CFM2: Cytoskeleton

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  1. Microtubule functions
    • Cell shape
    • Cell division
    • Intracellular transport
    • Cell motility
    • Positioning of organelles
    • Other specialized functions
  2. Marginal band
    Microtubule structure in platelets that give the platelets their shape
  3. Best source of microtubules and why
    Brain (neurons are highly asymmetric and have extensive microtubule network)
  4. How to purify microtubules
    • Take brain tissue, make cold to decrease hydrophobic interactions between microtubules
    • Spin in centrifuge, discard the pellet (organelles and other stuff)
    • Add glycerol (water sequestering agent) and GTP to supernatant
    • Increase temperature to allow hydrophobic interactions to occur again
    • Spin, take the pellet (which is now the microtubules)
    • Resuspend the pellet in cold temperature and repeat the cycle
  5. Structure of protofilament
    • 13 subunits arranged around hollow core
    • a- and b-tubulin heterodimer arranged in head to tail position
  6. Polarity of protofilament
    • a- and b-tubulin heterodimers arranged in head to tail position
    • + end at alpha end; - end at beta end
  7. 2 examples of molecular motors from class and how they work
    • Kinesins: anterograde transport (towards the + end)
    • Dyneins: retrograde transport (towards the - end)
    • Both work by hydrolysis of ATP for energy and "walk" along the microtubule
  8. Drugs that influence microtubule polymerization
    • Depolymerizing (e.g. colchicine, nocodazole): depolymerize microtubules, inhibiting mitosis
    • Polymerizing (e.g. vinca alkaloids, taxol): stabilize microtubule filaments and prevent normal spindle formation during mitosis
    • For chemotherapy, give polymerizing drugs because the depolymerizing ones are too poisonous
  9. - end of microtubules is anchored on the ____
  10. Centrosome
    Main site of microtubule synthesis in the cell; where the - end is anchored
  11. Centriole structure
    9 triplets of tubulin
  12. Exchangeability of GTP in microtubules
    • Binding site of GTP on a-tubulin is non-exchangeable because the binding site is stuck between a- and b-tubulin (always GTP)
    • Binding site of GTP on b-tubulin is exchangeable
  13. Theory of dynamic instability
    • The reason why there is no simple equilibrium between tubulin heterodimers and microtubule polymers
    • When GTP-bound tubulin heterodimer is at + end of growing polymer, GTP hydrolysis is triggered
    • Tubulin is an enzyme
    • If the rate of GTP hydrolysis exceeds the rate of addition of subunits, the cap will shrink and be lost, triggering depolymerization
    • If the rate of GTP hydrolysis is slower than the rate of addition of subunits, the GTP cap will grow and the polymer will continue to grow
    • In vivo, since the microtubule polymer is anchored to the centrosome at the – end, depolymerization can only go as far as the centrosome. And, in fact, since there are several GTP “caps” throughout a polymer (GTP hydrolysis is imperfect), it will only depolymerize back to the previous GTP cap
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CFM2: Cytoskeleton
2015-09-03 13:38:24
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