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In all cells of all domains of life (archaea, bacteria, eukaryotes) a cytoskeleton is found (notably in all eukaryotic cells, which include human, animal, fungal and plant cells). The cytoskeleton can be referred to as 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. However, the structure, function and dynamic behaviour of the cytoskeleton can be very different, depending on organism and cell type. Similarly, within the same cell type the structure, dynamic behaviour, and function of 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 shape and mechanical resistance to deformation,〔 so that through association with extracellular connective tissue and other cells it stabilizes entire tissues.〔〔 The cytoskeleton can also actively 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. ==Eukaryotic cytoskeleton== Eukaryotic cells contain three main kinds of cytoskeletal filaments: microfilaments, microtubules, and intermediate fillaments Each cytoskeletal filament has a shape and intracellular distribution. Additionally, the filaments are formed by polymerization of different types of sub-units. The microfilament consist of the polymers of the protein actin which has a diameter of 7 nm. The microtubules are made up of the protein called tublin which has a diameter of 25 nm. Intermediate filaments are made up of various proteins which varies depending on the cell type. These type of filament normally have diameters ranging from 8-12 nm 〔.〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cytoskeleton」の詳細全文を読む スポンサード リンク
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