Motor Proteins in Mitosis and Stages in formation of the Mitotic Spindle

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DesLee26
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252237
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Motor Proteins in Mitosis and Stages in formation of the Mitotic Spindle
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2013-12-10 00:52:24
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Bio Final
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  1. Prophase
    • Accompanied by movement of spindle poles to opposite ends of the cell
  2. Prometaphase
    movement of hte chromosomes too the spindle equator
  3. Anaphase A
    movement of chromosomes from the metaphse plate to hte poles
  4. Anaphase B
    elongation of the spindle
  5. Kinesins
    • Some move toward the plus end, others toward the minus, and some don’t move at all (depolymerases)
  6. motor proteins located along the polar microtubules
    help keep the poles apart
  7. Motor proteins on the chromosomes
    imp. in movements of the chromosomes during prometaphase, in maintaining the chromosomes at the metaphase plate, and in separating the chrmosomes during anaphase
  8. Motor proteins situated along the overlapping microtubules
    • Responsible for cross-linking antiparallel microtubules and sliding them over one another, thus elongating the spindle during anaphase B
  9. Stages in Formation of the Mitotic Spindle
    1
    • 1)      appearance of microtubules in a “sun-burst” arrangement, called an aser, around each centrosome during early prophase
    • a.       microtubules grow by addition of subunits to their plus ends, while their minus ends remain associated with the pericentriolar material (PCM) of the centrosome
    • b.      phosphorylation of proteins of the PCM by Polo-like kinase plays a key role in stimulating nucleation of spindle microtubules during prophase
  10. Stages in Formation of the Mitotic Spindle
    2
    • 1)      separation of the centrosomes from one another and their subsequent movement around the nucleus toward opposite ends of the cell carried out by increasing number of microtubules and elongation
    • a.       driven by motor proteins associated with adjacent microtubules
  11. Stages in Formation of the Mitotic Spindle
    3
    1)      the two centrosomes reach points opposite one another, thus establishing the two poles of a bipolar mitotic spindle
  12. Stages in Formation of the Mitotic Spindle
    4
    1)      after mitosis, one centrosome will be distributed to each cell
  13. Nuclear Envelope components:
    nuclear pore complexes
    disassembled as the interactions between nucleoporin subcomplexes are disrupted and the subcomplexes dissociate into the surrounding medium
  14. Nuclear Envelope components:
    nuclear lamina
    1)      nuclear lamina: disassembled by depolymerization of the lamin filaments
  15. Nuclear Envelope components:
    nuclear membranes
    1)      nuclear membranes: disrupted mechanically as holes are torn into the nuclear envelope by cytoplasmic dynein molecules associated with the outer nuclear membrane
  16. Microtubules of the Metaphase Spindle
    Astral Microtubules
    -structure and fxn
    • Structure: Radiate outward from the centrosome into the region outside the body of the spindle
    • Function: help position the spindle apparatus in the cell and may help determine the plane of cytokinesis
  17. Microtubules of the Metaphase Spindle
    chromosomal (kinetochore) Microtubules
    -structure and fxn
    • Structure: extend between the centrosome and the kinetochores of the chromosomes
    • Function:  exert a pulling force on the kinetochores, maintaining the chromosomes by a “tug-of-war”
  18. Microtubules of the Metaphase Spindle
    polar Microtubules
    -structure and fxn
    • Structure: extend from centrosome past the chromosomes; these microtubules overlap with their counterparts from the opposite centrosome
    • Function: form a structural basket that maintains the mechanical integrity of the spindle

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