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MCB 2007 September 26th October 1st and October 3rd Lecture Notes

MCB 2007 September 26th October 1st and October 3rd Lecture Notes

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September 26 th and October 1 st Lecture Notes: The Cytoskeleton (chapter 17…continued) Microtubules (continued) o Motor proteins drive intracellular transport along microtubules most cellular molecules move within a cell via salutatory movements…do not rely on random thermal motion motor proteins bind to microtubules (or actin filaments) and use the energy derived from ATP hydrolysis to travel along the filament in a single direction carry vesicles, organelles can move at a speed of up to 10 cm/day main tool of research: Squid giant axon (axoplasm was extruded and examined using video-enhanced microscopy) teeming cytoplasm…could observe vescicles and organelles (especially mitochondria) moving along filamentous tracks Kinesins are a family of ATP-dependent, + end directed motor proteins have a very large gene family (serve a wide variety of functions, move many different things within a cell), specialized ones exist for mitosis structure: o light chains (head domain…attaches to cargo), very variable across the protein family o heavy chains (legs and feet) which attach to the microtubule and “walk” along it o linked with a coiled-coil domain move progressively towards the + end of the microtubule via ATP hydrolysis (ATP binds heavy chain to MT, other foot is swung out; ADP and phosphate are released, foot is released) Dyneins - end directed motors are either flagellar or cytosolic (very few genes) o cytosolic dyneins bring substances back (from the + end) and flagellar are responsible for cell motility very large ( > 1000000 daltons) consist of a heavy chain (foot domains), light chain, and intermediate chain help center the mitotic apparatus, anchor the plus end of microtubules to the plasma membrane help position the Golgi apparatus (move it inwards along microtubules)
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much less specific than kinesins (larger light chains/head domains) Microtubules help to arrange the organelles in a eukaryotic cell Golgi apparatus is moved inwards via dyneins Endoplasmic reticulum is moved outwards via kinesins (is pulled and stretched outwards) energy is provided with kinases (regulate the phosphorylation of proteins with ATP)…ATP hydrolysis governs the movement of motor proteins and thus the movement of organelles and vesicles within a cell
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Intermediate Filaments o 10 nm filaments, not composed of one single protein dimer o are very strong and rope-like have great tensile strength (consist of many filaments twisted around each other in a coiled-coil formation, like a rope) very important in maintaining a cell’s structure subunits = elongated fibrous proteins that have a N-terminal globular head, a C-terminal globular tail, and a central elongated
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