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1- Cell division 23 Oct (2- phases of the cell cycle (mitosis (pro phase…

- - - - they will rearrenge their position as well as the position of DNA throughout the cell division using kinesin and dynein
    - - the nuclear lamina has to change their assembly throughout the cell division
    - - one extreme eg. of actin filament changes during cell division is a contractile ring form at the end of the cell division which is in the cytokinesis phase
- - - - what happens at interphase:
        
        s phase: replication of DNA and replication of centrosome
        in interphase the morphology wise cell looks like to the one on the right hand side
        
        NOT very condensed brown DNA siting everywhere whitin the nucleus
        
        one centrosome light green centre of mictotubule
        -dynamically growing and shrinking microtubules
        
        No interaction between nucleus and microtubule
        
        at the end of the enterphase right before going to actual dividing phase
        
        you need to have double the content of DNA whithin the nucleus
        flowing around everywhere
        a pair of centrosome so they can divide into 2
        
        why do you think DNA is floating everywhere in nucleus rather than being compact as sister cromatid?
        
        better to be uncoiled to be transcribed to make protein
        DNA has to be read into messenger RNA and then protein
        so if it is hardly coiled you need to uncoil it everytime you do any work so makes sense not to have any condensed DNA form within the nucleus
        
        1 more item...
  - - - a little of condensation happening
        a little bit of white parts in the nucleus symbolising DNA becoming of coiled structure
      - mitosis spindle forming --- :!?: being ready
    - - nuclear envelop will be gone
        microtubule can go in and start interacting with the sister chromatid>>> the coiled condensed form of DNA
    - - they finish connecting the microtubule to the sister chromatid
        they are ready to pull then away
    - - pull microtubule away from eachother
      - devide the pair , each twards the centrosome
    - - finished with pulling them apart
        
        protect DNA information within nucleas envelope
        
        forming a nulear envelop
        see a little bit of actin ring
- - - - G1/S- cyclin shoots up
    - - S-cycling will shoots up
    - - M-cyclin will shoot up
- - - - one kinetochore has to bind to one centrosome and the other side of that pair has to be bound to the centrosome attach to the other side of the centrosome
        
        there will be a lot of trial and error
- - - - no nuclear envelop
- - - - you see 2 groups of chromosome rather than one in the middle at metaphase
- - - - we call this centrosome spindle pole
        
        ASTRAL microtubule :star: does not interact with microtubule from the other side of the centrosome
        they are helping positioning the spindle pole
        interacting with the other portion or cell membrane
        
        Kinetochore microtubule :star:
        we have microtubules interacting with microtbules from other side through kinetochore
        impor. role : making perfect binding so they can do the job of dividing the chromosome into same 2 portions
        
        interpolar microtubule :star:
        direct interaction
        there are a lot of dynein and kinesin
        interpola mic. will help positioning the spindle pole to the other spindle pole , so you push it away then cenrtosome will be further apart
        if you want to pull them then centrosome will be closer to eachother
- - - - which is not perfect yet
        
        there will be still a centrosome, interpolar microtubule still existing to control the position of these 2
        
        if you dont have the middle green ones as interpolar microtubule
        
        you dont have a great control of each centrosome, they might interact together and there might be a mix of the chromosome betw. those 2 which is not good
- - - - they pinch it and it becomes 2 separate entity
        
        interpolar microtubule will be gone soon
  - - - it becomes smaller and smaller
        
        you find a lot of cleavage furrow structure
        
        that is the midbody right before they are aparting
  - - - which will end up promoting the actin filament formation as well as myosin 2 activation which will both work together
        
        to make the contractile ring become more contractile so they can pinch out into 2 separate entity
- - - - will pull the centrosome closer to theother centrosome
    - - kinesin 14 move to minus end
    - - kinesin 5 will move to plus end in both sides
        that is going to be very efficient puting 2 centrosome together closer to eachother
    - - use kinesin 4 and 10 and move around the actual chromatin chromosome to be able to put in the right position
        
        kinetochor microtubule to make perfect binding
- - - - microtubule just randomely going near the sister chromatid
        
        those structure crossing with anti parallel cross linking at a nucleation level and then later they form some actual antiparallel structure with some kinesin and dynein and other types od kinesin will come in and move around those actual chromatin to the minus or plus end so they can fing the edge of microtubule which they have to actually bind
        
        diagram on the bottom right:
        energy wise when you dont have pathic ??? binding from the microtubule from the either side >>> it is enegetically not very stable
        
        when kinetochore microtubule make a perfect binding to the kinetochore from either side will be more stable
        
        keep trying until they find the perfect binding stats
- - - - until the metaphase the 2 chromosome has to be perfectly paired
        
        that is the job of protein cohesin :star:
        a ring structure wrapping around 2 sister chromatids so they are pair
        
        when APC kicks in it will degrage the securin which secure the inactive form of separase
        
        APC/C :star: will degerade the securin then inactive seperase can become active
        
        Active separase will seperate the cohesin
        
        there is no more ring so the kinetochore microtybul or interpolar microtubule pull away those sister chromatids into either side of the pole
- - - - until telophase, more structured nuclear envelop forming in telophase
        but not totally intact as interphase but at the end of the cell division you'll get the nuclear envelop back to normal again
        
        if you want to stain nuclear lamina, during cell division, you should be able to draw what that staining look like through out cell division
        
        summary slide has the key pints in cell division