L23 - Friday,November19,2010...

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Friday, November 19, 2010 Cell Movements I: Subcellular Freeways Reading: section)  Objectives It has become increasingly clear that cells are highly  organized o Early biochemists: a "bag of enzymes" o Later biochemists: many enzymes are in organelles, but the organelles float  around freely o Current wisdom: organelles are arranged in specific ways, highly  organized. It is also clear that cells and intracellular structures are extremely  dynamic The system that allows cells to be organized and dynamic is the  cytoskeleton     .     o Consists of a network of interconnected  tubules and filaments  in the  cytosol. o Gives cells shape and mechanical strength. o Serves as a scaffold for the movement of organelles. The two major classes of cytoskeletal elements are  microtubules  and  microfilaments . (A third class is intermediate filaments, but they are more  specialized and variable in function.)  Microtubules:  o 25 nm in diameter (about 1/4 the diameter of a clathrin-coated vesicle) o made up of polymerized  tubulin Microfilaments:  o 7 nm in diameter o made up of polymerized  actin Microtubule assembly is initiated at the  microtubule-organizing center (MTOC) a.k.a. the  centrosome
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Microtubules (and actin filaments) have a polarity: the two ends are different.  EACH END IS POLYMERIZED. NORTH/SOUTH o One end is arbitrarily called plus ("+"), the other minus ("-"). o The minus end of every microtubule is anchored in the MTOC. Thus,  microtubules can only grow at their plus ends. Microtubules
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This note was uploaded on 02/09/2011 for the course BIOS 20182 taught by Professor Lahn during the Spring '11 term at UChicago.

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L23 - Friday,November19,2010...

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