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C HAPTER 9: T HE C YTOSKELETON A ND C ELL M OTILITY Overview of the Major Functions of the Cytoskeleton I. Cytoskeleton - composed of 3 well-defined filamentous structures that form an elaborate interactive network; has functions analogous to that of skeleton (support cell & play key role in mediating cell movements) A. Each of the 3 cytoskeletal filaments is a polymer of protein subunits connected to one another by weak, noncovalent bonds 1. Such construction lends itself to rapid assembly & disassembly, which is dependent upon complex cellular regulation 2. Each cytoskeletal element has distinct mechanical properties B. The 3 types of cytoskeletal elements 1. Microtubules (MTs) - hollow, rigid cylindrical tubes with walls composed of tubulin subunits 2. Microfilaments (MFs) - solid, thinner structures composed of actin 3. Intermediate filaments (IFs) - tough, ropelike fibers composed of a variety of related proteins II. Function in number of interrelated activities they are highly dynamic; can do rapid & dramatic reorganization; often require accessory proteins that are not part of filaments A. Dynamic scaffold; provides structural support that helps determine cell shape (ex.: RBC spectrin- actin) & resist forces that tend to deform it 1. The flat, rounded shape of many cultured cells depends on a radial array of MTs in cell cytoplasm B. Internal framework that is responsible for positioning organelles in cell interior (ex.: polarized epithelial cells - organelles arranged in defined pattern along an axis from the apical to the basal end of the cell) C. A network of tracks that direct the movement of materials & organelles within the cell 2. Movement of membranous carriers from ER to Golgi complex 3. Transport of vesicles containing neurotransmitters down the length of the nerve cell; carry vesicles from synthesis site to axon terminal. D. Force-generating apparatus - move cells from place to place (cilia, flagella, pseudopodia) 1. Single-celled organisms - crawl over surface of solid substratum or propel themselves through aqueous environment with aid of specialized locomotor organelles (cilia & flagella protruding from cell surface) 2. Multicellular animals have variety of cells capable of independent locomotion - sperm, white blood cells, fibroblasts, highly motile tip of growing axon (its movement resembles crawling blood cell) F. Separation of chromosomes during mitosis & meiosis & cytokinesis (splitting parent cell into two daughter cells); essential component of cell's division machinery The Study of the Cytoskeleton II. The use of live-cell fluorescence imaging traditional light microscopy is tool used to learn about cell organization within fixed stained tissues & to observe the motile activities of living cells A. New technique allows us to view things below resolution limit of regular light scopes (too small); used to study dynamics of cytoskeleton in live cells fluorescence microscope; known as live-cell imaging... View Full Document

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