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Mitosis (What are the three major processes that are important for…

- - - - site for attachment of mitotic spindle to chromosome
      - necessary for sister chromatids to be separated
    - - 2 large subunits
        
        SMC1 and SMC3
        
        large coiled proteins with ATPase domain at one end
        
        held together by Scc1 and Scc3 to form single ring structure
  - - - each spindle pole is focused at an organelle called the centrosome
        
        composed of 2 centrioles arranged perpendicular to one another
        
        rings of gamma-tubulin protein act as nucleating centres for microtubules
        
        microtubules form the spindle
        
        during late prophase the mitotic spindle poles move to opposite sides of the cell, but they maintain an array of overlapping spindles between them.
      - contains variety of different microtubules
        
        astral microtubles
        
        radiate out from the poles into the cytoplasm
        
        help to position the spindle within the cell
        
        interpolar microtubules
        
        interdigitate at the spindle equator
        
        help to stabilise the mitotic spindle and tether the two poles together
        
        Kinetochore microtubules
        
        connect the spindle poles with the kinetochores of sister chromatids ensuring that the sister chromatids are attached to opposite spindle poles
    - - breakdown of the nuclear envelope
      - alignment of the chromosomes along the equator
    - - a collection of proteins that associates with the centromere
      - allows the spindle fibres to attach to the chromosomes.
    - - chromosomes are orientated and lined up along the equator of the cell
  - - - prophase
        
        facilitated by protein condensin
        
        contains 2 large subunits with ATPase domain
        
        held together by 3 CAP proteins
        
        forms ring complex
        
        undergo 4 levels of packing
        
        generation of mitotic chromosomes
        
        nuclear enveloppe still intact
        
        newly assembled spindles are visible
    - - separation of sister chromatids
      - two distinct modes of movement
        
        shortening of the kinetochore microtubules
        
        pulling the sister chromatids in opposite directions
        
        movement of the actual spindle poles
  - - - pinches cell into two
      - actin and myosin fibres
      - local activation of the small GTPase RhoA that triggers the assembly and contraction of the ring
        
        RhoA is activated by a RhoGEF protein and inactivated by a Rho GTPase-activating protein (RhoGAP).
        
        The active GTP-bound form of RhoA is focused at the future cleavage site
        
        By binding proteins called formins, activated RhoA promotes the assembly of actin filaments in the contractile ring.
        
        By activating Rho-activated protein kinases, such as Rock, it stimulates myosin II filament formation and activity,
        
        contraction of the ring.
    - - sister chromatids arrive at opposite poles of the spindle
      - chromosomes decondense
      - nuclear enveloppe reforms
        
        when enveloppe is completely reformed = end of mitosis
- - - - mitosis
        
        nuclear division occurs
      - cytokinesis
        
        cytoplasm divides
        
        1 cell physically splits to generate 2 daughter cells
- - - - activation of APC
        
        activation of Cdc20
        
        ubiquination + destruction of securin
        
        destruction of securin allows separase to cleave Scc1, a subunit of the cohesin complex holding the sister chromatids together thereby cleaving the cohesins