341lecture34dec7sakai

341lecture34dec7sakai - Cell Biology 341 Last lecture:...

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Cell Biology 341 Monday, December 7, 2009 Today: Dynamic instability of microtubules Structure of microfilaments Bring #2 pencils for SETs Last lecture: Began chapter 16: the cytoskeleton Intermediate filaments are composed of fibrous proteins such as keratin and lamins (nucleus) Microtubules (MT) radiate outward from the centrosome , and are also found in the mitotic spindle, cilia and flagella Microtubules are hollow tubes composed of α -tubulin/ β -tubulin heterodimers in 13 protofilaments Both α and β-tubulin bind GTP The (+) ends of microtubules grow outward from the centrosome, where growth begins at the (-) end on a ring of γ -tubulin
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Microtubules (and actin filaments) exhibit dynamic instability : a period of growth followed by rapid disassembly Each tubulin molecule binds GTP on both the α and β subunits, but the GTP of α-tubulin is never hydrolyzed
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A GTP cap favors assembly of microtubules If growth is slower than GTP hydrolysis, the dimers on the end will contain GDP-tubulin, and disassembly will be favored If growth is rapid, the end dimers will contain GTP, forming a GTP cap that stabilizes the MT MT must undergo rapid assembly and disassembly during the formation of structures such as the mitotic spindle Figure 16-16 + end - end
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Actin filaments ( microfilaments
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341lecture34dec7sakai - Cell Biology 341 Last lecture:...

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