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Unformatted text preview: 13-1Cell and Molecular Biology (Biol. Chem. 410A)Lecture #13Harry R. Matthews, Ph.D.October 14, 1996CytoskeletonClinical correlations: vinblastine, vincristine, taxolAlzheimer's disease Learning objectives: Cytoskeleton microtubules microfilaments intermediate filaments molecular motors (kinesin, dynein) actin, tubulinOptional reading:Stryer IV: Chapter 15he cytoskeleton is an important part of mammalian cells, providing structure and organization within the cell.TThe cytoskeletonEukaryotic cells contain many filamentous structures that determine the overall shape of the cell, allow it to move and provide a struc-ture within the cytoplasm on which many cel-lular events take place. This structure is very complex, involving hundreds of different pro-teins, and is known as the cytoskeleton. The filaments of the cytoskeleton are classified into 3 groups: microtubules, microfilaments and intermediate filaments.MicrotubulesMicrotubules are made from the protein tu-bulin. They play a major role in organizing the cytoplasm and provide the substrate on which proteins and vesicles can be actively transpor-ted from one part of the cell to another. Micro-tubules are found in cells throughout the body and are especially prominent in nerve cells in the brain.Each tubulin molecule is a heterodimer of -tubulin and -tubulin. The tubulin genes comprise a small family of - and - tubulins which probably have specific functions. However, the formation of microtubules is a common function for all tubulins. A microtu-bule is a long, thin, hollow cylinder, or tube, of 25 nm diameter. The walls of the cylinder are made from 13 long thin protofilaments, aligned parallel to each other, thatviewed on-endmake a 13-sided polygon that ap-proximates the cylindrical structure. Each protofilament is a string of - and - tubulin subunits alternating along the protofilament. Thus, one end of a protofilament is an -tu-bulin molecule while the other end is a -tu-bulin. The protofilaments align in a parallel fashion (as opposed to anti-parallel) so that one end of a microtubule is the beginning of a long helix of -subunits with 13 residues per turnfrom an end-on view it looks like a ring of 13 subunits. Similarly, the other end is the beginning of a long helix of -subunits that looks like a ring of 13 subunits when viewed end-on. The two ends behave differently as seen below....
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- Spring '03