Lecture 15 (Oct 3)

Lecture 15 (Oct 3) - Biological Sciences 110A Introduction...

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Lecture 15: Microtubule Structure & Function  Overview of the cytoskeleton   Microtubules are polymers of  α/β  tubulin dimers  The centrosome: the microtubule organizing center  Microtubules are dynamically unstable: GTP cap  Regulation by microtubule associated proteins (MAPs)  Microtubules in cell structure and transport  Directional microtubule motors: Kinesins, Dyneins  Microtubule-based flagella and cilia Biological Sciences 110A: Introduction to Biology Kendal Broadie Reading in Chapter 9 (328-356) Karp
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Overview of Cytoskeleton Types and Functions Fig. 9.1 Karp
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Most eukaryotic cells contain a cytoskeleton composed of three protein filament  systems Microtubules Intermediate filaments Microfilaments 25 nm 25 nm 25 nm 25 nm dia. Tubulins ( α  and  β ; MAPs and  motor proteins) Vesicle transport, cell polarity, and  division 9-12 nm dia. Cell-type specific subunits Elasticity and tensile strength  (“rope function”) 6-7 nm dia. Actin (myosin motor, and  accessory proteins) Contraction, transport,  locomotion and division
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Our focus today: MICROTUBULES 1) Large, stiff, hollow protein tubes  2) Structural support, organization, transport
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MTs are composed of  α - and  β -tubulin dimers α - and  β -Tubulin are evolutionally-related: ~35% identical amino acids ~50% sequence similarity Highly conserved between species: ~80%  identical yeast to humans Both  α - and  β -tubulin bind guanine  nucleotides (GTP): GTP in  α -TB is not hydrolyzed GTP in  β -Tb hydrolyzed during assembly  (controls stability) Tubulin dimers assemble into MTs… Tubulin (100 kda) α β α β Tubulin (subunit) GTP See Fig. 9.8 Karp
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Tubulin dimers assemble into MTs MTs are composed of  α - and  β -tubulin dimers 25 nm dia. 8 9 10 11 12 13 2 3 4 5 6 7 1 Plus-end ( β -end) Minus-end ( α -end) Protofilaments 13 Tubulin (100 kda) α β α β Tubulin (dimer subunit) A network of  protein tubes See Fig. 9.8 Karp
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In most animal cells, MTs are nucleated by the centrosome Green = tubulin Red = Centrosomes Centrosomes Centrosome = m icrot ubule o rganizing c enter (MTOC) See Fig. 9.10, 9.22 Karp
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Lecture 15 (Oct 3) - Biological Sciences 110A Introduction...

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