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actin filament
protein filament, about 7-nm wide, formed from a chain of globular actin molecules. a major constituent of the cytoskeleton of all eukaryotic cells and especially abundant in muscle cells.
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cell cortex
specialized layer of cytoplasm on the inner face of the plasma membrane. in animal cells it is an actin-rich layer responsible for cell-surface movements.
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centriole
short cylindrical array of microtubules, usually found in pairs at the center of a centrosome in animal cells. also found at the base of cilia and flagella (and called basal bodies).
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centrosome (cell center)
centrally located organelle of animal cells that is the primary microtubule-organizing center and separates to form the two spindle poles during mitosis. in most animal cells it contains a pair of centrioles.
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cilium (plural cilia)
hairlike extension of the surface of a cell with a core bundle of microtubules and capable of performing repeated beating movements. cilia in large numbers drive the movement of fluid over epithelial sheets as in the lungs.
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cytoskeleton
system of protein filaments in the cytoplasm of a eukaryotic cell that gives the cell shape and the capacity for directed movement. it's most abundant components are actin filaments, microtubules, and intermediate filaments.
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dynamic instablility
the property shown microtubules of growing and shrinking repeatedly through the addition and loss of tubulin subunits from their exposed ends.
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dynein
member of a family of large motor proteins that undergo ATP-dependent movement along microtubules. dynein is responsible for the bending of cilia.
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filopodium (plural filopodia)
long thin actin-containing extension on the surface of an animal cell. sometimes has an exploaratory function, as in a growth cone.
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flagellum (plural flagella)
long, whiplike protrusion that drives a cell through a fluid medium by its beating. eukaryotic flagella are longer versions of cilia; bacterial flagella are completely different, being smaller and simpler in construction.
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intermediate filament
fibrous protein filament (about 10 nm in diameter) that forms ropelike networks in animal cells. often used as a structural element that resists tension applied to the cell from outside.
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kinesin
a large family of motor proteins that use the energy of ATP hydrolysis to move along a microtubule.
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lamellipodium
dynamic sheetlike extension on the surface of an animal cell, especially one migrating over a surface.
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microtubule
long, stiff, cylindrical structure composed of the protein tubulin. used by eukaryotic cells to regulate their shape and control their movements.
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motor protein
protein such as myosin or kinesin that uses energy derived from ATP hydrolysis to propel itself along a protein filament or polymetric molecule.
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myofibril
long, highly organized bundle of actin, myosin, and other proteins in the cytoplasm of muscle cells that contracts by a sliding filament mechanism.
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myosin
type of motor protein that uses ATP to drive movements along actin filaments. Myosin II is a large protein that forms thick filaments of skeletal muscle. Smaller myosins, such as myosin I, are widely distributed and are responsible for many actin-based movements.
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nuclear lamina
fibrous layer on the inner surface of the inner nuclear membrane formed as a network of intermediate filaments made from nuclear lamins.
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polarity
refers to a stucture such as an actin filament or a fertilized egg that has an inherent asymmetry-so that on end can be distinguished from the other.
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rho protein family
family of small GTPases involved in signaling that causes a rearrangement of the actin cytoskeleton.
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sarcomere
repeating unit of a myofibril in a muscle cell, about 2.5 micrometers long, composed of an array of overlapping thick (myosin) and thin (actin) filaments.
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tubulin
protein from which microtubules are made.
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