12-9-09_MicrotubuleMotors_lectureA

12-9-09_MicrotubuleMotors_lectureA - The most exciting...

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The most exciting phrase to hear in science, the one that heralds new discoveries, is not 'Eureka!' but 'That's funny. ..' Isaac Asimov I think I'm a clone now There's always two of me just a-hangin' around I think I'm a clone now 'Cause every chromosome is a hand-me-down "I Think I'm A Clone Now“ Weird Al Yankovic
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Announcements Quiz 9 (last one!) due today at noon Please complete online course evaluations by December 13 My office hours will be 9-10 AM Monday and Tuesday next week
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Cellular motor videos http://www.youtube.com/watch?v=9ICqcZ99qGk (microtubule dyn.) http://www.youtube.com/watch?v=ZL3_BwrB6AM (dyn. Instabil) http://www.youtube.com/watch?v=9iXoXzgmEXw (microtub + ER) http://www.youtube.com/watch?v=686qX5yzksU (kinesin) http://www.youtube.com/watch?v=vJ9ffKeUCvE (myosin) http://vcell/ndsu.edu/animations/ (nice videos on cell trafficking, secretion, insulin signaling, and lac operon model)
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Microtubules are made of tubulin dimers α-tubulin and β-tubulin exist in dimers. β-subunit has a bound GDP, which is exchanged for GTP during microtubule assembly α-subunit has a bound GTP that is non-exchangeable These dimers assemble in α-β-α-β-α-β chains called protofilaments .
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Microtubules are polarized and form helical cylinders Staggering of adjacent protofilaments creates helix that is 3 subunits high/per full turn A seam is formed where alpha and beta subunits are directly adjacent to each other Protofilaments are asymmetric ( α -tubulin at one end, β -tubulin at other), giving them a polarity. All protofilaments of microtubule have same Plus end - fast-growing ( β -tubulins on tip); minus end - slow-growing ( α -tubulins on tip) Polarity important for growth and transport Example: Axon, all plus-end distal. Dendrite, plus and minus-end distal
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Microtubule organizing centers Two stage formation of microtubules First is nucleation when initial portions of microtubule form Second is elongation In vitro, nucleation is slow. Made fast in cell by having microtubule organizing centers Best-studied is centrosome involved in organizing mitotic cell division Centrioles in the centrosome nucleate microtubules centriole
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Gamma-tubulin is necessary for microtubule nucleation Gamma-tubulin colocalizes in all microtubule organizing centers Small proportion of total tubulin Gamma-subunits thought to bind to “ring complexes” of centrioles in centrosome, which are the same diameter as microtubules Alpha-beta heterodimers (beta on plus- end tip) can then bind to these gamma starter subunits
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Assembly of microtubules requires GTP GTP is bound to beta subunit of a soluble heterodimer
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This note was uploaded on 02/09/2010 for the course BIOL 230 taught by Professor Bartlett,e during the Fall '08 term at Purdue University-West Lafayette.

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12-9-09_MicrotubuleMotors_lectureA - The most exciting...

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