Final Notes 3

  1. What can produce loss of GTP cap and the pre-tubulin pool to be low so you don't have enough GTP- bound tubulin?
    • tubulin and GTP shortage
    • - microtubule will probably fall apart
    • - tubules maintained by loss and addition of dimers 
    • - w/o GTP, they fall apart
  2. Explain the dynamic instability of microtubules.
    • 1) At the + end, there is a GTP-tubulin cap. It acts as a primer for addition
    • 2) More GTP-tubulin is added to the cap, and the tubule grows. GTP-tubulin in the tubule is slowly converted to GDP-tubulin
    • 3) IF free GTP tubulin is low, more GTP-tubulin in the tubule is hydrolyzed to GDP-tubulin
    • 4) The GDP cap is unstable and the tubule depolymerizes
  3. In terms of the GTP cap, what is not needed?

    Explain the GTP cap.
    GTP energy; it doesn't take GTP energy to get them to bind together

    it promotes elongation; dimers with GTP at the end of the microtubule
  4. Why can centrioles be two different sizes in a cross section?
    When prep for microscope, making sections can cause one to chip off
  5. Explain the proximal and distal ends of the centrioles and basal bodies.

    Explain the microtubules in the centrioles and basal bodies.
    • distal end: end that centriole grows from; hollow center
    • Proximal: only at the end; cartwheel structure in middle of structure made out of protein

    • there are triplets: A is complete, B is not and neither is C
    • There have to be proteins holding the triplets

    9+0 arrangement
  6. Explain the radial spokes of the MTOCs.
    • made of alot of different proteins; at elast 17
    • - found in chlamydomonas
    • - attached to central sheath at one end and subfiber A at the other
  7. Unlike centrioles, what don't flagella and cilia have?
    have triplets; there are only two
  8. What is located in the cilia and flagella? What covers it?
    How many microtubules? Explain them.
    • axoneme
    • plasma membrane
    • doublets: there are two
    • - A is complete with all 13 subunits; B is incomplete
  9. What is coming off of microtubule A? How many?

    What are they made out of? What do they act as?
    • arms
    • two: outer (three branches to it) and inner arm (two branches)
    • arms made of dynein; when isolated, it can act as Mg-independent ATPase
    • - important in movement
  10. What comes off the subfiber B and attaches to the adjacent subfiber A?

    What projects to the center of the axoneme? Explain them.
    interdoublet links called nexin that are found at regularly spaced intervals (spacing different from dynein arms)

    radial spokes; swollen at the central end
  11. Microtubules are __ from the base to the tip. Dynein exists at __.
    Explain tectin.
    • continuous
    • regular intervals
    • present where the two subfibers meet to make sure they dont come apart; similar in structure to intermediate filament proteins
  12. What is the organization of the axoneme?
    • 9+2
    • arrangement of things in the center
  13. Structure of cilium.
    - typical pattern of the axoneme?

    - the characteristic __ of the __ has__ attached by spokes to a central cylinder. The intermediate part connects the axoneme to the __.
    9+2 pattern with the central microtubule doublet and teh ring of nine doubets linked by pairs of dynein side arms

    • cartwheel structure
    • basal body
    • triplets
    • basal body
  14. What is the distal end always connected to? 
    - What will accessory parts have to do?
    • to a cilium or flagellum
    • have to make the new structures that are in the axoneme but not in the bsaal body
  15. What occurs at the tip of the flagella or cilium (the other end)?
    capping area with plugs that fit in and prevent them from going ; it stops growth
  16. Which tubule extends firther into the tip of the cilium?

    What is the sliding-microtubule theory? Why is the contraction theory
    the A-tubuleextends further into the tip of the cilium than the b-tubule

    • - teory that predicts that the B-tubules will be missing on the outer side of the bend
    • - theory that predicts the opposite result of the sliding-microtubule theory
  17. Steps in a provisional dynein crossbridging cycle
    Steps A and B
    • a) the cycle begins with a dynein arm linked to an adjacent microtubule at the ninety degree position, the rigor position
    • b) Binding an ATP molecule from the medium causes a conformational change in the binding site at the tip of the dynein arm, so that it no longer fits the adjacent microtubule
  18. Steps in a provisional dynein crossbridging cycle
    Steps C and D
    • c) The arm releases and hydrolyzes its bound ATP, but the products of hydrolysis remain bound to the arm
    • d) hydrolysis causes a conformational change, shifting the arm to the 45 degree position and reeactivating the microtubule-binding site at its tip. In this state, the arm stores much of the energy released by ATP hydrolysis
  19. Steps in a provisional dynein crossbridging cycle
    Steps E and F
    • e) Reattachment to the adjacent microtubule releases the products of ATP hydrolysis and triggers release of the arm from its 45 degree position
    • f) the arm swivels forcefully through an arc of 45 degrees, sliding the attached microtubule along by an equivalent distance. The arm is now ready to ind a second ATp and repeat the cycle
  20. __ also move cell structures such as mito along microtubules instead of __. In this type of motility, the structure would be subbed for the bottom microtubule (in the figure). THe __ would be fixed to the structure, and the tip would do whay?
    • dynein crossbridges
    • sliding one microtubule over another
    • crossbridge base
    • move the structure along the microtubule by attaching, swiveling, and releasing from the microtubule surface
  21. Explain dynein attachment in terms of subfibers.
    dynein is attached to subfiber A and extends to the adjacen doublets B
  22. When the dynein arm is at a ninety degree angle, what does it do?

    Once it does this, what happens next?

    What happens next?

    What have the microtubules done in relation to each other?
    it binds ATP

    once bound, it loses shape, causing dynein to lose its binding part, rendering it unable to bind

    hydrolysis of ATP causing dynein to now hold ADP and a phosphate and change to a 45 degree angle position, binding to a new binding site and triggering ADP + P to leave--> back to same position

    moved relative to each other
  23. What prevents the microtubules from sliding past each other?

    If this happens on one side of the flagella, what happens?

    The subunitis that don't participate are what?
    radial spokes nad nexin links restrict how far they slide past each other

    it causes bending

    passive backsliding
  24. __ and __ have been implicated in determining where sliding occurs.

    Some sliding activity __. Other activity __. 

    __ are not involved in this at all.
    radial pokes and central sheaths

    • bends
    • beats

  25. Explain centrioles.
    • cylindrical at right angles to one another 
    • pairs
    • perpendicular arrangement
  26. Explain pericentriolar paterial
    • tubulin dimers
    • a different type of tubulin called gamma tubulin, which forms a ring where the dimers can attach
    • - area around has to contain regular dimers
    • also has paracentrin
  27. The mitotic spindle is constructed from __, each composed of __, __, and __. The __ emanating from opposite spindle poles have a __, where microtubule-associated proteins may __ them.
    • two half-spindles
    • kinetechore (chromosome), polar, astral microtubules
    • polar microtubules
    • region of overlap
    • cross-link
  28. True or False and Explain

    There are MTOCs that have no microtubules at all.

    • poles of plant spindle
    • - at pole regions are dimers, gamma tubulin, etc.
  29. What are the two possibilities of centrioles?
    no physical contact between centrioles nad microtubule of mitotic spindle

    • basal body= MTOC
    • - they connect
  30. How chromosomes migrate towards the centrosomes (the spindle poles) during anaphase A
    - They were once thought to what? 
    - In reality, what do they do?

    A kinetochore may __ and then __.
    be reeled in by the kinetochore microtubules as the microtubules shortened at their centrosome end

    the microtubules lose subunits from the kinetochore end

    actively disassemble bound microtubules and then repeatedly grasp the remaining parts of one or more shortening microtubules as if the fibers were lifelines
  31. How chromosomes migrate towards the centrosomes (the spindle poles) during anaphase A
    - It is also possible that an as yet unidentified __ is stretched between the __ and a __, in which case the microtubules might do what? 

    __ of the microtubules would then permit the elastic substance to __.
    • elastic substance
    • kinetochore
    • pole
    • restrain the elastic substance from pulling on a chromosome
    • depolymerization
    • draw the genetic material polewared
Card Set
Final Notes 3