Cell cycle and chromosome movement

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  1. APC activation
    • -          APCCdc20  becomes activated prior to metaphase and ubiquitinates a key anaphase inhibitor called securin—so named because it secures the attachment between sister chromatids
    • o   the ubiquitination and destruction of securin at the end of metaphase reelase an active protease called separase
    • §  separase cleaves the Scc1 subunit of the cohesin molecule that holds sister chromatids together
  2. Cleavage
    • o   cleavage of cohesin triggers the separation of sister chromatids to mark the onset of anaphase
    • -          Near the end of mitosis, Cdc20 is inactivated, and the alternate adaptor, Cdh1, takes control of the APC’s substrate selection
    • o   When Cdh1 is associated with the APC, the enzyme completes the ubiquitination of cyclin B that was begun by APCCdc20
    • §  this destruction of cyclin leads to a drop in activity of the mitotic Cdk and progression of the cell out of mitosis and into the G1 phase of the next cell cycle
    • ·         if this destruction doesn’t occur, cells are arrested in the late stage of mitosis
  3. checkpoint
    • -          there is a checkpoint at the transition between metaphase and anaphase: spindle assembly checkpoint, which occurs when a chromosome fails to become aligned properly at the metaphase plate, causing delay of anaphase until proper positioning occurs
    • o   unattached kinetochores contain a complex of proteins, one being Mad2, that mediates the spindle assembly checkpoint
    • §  these proteins send a wait signal to prevent anaphase
    • §  only when properly attached does the wait signal turn off
  4. inhibition
    • -          Inhibition is achieved through direct interaction between Mad2 and the APC activator Cdc20.
    • o   when Cdc20 is bound to Mad2, APC complexes can’t ubiquitinate securing, keeping the sister chromatids together
    • -          Another signal may be the attachment of sister chromatids by microtubules from the same spindle pole, called syntelic attachment
    • o   this is resolved by Aurora B kinase which phosphorylates the protein substartes, destabilizing microtubule attachment and allowing the kinetochores to reattach 
  5. Chromosome movement
    __ of the chromosomal microtubules during anaphase was both a consequence and cause of chromosome movement; it involves two processes
    Depolymerization
  6. Microtubules undergo what...

    These combined activities lead to ...
    • -          The microtubules that comprise the chromosomal spindle fibers undergo depolymerization at both their minus and plus ends during anaphase
    • -          these combined activities lead to the movement of chromosomes toward the pole:
    • o   Depolymerization at the minus ends transports the chromosomes towards the poles due to poleward flux
    • o   depolymerization at the plus ends serves to “chew up” the fiber that is towing the chromosomes
  7. Force required
    • -          The force required for chromosome movement is provided by the release of strain energy as the microtubule depolymerizes
    • o   the released energy is utilized by the curled ends of the depolymerizing protofilaments to bias the movement of the bound heads of the Ndc80 complex
  8. Function of cell wall 
    1
    Develop turgor pressure to provide shape and support
  9. Function of cell wall 
    2
    Serves as a type of skeleton for the entire plant
  10. Function of cell wall 
    3
    Protect the cell against damage from mechanical abrasion and pathogens, and they mediate cell-cell interactions
  11. Function of cell wall 
    4
    Source of signals that alter the activities of the cells it contacts
  12. Types of macromolecules: hemicelluloses
    • Structure: Branched polysaccharides whose backbone consists of one sugar, such as glucose and side chains of other sugars, such as xylose
    • Function: bind to the surfaces of cellulose microfibrils, cross-linking them into a resilient structural network
  13. Types of macromolecules: pectin
    • Structure: heterogeneous class of negatively charged polysacchardies containing galacturonic acid
    • Function: hold water and form an extensive hydrated gel that fills in the spaces between the fibrous elements; upon release, they trigger a defensive response
  14. Types of macromolecules: proteins
    • Structure: there are numerous types
    • Function: mediate dynamic activities
  15. How Cell Walls arise
    • 1)      first, as a thin cell plate that forms between the plasma membranes of newly formed daughter cells following cell division
    • 2)      matures by incorporation of additional materials that are assembled inside the cell and secreted intot eh extracellular space
    • 3)      the primary walls are formed first and, as cellulose content increases, they become secondary walls composed of lignin

Card Set Information

Author:
 DesLee26
ID:
 252238
Filename:
 Cell cycle and chromosome movement
Updated:
 2013-12-10 05:58:14
Tags:
Bio final
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Mickle
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