25 – Mitosis Flashcards
Cyclin synthesis
timer of cell cycle
-accumulaiton of cyclin=increase of cyclin dpendent kinase = cell progress thorugh cell cycle
Mitosis - 2 jobs
1. perfectly Segregate your chromosomes
6 phases of Mitosis
o Interphase
o Prophase
o Prometaphase
o Metaphase
o Anaphase
o Telophase
o Cytokinesis
How to build a mitotic spindle? 4 steps
- Push the centrosomes apart
-End of S phase : Duplication of centrioles = 2 spindle poles - Put spindle in right place
-Between mother & daughter (bud) cell - Connect chromosomes to microtubules
- Segregate the chromosomes
who does the work in mitosis?
Motor proteins
-Mitosis = mechanical
-Bc were moving things around
Kinesin & dynein
Engines of mitosis
They are what generate the movement and reorganization of the
chromosomes and of the mitotic spindle.
Kinesin
Motor protein: converts the energy of ATP hydrolysis into force.
walks to microtubule plus end
Kinesin-5
tetrameric kinesins = slide anti-parallel microtubules
Pushes apart the microtubules = drive away the mitotic spindle
Pushes the centrosomes apart = bipolar structure
Monastrol
drug = inhibit kinesin-5
If used, we get monopolar spindle
centrosomes can’t spread apart.
The two spindle poles stay collapsed on top of one another.
Microtubules are emanating away from them in a radial array.
Nuclear envelope breaks down, the microtubules bind to the chromosomes
get bouquet of chromosomes surrounding spindle.
Not all cells
divide down the middle = asymmetric position of mitotic spindle
Asymmetric division
C.elegans
C.elegans
-Smaller daughter cell = germline gametes & protein contents
-Larger daughter cell = all other somatic cell & less protein contents
how does asymmetric division happen?
Break where spindle is placed = how is it determined = interact with cell cortex
Dynein
Minus end directed motor protein -> carry cargo
responsible for Positioning mitotic spindle
Microtubule pulled by anchored dynein into the cortex
Getting rid of dynein
disrupt spindle positioning
if you get rid of any of the proteins involved in dynein and it’s anchoring
RNA interference of a dynein intermediate chain 1.
RNA interference of an anchoring protein that binds the dynein to the spindle.
RNAI effect becomes dominant, the positioning of the spindle becomes aberrant.
You no longer get the movement.
- the spindle just starts wandering around aimlessly.
- spindle just kind of goes dead and stops moving.
And in both cases, lead to problems with germline specification.
what does kinesin 5 and dynein do?
Kinesin 5 is pushing these spindle poles apart.
Microtubules are emanating from the spindle poles being grabbed by dynein, and dynein is pulling on them & positions the spindle in place
rate of turnover of the microtubules in the spindle
poleward flux
microtubule flux toward pole
Kinesin-13
create poleward flux of microtubules
Depolymerize microtubules from (-) ends
-Pull microtubule toward spindle pole
Position at spindle poles
Kinetochores
big sleeves for microtubules
Wrap end of microtubule & stay attached whether growing/shrinking
There are … at kinetochore…
motors:
Kinesin-7 = keep it attached & walk to + end
Kinesin-13 = depolymerizes
Each protein gives a little force vector
-Bc it is carrying fragile cargo
-Need all of them to make chromosome move = its big
Add all force vector = net force determines which direction to move
Microtubule depolymerization
drives chromosome movements
Pull chromosomes apart = becomes shorter = energy released = movement
Kinesin-13 & depolymerization, what happens? what does it lead to?
KInesin 13 triggers catastrophe and depolymerization events.
The microtubule start splaying outward and leads to a downward force that push the kinetochord down towards the - end.
depolymerization of the microtubules pulls the the chromosomes apart.
as the chromosomes are moving towards the spindle pole,
microtubules that are connecting to the pole are getting shorter
as they move, they are de polymerizing and the free energy that is released by depolymerization=responsible for the movement
how the spindle is built by motor proteins
slide these poles apart = anti parallel sliding of microtubules by kinesin 5.
position our spindle correctly within the cytoplasm = pulling of microtubules by anchored cytoplasmic dyne
create a treadmill of the microtubules moving continuously towards the spindle pole (poleward flux) = kinesin 13 located at spindle
move our chromosomes to the metaphase plate = kinetochore, a large multi protein complex full of motors where a large number of forces worked together to position the chromosomes at the spindle equator.
