chapter 9 - cytoskeleton notes.docx

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Biological Sciences
Rene E Harrison

Cytoskeleton a skeletal system Composed of three structuresMicrotubules MicrofilamentsIntermediate filamentsEach of the three types of cytoskeletal laments is a polymer of protein subunits held together by weak noncovalent bondsMicrotubules are long hollow unbranched tubes composed of subunits of the protein tubulinMicrolaments are solid thinner structures often organized into a branching network and composed of the protein actinIntermediate laments are tough ropelike bers composed of a variety of related proteins Functions of Cytoskeleton 1 A dynamic scaffold providing structural support 2 An internal framework responsible for positioning the various organelles within the interior of the cell 3 A network of tracks that direct the movement of materials and organelles within cells 4 The forcegenerating apparatus that moves cells from one place to another Study of the CytoskeletonUsed in live cell fluorescence imaging Used in vitro and in vivo single molecule assaysUsed in atomic force microscopyMicrotubulesmicrotubules are hollow relatively rigid tubular structures and they occur in nearly every eukaryotic cell Microtubules are components of a diverse array of structures including the mitotic spindle of dividing cells and the core of cilia and agellaMicrotubules have an outer diameter of 25 nm and a wall thickness of approximately 4 nmThe wall of a microtubule is composed of globular proteins arranged in longitudinal rows termed protolamentsmicrotubules are seen to consist of 13 protolaments aligned side by side in a circular pattern within the wallEach protolament is assembled from dimeric building blocks consisting of one alpha tubulin and one beta tubulin subunitAll of the protolaments of a microtubule have the same polarityOne end of a microtubule is known as the plus end and is terminated by a row of beta tubulin subunits The opposite end is the minus end and is terminated by a row of alpha tubulin subunitsMicrotubules prepared from living tissue typically contain additional proteins called microtubuleassociated proteins or MAPsMAPs comprise a heterogeneous collection of proteins
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