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Microtubules - Topic 3 The cytoskeleton Reading Chapter...

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Topic 3 – The cytoskeleton Reading Chapter 2.5d, 2.5e, 9.3, 36.1b On-line sources (read selectively) Objectives BIO 1140 – SLIDE 1 Functions of cytoskeleton Structure and function of microtubules Structure and function of filaments Microfilaments Intermediate filaments Emphasis on the dynamic nature of the cytoskeleton Fig. 2.22 Functions of the Functions of the cytoskeleton cytoskeleton – an overview an overview Functions include: The provision of structure and support (1) Intracellular transport (2) BIO 1140 – SLIDE 2 The positioning of organelles within the cell (4) The generation of force for cell movement Contributing to cell division Fig. 9.1, Karp et al. 2010 Microtubules Introduction Hollow, tubular structures of diameter ~25 nm found in all eukaryotic cells Two basic types Cytoplasmic – very dynamic Axonemal – very stable BIO 1140 – SLIDE 3 Fig. 2.22 Fig. 2.25 - three basic areas where cytoskeleton is imp: structure, transport, and organizing contents of cell - cytoskeleton is imp for movement of cell and movement of molecules throughout cell - - cytoskeleton provides structure, organizing contents, and movement within and of cell - walls made of protein - microtubules can be found in cytoplasm of cell - spread throughout entire cytoplasm - form network - also find them in cilia and flagella - very stable - in flagella and cilia - called axonemal microtubules
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Structure Building block is ß-tubulin globular GTP binding site Only ß-tubulin hydrolyzes GTP Protofilament – structural polarity + end = ß-tubulin - end = -tubulin Microtubule = 13 protofilaments BIO 1140 – SLIDE 4 Fig. 17-10, Alberts et al. 2004 ß-tubulin -tubulin Dynamic character Polymerization when GTP bound to ß-tubulin of the ß-dimer (tubulin-GTP) Hydrolysis follows polymerization Dissociation more likely when GDP bound to ß-tubulin of the ß-dimer (tubulin-GDP) Dynamic instability model Rate of hydrolysis > rate of tubulin GTP ß-tubulin - GDP Dissociates readily ß-tubulin - GTP Polymerizes readily ß ß + end New ß-tubulin-GTP dimers BIO 1140 – SLIDE 5 Rate of hydrolysis > rate of tubulin-GTP addition Microtubule-binding proteins regulate the rate of assembly and stability of microtubules MAPs (microtubule-associated proteins) Useful drugs Colchicine Taxol - end Hydrolysis of GTP on ß- but not -tubulin All ß units have GDP Dynamic character Polymerization when GTP bound to ß-tubulin of the ß-dimer (tubulin-GTP) Hydrolysis follows polymerization Dissociation more likely when GDP bound to ß-tubulin of the ß-dimer (tubulin-GDP) Dynamic instability model Rate of hydrolysis > rate of tubulin GTP BIO 1140 – SLIDE 6 Rate of hydrolysis > rate of tubulin-GTP addition Microtubule-binding proteins regulate the rate of assembly and stability of microtubules MAPs (microtubule-associated proteins) Useful drugs Colchicine Taxol Fig. 15-7, Becker et al. 2006
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