RR Final 4 Microtubules 3

  1. a.       Centrosomes are not the only MTOCs in cells   
    the  outer microtubules in a cilium or flagellum are generated as outgrowths from the microtubules in a structure called a __, which resides at the __
    1.       __ are identical in structure to centrioles, and in fact, __ and __can give rise to one another  
    • basal body
    • base of the cilium or flagellum
    • basal bodies
    • basal bodies
    • centrioles
  2. a.       __ that gives rise to flagellum of a sperm cell is derived from a centrioles that had been part of the __ of the spermatocyte from which the sperm arose
    b.      conversely, the sperm __ typically becomes a __during the first mitotic division of the fertilized egg
    2.       plants lack both centrosomes and centrioles, or any other type of obvious MTOC
    • basal body
    • meiotic spindle
    • basal body
    • centrioles
  3.                                                               i.      instead, microtubules in a plant cell are __around the surface of the nucleus and widely thoughout the __
    b.      Microtubule Nucleation
                                                                  i.      regardless of their diverse appearance, all MTOCs play similar roles in all cells: __
    • nucleated 
    • cortex
    • they control the number of microtubules, their polarity, the number of protofilaments that make up their walls, and the time and location of their assembly
  4.                                                               i.      in addition, all MTOCs share a common protein component—a type of __discovered in the late 1980s, called__
    b.      unlike the __, which are about 2.5% of the protein of a non-neural cell, __ constitutes only about 0.005% of thecell’s total protein
                                                                  i.      fluorescent antibodies to __ stain all types of __, including the __of centrosomes, suggesting that__ is a critical component in microtubule __
    • tubulin 
    •  y-tubulin
    • alpha and beta tubulins
    • y-tubulin
    • y-tubulin
    • MTOCs
    • pericentriolar material
    • y-tubulin
    • nucleation
  5. a.       insoluble fibers of the PCM are thought to serve as __ for ring-shaped structures that have the same __as microtubules and contain __
                                                                  i.      these ring-shaped structures were discovered when centrosomes were purified and incubated with __ that bound to __
    • attachment sites
    • diameter 
    • y-tubulin
    • gold-labeled antibodies
    • y-tubulin
  6. 1.       the gold particles were seen in the electron microscope to be __
    a.       these are the ends of the microtubules that are embedded in the __of the centrosome where __occurs
    2.       similar, __ have been isolated from cell extracts and shown to nucleate microtubule assembly in vitro
    • clustered in semicircles or rings situated at the minus ends of microtubules
    • PCM 
    • nucleation 
    • ytubulin ring complexes
  7. a.       Dynamic properties of microtubules
                                                                  i.      similar in __, different in __
    1.       microtubules are stabilized by the presence of__, and likely, by other factors, like __modifications to the __subunits
    a.       microtubules of the __ are __, that is, sensitive to disassembly
    • morphology
    • stability
    •  bound MAPs
    • posttranslational 
    • tubulin 
    • mitotic spindle
    • labile
  8. 1.       microtubules of mature neurons are much less __, and those of centrioles, cilia, and flagella are __
                                                                ii.      living cells can be subjected to a variety of treatments that lead to the __ without disrupting other cellular structures
    • labile
    • highly stable
    • disassembly of labile cytoskeletal microtubules
  9.                                                               i.      disassembly can be induced by __
    1.       taxol is different;what does it do
    cold temperature; hydrostatic pressure; elevated Ca2+ concentration; and a variety of chemical , like colcholine

     it binds to the microtubule polymer, inhibiting its disassembly, thereby preventing the cell from assembling new microtubular structures as required
  10.                                                               i.      the lability of cytoskeletal microtubules reflects the fact that they are __ formed by the __association of protein building blocks          
    1.       the microtubules of the cytoskeleton are normally subject to __ and __ as the requirements of the cell change from one time to another
    a.       the dynamic character of the microtubular cytoskeletaon is illustrated by plant cells
    • polymers
    • noncovalent 
    • depolymerization and repolymerization
  11.                                                                                                                                       i.      if a typical plant cell is followed from one mitotic division to the next, __ appear, one after another
    1.       during most of __, the microtubules of a plant cell are distributed widely throughout the __
    • four distinct arrays of microtubules
    • Interphase
    • cortex
  12. a.       __ is localized along the lengths of the __, suggesting that new micrtoubules might form directly on the surface of existing microtubules
    b.      once formed, the daughter microtubules are likely severed from the parent microtubule and incorporated intot eh __ htat encircle the cell 
    • y-tubulin
    • cortical microtubules
    • parallel bundles
  13. 1.       as the cell approaches mitosis, the microtubules disappear from most of the __, leaving only a single __, called the __, that encircles the cell like a belt
    a.       the __ marks the site of the future division plane
    2.       as the cell progresses into mitosis, the __ is lost and microtubules reappear in the form of the __
    • cortex
    • transverse band
    • preprophase band
    • preprophase band
    • preprophase band
    • mitotic spindle
  14. 1.       after the chromosomes separate, the mitotic spindle disappears and is replaced by a bundle of microtubules called the __, which plays a role in the __
    • phragmoplast
    • formation fo the cell wall that separates the two daughter cells
  15. these changes are accomplished by a combo of two mechanisms. What are they?
    • 1.       rearrangement of existing microtubules
    • 2.       disassembly of existing microtubules and reassembly of new ones in different regions of the cell
  16. a.       The underlying basis of microtubule dynamics
                                                                  i.      factors that influence the rates of microtubule assembly and disassembly discovered
    1.       first approach to assembly of microtubules was taken in 1972 by __
    a.       obtained __ in crude brain homogenates by adding __, __, and __ and found that microtubules are disassembled and reassembled by __
    • Richard Weisenberg
    • tubulin polymerization
    • Mg2+, GTP, and EGTA
    • lowing and raising temp
  17. a.       it is not unexpected that microtubuesl assembled in vitro might have abnormal __numbers because they lack a __ normally provided by the __ in vivo
    in vitro assembly of microtubules is aided greatly by the addition of __or by pieces of microtubules or structures that contain microtubules, which serve as templates for the addition of free subunits
    • protofilament 
    • proper template
    • y-tubulin ring complexes
    • MAPs
  18. 1.       early in vitro studies established that __is required for microtubule assembly
    a.       assembly of __ requires that a GTP molecule be bound ot the __ subunit
                                                                                                                                          i.      as it turns out, __ is not only a structural protein, it is also an enzyme; a __
    1.       __ is not required for the actual incorporation of the dimer onto the end of a microtubule
    • GTP 
    • tubulin dimmers
    • beta-tubulin
    • beta-tubulin
    • GTPase
    • GTP hydrolysis
  19. a.       rather, the __is hydrolyzed to __shortly after what, and the resulting __remains bound to the assembled polymer
    b.      after a __is released from the microtubule during disassembly and enters the soluble pool, the __ is replaced by a new __.
                                                                                                                                          i.      this nucleotide exchange “__” the dimer, allowing it to serve once again as a __ for __
    • GTP 
    • GDP 
    • the dimer is incorporated into a microtubule
    • GDP 
    • dimer 
    • GDP is relaced by a new GTP
    • recharges
    • building block
    • polymerization
  20. a.       because it includes GTP hydrolysis, assembly of a microtubule is __
                                                                                                                                          i.      when a microtubule is growing, the __ is seen under the electron microscope as an __ to which __ are added
                                                                                                                                        ii.      during times of rapid microtubule growth, __ are added more rapidly than their GTP can be hydrolyzed
    • energy expensive
    • plus end
    • open sheet
    • GTP-dimers
    • tubulin dimers
  21. 1.       the presence of a cap of __ at the __ of the __is thought to favor __ and the __                                                                                                                                    ii.      however, microtubules with __ are thought to undergo a spontaneous reaction that leads to closure of the tube, which is accompanied by the __, which generates subunits that contain __
    • tubulin-GTP dimers
    • plus ends
    • protofilaments 
    • the addition of more subunits
    • growth of the microtubue
    • open ends
    • hydrolysis of the bound GTP
    • GDP-bound tubulin
  22. 1.       GDP-tubulin subunits have a different conformation from their __ precursors and are less suited to __
    a.       the resulting mechanical strain does what?
                                                                                                                                                                                                                  i.      the strain energy is released as what happens?
    • GTP-tubulin
    • fit into a straight protofilament
    • destabilizes the microtubule
    • protofilaments curl outward from the plus end of the tubule and undergo catastrophic depolymerization
  23. 1.       thus, it would appear that __ is a fundamental component of the dynamic quality of microtubules
    a.       the __ stored in a microtubule as a result of __ makes the microtubule inherently unstable and –in the absence of other stabilizing factors suchas __—capable of disassembling soon after its formation
    b.      microtubules can shrink remarkably fast, which allows a cell to __ very rapidly
    • GTP hydrolysis
    • strain energy
    • GTP hydrolysis
    • MAPs
    • disassemble its microtubular cytoskeleton
  24.                                                                                                                                       i.      the dynamic character of the microtubular cytoskeleton inside a cell can be revealed by microinjecting labeled tubulin into a cultured cell
    1.       the labeled subunits are rapidly incorporated into the preexisting microtubules of the cytoskeleton, even in the absence of __
    a.       if individual microtubules are observed under a fluorescence microscope, they appear to __ slowly for a period of time and then __rapidly and unexpectedly
    • morphological change
    • grow
    • shrink
  25.    i.      because the switch from growth to shrinkage (called __) occurs with high frequency in vivo, most microtubules disappear from the cell in a matter of minutes and are replaced by new microtubules that grow out from the centrosome
  26. 1.       Timothy Mitchison and Marc Kirschner reported on the properties of individual microtubules and proposed that microtubule behavior in vivo could be explained by a phenomenon they termed __

    a.       __ explains the observations: (wat are the observations?
    • dynamic instability x2
    •       i.      that growing and shrinking microtubules can coexist in the same region of a cell                                                                                                                                    ii.      that a given microtubule can switch back and forth unpredictably between growing and shortening phases
  27. a.       dynamic instability is an inherent property of the microtubule itself and, more specifically, of the __ of the microtubule
                                                                                                                                          i.      it is the __ where subunits are added during growth and lost during shrinkage
    1.       this does not mean that __ cannot be influenced by external factors
    • plus end
    • plus end
    • dynamic instability
  28. a.       example: cells contain a diverse array of proteins (__) that bind to the dynamic plus ends of microtubules
                                                                                                                                                                                                                  i.      some of these __ regulate the rate of the microtubule’s growth or shrinkage or the frequency of __between the two phases
                                                                                                                                                                                                                ii.      Other __ mediate what?                                                                                                                                                                                                          iii.      once a subcellular structure is attached to the plus end of a microtubule, the __ of the microtubule can exert force on that structure
    • +TIPS
    • +TIPS
    • interconversion 
    • +TIPs
    • the attachment of the plus end of the microtubule to a specific cellular structure, such as kinetochore of a mitotic chromosome during cell division or the actin cytoskeleton of the cortex during vesicle transport

    dynaic properties
  29. 1.       __of a microtubule can push on an attached object, whereas __of a microtubule can pull on an attached object
    b.      dynamic instability provides a mechanism by which the __of microtubules can rapidly __for appropriate sites of attachment
                                                                                                                                          i.      __temporarily stabilizes microtubules and allows the cell to build the __
                                                                                                                                        ii.      __ also allows cells to respond rapidly to changing conditions that require remodeling of the microtubular cytoskeleton
    • polymerization 
    • depolymerization 
    • plus ends 
    • explore the cytoplasm 
    • attachment 
    • complex cytoskeletal networks
    • dynamic instability
Card Set
RR Final 4 Microtubules 3