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Lect. 05 F10 - Microtubule Assembly and Function...

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Microtubule Assembly and Function Tetrahymena , a ciliated protozoan
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Microtubule organization and function Organization of the microtubule cytoskeleton 1) Microtubules extend from the center of the cell throughout the cytoplasm 2) Microtubules function as tracks on which to transport cellular cargo 3) Microtubules form the mitotic spindle. 4) Microtubules are responsible for ciliary and flagellar movement.
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Inside the cell, microtubule assembly is nucleated from a fixed point, the microtubule organizing center or centrosome colchicine - a drug that binds to free tubulin subunits, causing microtubule disassembly prior to treatment with colchicine recovery after microtubule disassembly centrosome
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QuickTimeª and a GIF decompressor are needed to see this picture. QuickTimeª and a GIF decompressor are needed to see this picture. At the centrosome, γ -t ubulin forms a r ing c omplex ( γ -TuRC) that removes the kinetic barrier to nucleating microtubule assembly The γ -tubulin ring complex is thought to form a platform that allows new microtubules to readily assemble. QuickTimeª and a GIF decompressor are needed to see this picture.
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centriole electron dense centrosome matrix (contains γ -TuRC) electron micrograph of a centrosome The minus ends of microtubules are embedded in the centrosome
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Nucleotide binding necessary for assembly. Free energy of nucleotide hydrolysis not required for assembly per se, but is required for MTs to exhibit dynamic assembly properties that are important for cytoskeleton function. Basically, nucleotide hydrolysis allows MTs and to disassemble rapidly. Assembly of GTP-tubulin activates intrinsic GTPase activity. Free energy of hydrolysis results in conformational changes favoring GDP-tubulin disassembly. Uncouples assembly and disassembly reactions. Think of this as a race between subunit incorporation and nucleotide hydrolysis. If subunit addition occurs faster than hydrolysis, net polymerization. If hydrolysis catches up, filament end prone to disassemble. Tubulin-GTP Tubulin-GDP Which end do you think will have a harder time keeping up with the rate of nucleotide hydrolysis? What is the role of nucleotide hydrolysis in microtubule assembly?
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What is the role of nucleotide hydrolysis (cont) Assembly/disassembly of GTP-tubulin and assembly/disassembly of GDP- tubulin are different reactions.
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