Microtubule involvement in cell wall, Chemical Cycle, Mechanism of Microtubule Nucleation, GTP in

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DesLee26
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Microtubule involvement in cell wall, Chemical Cycle, Mechanism of Microtubule Nucleation, GTP in
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2013-12-04 20:01:49
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  1. Mechanism of Microtubule Nucleation
    1)      the insoluble fibers of the PCM serve as attachment sites for ring-shaped structures that have the same diameter as microtubules and contain gamma tubulin
  2. Chemical cycle
    • 1)      binding of ATP
    • 2)      hydrolysis of ATP
    • 3)      release of products (ADP and P) from the motor
    • binding of new ATP to the motor
  3. Microtubule Involvement in the Cell Wall: step one
    1)      during Interphase, most of the plant cell’s microtubules are located beneath the plasma membrane, forming a distinct cortical zone
  4. Microtubule Involvement in the Cell Wall: step two
    • 1)      The microtubules influence movement of the cellulose-synthesizing enzymes located in the plasma membrane, causing microfibrils to be assembled in an orientation parallel to underlying microtubules of the cortex
    • a.       this orientation plays role in growth characterstics and shape of cell
  5. Things that affect microtubules
    - taxol
    1)      taxol: stops the dynamic activities of microtubules by binding to the microtubule polymer, inhibiting its disassembly, thereby preventing the cell from assembling new microtubular structures as required
  6. Things that affect microtubules
    -temperature
    1)      temperature: high temperatures favor polymerization; low temperatures favor depolymerization
  7. Things that affect microtubules
    GTP
    microtubule assembly
  8. Steps in GTP participation in microtubule assembly
    a.
    a.       assembly of tubulin dimmers requires that a GTP molecule be bound to the beta-tubulin subunit (a GTP also exists in the alpha tubulin but it is permanent and can’t be exchanged), which is also a GTPase
  9. Steps in GTP participation in microtubule assembly
    b.
    b. hydrolysis is not required for actual incorporation of the dimer onto the end of a microtubule, but is hydrolyzed after the dimer is incorporated into a microtubule
  10. Steps in GTP participation in microtubule assembly
    c.
    c. after dimer is released from microtubule during disassembly and enters the soluble pool, the GDP is replaced by GTP
  11. Steps in GTP participation in microtubule assembly
    d.
    d. GTP cap at the plus end favors addition and growth
  12. Four Arrays of Microtubules in plant cells: accomplished by what?
    both rearrangement of existing microtubules and disassembly and reassembly
  13. Four Arrays of Microtubules in plant cells
    Step One
    • 1)      microtubules are distributed widely throughout the cortex; gamma tubulin, the nucleation factor, is localized along the lengths of the cortical microtubules, suggesting the formation of new microtubules directly on the surface of existing microtubules
    • once formed, the daughter microtubules are severed from the parent microtubule and incorporated into the parent buldnes that encircle the cell
  14. Four Arrays of Microtubules in plant cells
    Step Two
    1)      As the cell approaches mitosis, the microtubules disappear from most of the cortex, leaving a transverse banc, called the preprophase band, that encircles the cell like a belt
  15. Four Arrays of Microtubules in plant cells
    Step three
    1)      In mitosis, the preprophase band is lost and microtubules reappear in the form of a mitotic spindle
  16. Four Arrays of Microtubules in plant cells
    Step four
    4) After chromosome separation, the spindle disappears and is replaced by a bundle of microtubules called the phragmoplast, which plays a role in the forming of the cell wall

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