slide set 13 Flashcards

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1
Q

microtubules can

A

rapidly reorganize in response to cellular cues

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2
Q

microtubules are….

A
  • required for intracellular organization
  • responsible for chromosome movement in mitosis
  • involved in long range vesicle transport
  • involved in directional persistence in cell motility
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3
Q

what do microtubules assemble from

A

tubulin dimers
alpha and beta tubulin

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4
Q

microtubule polarity

A

start with a very stable microtubule structure (axoneme) and introduce purified tubulin

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5
Q

dynamic instability of microtubule assembly/disassembly

A

microtubules switch between a state of assembly and a state of disassembly

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6
Q

dynamic instability diagram GTP GDP

A
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7
Q

regulation of microtubule assembly

A

a series of proteins regulate microtubule assembly in time and space

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8
Q

nucleators

A

help determine organization of the array

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9
Q

gamma-tubulin

A

present in microtubules in smaller concentrations than alpha and beta tubulins

involved in nucleation of microtubule growth in yeast to humans

microtubules are nucleated from a specific intracellular location (microtubule-organizing center - MTOC)

gamma-tubulin is most enriched in MTOC

nucleation sometimes depends on gamma tubulin ring complex Y-TuRC

within Y-TuRC, 2 accessory proteins bind directly to gamma-tubulin and several other proteins to create a spiral ring (this acts as a template for the microtubule)

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10
Q

microtubule nucleation by gamma-tubulin ring complex

A

A. 2 copies of gamma tubulin associate with a pair of accessory proteins to form the gamma-tubulin small complex (TuSC)

Y-TuRC nucleates minus end of microtubule

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11
Q

centrosome structure

A

complex with centrioles at center

centrioles are surrounded by proteins that hold the ring complex nucleation sites

centrioles = arrangement of microtubules into stable cylinders

centriole is major MTOC of animal cells

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12
Q

do microtubule arrays need a centrosome to organize themselves?

A

NO!

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13
Q

+TIPs protein

A

remains associated with growing plus ends and can link them to other structures such as membranes

EB1 binds microtubule plus ends

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14
Q

balance of regulators at MT plus end tips

A

various proteins control transition between microtubule growth and shrinkage

catastrophe factors (kinesin-13) bind to microtubule ends and pry them apart, promoting depolymerization

MAPs (ex: XMAP215) stabilizes the end of a growing microtubule

XMAP215 binds tubulin dimers and delivers them to the microtubule plus end (increases growth rate and suppresses catastrophes)

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15
Q

balance of regulators at MT plus end tips

A

balance of regulators regulate the length and organization of the microtubule array

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16
Q

cargo transport

A

microtubules help with cargo transport

17
Q

kinesin and dyneins

A
  • kinesin: walks towards plus end of MT
  • dynein: walks towards minus end of MT (dying is bad = - end)
  • transport vesicles, organelles, mRNAs, protein complexes, other MTs, chromosomes)
18
Q

how kinesins move

A
  1. rear head of kinesin detaches from tubulin binding site, passes the partner motor domain, and then rebinds to the next available tubulin binding site (hand over hand motion)
    1. can travel long distances
  2. rear or lagging head is tightly bound to microtubule and ATP
  3. front or leading head is loosely bound to the microtubule with ADP in its binding site
  4. forward displacement of rear motor domain is driven by the dissociation of ADP and binding ATP in the leading head
  5. binding of ATP to motor domain causes a small peptide (neck linker) to shift from rearward to frontward conformation
  6. this pulls rear head forward once it has detached from the microtubule with ADP bound (detachment requires ATP hydrolysis and Pi release)
  7. kinesin is now ready for next step (repeat the process)
19
Q

2 ways to walk on a MT

A

kinesin walks, dynein uses inchworm

20
Q

dynactin

A

dynein works in complex with dynactin and links to vesicles via Arp1 filaments