilaments of neural cells. Neurofilaments are the 10 nanometer (10nm or Intermediate filaments found specifically in neurons
- made of lamin, giving structural support to the nuclear envelope. Lamins are Fibrous proteins providing structural function and transcriptional regulation in the Cell nucleus.
Microtubules
Microtubules are hollow cylinders about 25 nm in diameter (lumen = approximately 15nm in diameter), most commonly comprised of 13 protofilaments which, in turn, are polymers of alpha and beta tubulin. Microtubules are one of the components of the Cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers A Tubulin is one of several members of a small family of globular Proteins The most common members of the tubulin family are α-tubulin and β-tubulin the proteins that They have a very dynamic behaviour, binding GTP for polymerization. Guanosine-5'-triphosphate ( GTP) is a Purine Nucleotide. One role is as substrate for the synthesis of RNA during transcription. They are commonly organized by the centrosome. In Cell biology, the centrosome is an Organelle that serves as the main Microtubule organizing center (MTOC of the animal cell as well
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. A Centriole is a barrel shaped Organelle found in most animal Eukaryotic cells though absent in Higher plants and Fungi. The latter formation is commonly referred to as a "9+2" arrangement, wherein each doublet is connected to another by the protein dynein. Dynein is a Motor protein (also called molecular motor or motor molecule in cells which converts the chemical Energy contained in ATP into the 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). Dynein is a Motor protein (also called molecular motor or motor molecule in cells which converts the chemical Energy contained in ATP into the Kinesins are a class of Motor proteins found in Eukaryotic cells In Cell biology, an organelle (pronunciation /ɔː(rgəˡnɛl/ is a specialized subunit within a cell that has a specific function and is usually separately enclosed In Cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed Organelle found in most eukaryotic cells. A vesicle is a small bubble of liquid within a cell A more formal definition in Cell biology, would be that a vesicle is a relatively small intracellular membrane-enclosed
- the axoneme of cilia and flagella. Chlamydomonas TEM 17jpg|thumb|Micrograph of thin x-section cut through Chlamydomonas axoneme]]Numerous Eukaryotic cells carry whip-like appendages ( Cilia A cilium (plural cilia) is an Organelle found in eukaryotic cells Cilia are tail-like projections extending approximately A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it
- the mitotic spindle. In Cell biology, the spindle apparatus (also called spindle fibers) is the structure that separate the Chromosomes into the daughter cells during
- synthesis of the cell wall in plants.
Comparison
| Cytoskeleton type | Diameter (nm) [1] | Structure | Subunit examples[1] |
|---|---|---|---|
| Microfilaments | 8-10 | double helix | actin |
| Intermediate filaments | 8-10 | two parallel helices/dimers, forming tetramers | |
| Microtubules | 25 | protofilaments, in turn consisting of tubulin subunits | α- and β-tubulin |
Microtrabeculae - a further structural network?
A fourth eukaryotic cytoskeletal element, microtrabeculae, was proposed by Keith Porter based on images obtained from high-voltage electron microscopy of whole cells in the 1970s. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a Microfilaments (or actin filaments) are the thinnest filaments of the Cytoskeleton found in the cytoplasm of all Eukaryotic cells. In Geometry a double helix (plural helices) typically consists of two congruent helices with the same axis differing by a translation Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of Intermediate filaments (IFs are cytoskeletal structures formed by members of a family of related proteins called Keratin. A helix (pl helixes or helices) from the Greek word έλιξ, is a special kind of Space curve, i Vimentin is a member of the Intermediate filament family of proteins Mesenchyme refers to loosely organized connective tissue present in the embryo regardless of origin Glial fibrillary acidic protein (GFAP is an Intermediate filament (IF Protein that is found in Glial cells such as Astrocytes, but also in Glial cells, commonly called neuroglia or simply glia (Greek for "glue" are non- Neuronal cells that provide support and nutrition Neurofilaments are the 10 nanometer (10nm or Intermediate filaments found specifically in neurons Keratins are a family of fibrous structural proteins; tough and insoluble they form the hard but nonmineralized structures found in Reptiles Birds In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body Lamins are Fibrous proteins providing structural function and transcriptional regulation in the Cell nucleus. Microtubules are one of the components of the Cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers Microtubules are one of the components of the Cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers A Tubulin is one of several members of a small family of globular Proteins The most common members of the tubulin family are α-tubulin and β-tubulin the proteins that A Tubulin is one of several members of a small family of globular Proteins The most common members of the tubulin family are α-tubulin and β-tubulin the proteins that An electron microscope is a type of Microscope that uses Electrons to illuminate a specimen and create an enlarged image The images showed short, filamentous structures of unknown molecular composition associated with known cytoplasmic structures. Porter proposed that this microtrabecular structure represented a novel filamentous network distinct from microtubules, filamentous actin, or intermediate filaments. It is now generally accepted that microtrabeculae are nothing more that an artefact of certain types of fixation treatment though we have yet to fully understand the complexity of the cell's cytoskeleton[2].
The prokaryotic cytoskeleton
The cytoskeleton was previously thought to be a feature only of eukaryotic cells, but homologues to all the major proteins of the eukaryotic cytoskeleton have recently been found in prokaryotes. The prokaryotic cytoskeleton is the collective name for all structural filaments in Prokaryotes. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex In Evolutionary biology, homology has come to mean any similarity between characters that is due to their shared ancestry. The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other [3] 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. Proteins are an important class of biological Macromolecules present in all biological organisms made up of such elements as Carbon, Hydrogen [4]
FtsZ
FtsZ was the first protein of the prokaryotic cytoskeleton to be identified. FtsZ is a Protein encoded by the ftsZ Gene that assembles into a ring at the future site of the Like tubulin, FtsZ forms filaments in the presence of GTP, but these filaments do not group into tubules. Guanosine-5'-triphosphate ( GTP) is a Purine Nucleotide. One role is as substrate for the synthesis of RNA during transcription. 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. Cell division is a process by which a cell, called the parent cell divides into two or more cells called daughter cells. A cell wall is a tough flexible and sometimes fairly rigid layer surrounding a cell, located external to the Cell membrane, which provides the cell with structural
MreB and ParM
Prokaryotic actin-like proteins, such as MreB, are involved in the maintenance of cell shape. MreB is a protein found in bacteria that has been identified as a homologue of Actin, as indicated by similarities in Tertiary structure and conservation 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. History See also History of genetics The existence of genes was first suggested by Gregor Mendel (1822-1884 who in the 1860s studied inheritance Biosynthesis is a phenomenon wherein Chemical compounds are produced from simpler Reagents Biosynthesis unlike Chemosynthesis, takes place within living
Some plasmids encode a partitioning system that involves an actin-like protein ParM. A plasmid is an extra-chromosomal DNA molecule separate from the chromosomal DNA which is capable of replicating independently of the chromosomal DNA ParM is a Prokaryotic Actin homologue which provides the force to drive copies of the R1 plasmid to opposite ends of rod shaped Bacteria 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. Microtubules are one of the components of the Cytoskeleton. They have a diameter of 25 nm and length varying from 200 nanometers to 25 micrometers Two structures in biology are said to be analogous if they perform the same or similar function by a similar mechanism but evolved separately Mitosis is the process in which a Eukaryotic cell separates the Chromosomes in its Cell nucleus, into two identical sets in two daughter nuclei
Crescentin
The bacterium Caulobacter crescentus contains a third protein, crescentin, that is related to the intermediate filaments of eukaryotic cells. Caulobacter crescentus is a Gram-negative, Oligotrophic Bacterium widely distributed in fresh water lakes and streams Crescentin is a Protein which is a Bacterial relative of the Intermediate filaments found in Eukaryotic cells. Crescentin is also involved in maintaining cell shape, but the mechanism by which it does this is currently unclear.
References
- ^ a b Unless else specified in boxes, then ref is:Walter F. , PhD. Boron (2003). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders, 1300. ISBN 1-4160-2328-3. Page 25
- ^ Heuser J (2002). "Whatever happened to the 'microtrabecular concept'?". Biol Cell 94 (9): 561-96. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
- ^ Shih YL, Rothfield L (2006). "The bacterial cytoskeleton". Microbiol. Mol. Biol. Rev. 70 (3): 729–54. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16959967.
- ^ Michie KA, Löwe J (2006). "Dynamic filaments of the bacterial cytoskeleton". Annu. Rev. Biochem. 75: 467–92. doi:. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16756499.
Further reading
- Linda A. Amos and W. Gradshaw Amos, Molecules of the Cytoskeletion, Guilford, ISBN 0-89862-404-5, LoC QP552. C96A46 1991
External links
- Cytoskeleton, Cell Motility and Motors - The Virtual Library of Biochemistry and Cell Biology
- Cytoskeleton database, clinical trials, recent literature, lab registry ...
- Animation of leukocyte adhesion (Animation with some images of actin and microtubule assembly and dynamics. )
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