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2024 Cell Biology > 6: Microtubule Functions > Flashcards

6: Microtubule Functions Flashcards

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1
Q

What is the function of a microtubule? What does it need to carry out this function?

A
  • vescile transport in both directions and at different speeds
  • requires motor proteins which need ATP energy
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2
Q

model orgamism for MT transport?

A

squid axon

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3
Q

how is axonal transport studied?

A
  1. radioactive AAs injected into large axon body
  2. this makes radioactive proteins
  3. some of these proteins get transported towards + end of MT
  4. isolate different fragments of the axon and run on SDS page gel
  5. each fragment is a different distance from initial injection site
  6. proteins get separated on the gel and you will see bands of different sizes
  7. repeat process at several time intervals and run on separate gel to see movement of proteins by the different band sizes
  8. notice that some proteins move faster than others and some proteins move in groups
  9. isolate protein bands to determine what the protein is and which proteins work together
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4
Q

axonal transport does not occur through

A

diffusion

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5
Q

What is kinesin?

A

Microtubule’s plus end directed motor protein

moves towards plus end

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6
Q

What is the structure of kinesin? What function do each component have?

ATP is used for

A

2 heavy chains: head (ATPase activity and MT binding ability), flexible neck/linker and stalk regions
2 light chains: variable (depending on cargo recognizing and binding)

movement to (+) end by linker region bending

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7
Q

What would a kinesin protein look like on an SDS page?

A

2 heavy chains are the same = 1 high MW band
2 variable light chains = 2 low MW bands

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8
Q

kinesin has similar movement to

A

myosin (actin motor protein)

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9
Q

What is kinesin 1?

structure

A
  • conventional - found in cytoplasm
  • 2 same heavy chains and 2 sometimes variable light chains
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10
Q

What is kinesin 2?

structure

A
  • heterotrimeric
  • 2 different heavy chains + 1 light chain-like

3 bands on SDS page

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11
Q

kinesin 1 and 2 are involved in

A

organelle transport

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12
Q

What is kinesin 5?

structure + function + location

A
  • bipolar (has 4 heavy chains - one on each side) ie 2 head domains and 2 linker regions on each side
  • involved in mitosis
  • does not bind to cargo - binds to stalk domain of another 2 heavy chains
  • sits between parallel MTs for MT sliding
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13
Q

What is kinesin 13?

structure + function

A
  • uses ATP hydrolysis to remove dimers off MT ends (depolymerization)
  • heavy chain (2 head domains + linker/neck)
  • not moving towards (+) end
  • can remove from both (+) and (-) end, but usually (-) end has proteins bound to in
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14
Q

In kinesin, ATP hydrolysis causes

A

conformation change of kinesin = head moves 16nm (dimer is 8nm) = antereograde (towards + end) movement

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15
Q

how do we stop kinesin from movement when there is no cargo?

A
  • heavy chains folded so that head domain can’t bind to MT
  • no ATPase activity
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16
Q

What is cytoplasmic dyenein?

A
  • MT minus end directed motor protein for retrograde transport
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17
Q

What is the structure of cytoplasmic dyenein

A
  • 2 heavy chains have 2 head domains (with ATPase and MT binding, linker/neck region and stalk)
  • linker bends for movement
  • stem = tail
  • linker + stem (tail) interact with dynactin hetero complex to recognize and bind cargo
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18
Q

What is dynamitin?

A

protein in dynactin heterocomplex that helps release cargo when it reaches location

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19
Q

What is P150glued?

A
  • binds to MT
  • no motor force
  • helps hold dyenein + cargo in place
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20
Q

kinesin and dynein can move

A

proteins (including kinesin moving dynein to plus end so it can function again) and organelles (ex. golgi, lysosome, mito)

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21
Q

How is tubulin modified? Why do we use this method instead of MAPs?

A

posttranslational acetylation of lysin residue of alpha tubulin

this stabilizes MT and promotes kinesin-1 movement

MAPs can get in the way of transportation

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22
Q

differences between cilia and flagella?

A

cilia: 2-10um and sweeps material acriss tissue (many)
flagella: 10-2000um and propels cells (few)

23
Q

what is an axoneme?

A

underlying structure of cilia and flagella

24
Q

what does an axoneme look like?

A
  • 9+2 array: surrounded by 9 doublet MTs which are connected by nexin with 2 singlet MTs in the middle (function unknown)
    -** radial spoke heads **are attached to A tubule of outer doublets facing centre - holds structure in place
  • **axonemal dyein: **permanently bound to A tubule and head domains projects towards B tubule of next doublet
  • all MTs are stable
  • > 250 proteins
25
Q

How is basal body related to axoneme?

A

basal body is MTOC for cilia and flagella: triplet MT in basal corresponds to doublet MT in axoneme (same number) and the transitional zone is the area between triplet and doublet

basal body may or may not have central singlet MTs

26
Q

cilia/flagella usually come in

A

pairs

27
Q

similarity & differences btwn basal bodies and centrioles

A

2 basal bodies/centrioles 90 degrees to eo
both MTOC

basal bodies directly polymerized into the axonemes BUT centrioles do not generate singlet MT, these singlets arise from PCM

28
Q

axonemal dyenein is attached to the

A

A tubule of the triplet in the axoneme (cilia and flagella)

29
Q

how does cilia/flagella move?

A
  • a pair of MT- nexin links them and dynein head is attached to one and head domain reaches to the other
  • if there is nothing holding the MTs together = sliding (not in axoneme bc nexin + basal body + radial spoke heads holds in place)
  • head of axonemal dynein is minus end directed motor – when head moves, causes localized bending bc sliding can’t occur

only some MTs will be bound to each other - bending is localized

30
Q

cilia and flagella (as long projections) can be used as

A

antenna (to receive and give signals)

secrete ligands & have signal receptors

31
Q

how does intraflagellar transport occur?

A

movement of material up and down unrelated to bending by using cytoplasmic dynein for retrograde to minus end and kinesin for antereograde to plus end

32
Q

cilia and flagella signaling antenna is important in

A

embryos

33
Q

many interphase cells contain

A

a non-motile primary cilium (no axonemal dynein)

antenna like for cell-cell signalling

also found in embryos

34
Q

primary cilia are

A

stabilized by acetylated tubulin and not found in mitotic cells

35
Q

2 components of mitosis are

A

karyokinesis: dividing chromosomes and MTs
cytokinesis: dividing cytoplasm and actin

36
Q

What happens to the cytoskeleton in interphase?

A

antereograde and retrograde transport (long half-life) change to be responsible for chromosome separation rearrange (very short half-life0

centrosomes duplicate (2 -> 4)

37
Q

interphase MT are – from mitotic MT

A

different

38
Q

What happens to the cytoskeleton in prophase?

A

breakdown of interphase microtubule array and its replement by mitotic asters which separate

39
Q

What happens to the cytoskeleton in prometaphase?

A

chromosomes captured and brought to spindle equator

40
Q

What happens to the cytoskeleton in metaphase?

A

chromosomes aligned by spindle fibers

MTOC centrosomes = poles

pole MT are different from centriole MT

41
Q

What happens to the cytoskeleton in anaphase?

A

spindle pole separation

42
Q

how are pole different from centrioles?

A

centrioles:
* interphase
* antereograde and retrograde transport MTs
* gamma tubulin ring complex at minus end = no depoly
* fast half-life 5 mins
* more stable MT

poles:
* mitosis
* spindle apparatus
* different mechanism for polymerization and nucleating much faster
* short half-life 15sec
* less stable MT
* depoly at minus end possible

43
Q

What causes mitotic MT instability?

A

XMAP215 activity decreases in mitosis = unstable

44
Q

types of MT in mitotic apparatus

A

SPINDLE
polar MT: MT growing towards another pole, but doesn’t reach a chromosome

kinetochore MT: holds chromosome by kinetochore protein

–

astral MT: grows not towards other pole

45
Q

kinetochore proteins are attached to

A

plus end of MT (such that it can still polymerize and depolymerize)

46
Q

how do all chromosomes align at metaphase plate?

A
  • movement by poly and depoly of MTs (poly + kinesin on one side and depoly + dynein on other)
  • kinesin and dynein help MTs move to move everything to metaphase plate (ie plus and minus end directed proteins)
47
Q

what must occur by the spindle apparatus?

A

all chromosomes must be captured on BOTH sides

48
Q

what happens with the chromosome is not attached on both sides?

A

Ndc80 captures MT = conformational change of Ndc80

without tension, Ndc80 gets phosphorylated by Aurora B kinase

phosphorylated Ndc80 lets go of MT

49
Q

what happens with the chromosome is attached on both sides?

A

Ndc80 captures MT = conformational change of Ndc80

with tension, Aurora B kinase is inhibited = no phosphorylation = movement of chromosome to metaphase plate

50
Q

What is the function of astral MT?

A

bind to dynein (which are on ends of cells and bound to PM)

pole and active cortical anchor are minus end = dynein walks towards minus end to pull the pole by astral MT towards the side that is far from metaphase plate

other side is inactive cortical anchor

51
Q

What are the two phases of anaphase?

A

A: chromosome moves closer to pole by kinetechore MT shortening by depoly of minus and plus end
B: poles push away from metaphase plate + cell elongating requiring motors

52
Q

how does anaphase B occur?

A

polar MTs overlap and sliding between these by kinesin 5 (+ end directed motors so that heads move towards respective + ends) to undo overlap = pushing poles apart

can polymerize more on + ends so kinesin 5 can keep pushing

dynein pulling astral MT also pulls poles apart + astral MT depolymerizes at + end

53
Q

What is RhoGTP used for in mitotic spindle apparatus?

A

gets localized by polar MTs, RhoGTP localizes actin which allows for contracile actin/myosin ring at metaphase plate

ring is formed as far away from 2 new forming nuclei

2024 Cell Biology (4 decks)

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