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44 Cards in this Set
- Front
- Back
3 main types of major filaments
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actin, micrtubules, intermediate filaments
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function of actin filaments
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cytoplasmic streaming,
provide mechanical strength to a cell by forming a band under the plasma membrane generte locomotion in cells |
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functions of microtubules
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They determine the positions of
membrane-enclosed organelles and direct intracellular transport |
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intermediate filaments provide
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mechanical strength
depend on lateral budnling and coiled coils |
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tubulin actin molecules assemble
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head to tail to create polar filamentst
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tubulin is a
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heterodimer
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what is the rate limiting step in formation of a cytoskeleton polymer
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nucleation
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filament treadmilling and dynamic instabilty are
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consequences of nucleotide hydrolysis by tubulin and actin
as filament grows, elongation is faster than hydrolysis at the plus end and the terminal subunits are always in T form. at minus end its vice versa in d form |
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treadmilling occurs
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at intermediate concentrations of free subunits
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actin molecules nucleate at the
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plasma membrane
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actin elongation is regulated by
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formins
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how are actin filaments organzed
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by crosslinking proteins
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A protein complex containing γ-tubulin nucleate
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microtubules
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Microtubules emanate from the
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centrosome in animal cells
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Stathmin binds to two tubulin heterodimers and
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prevents their addition to
the ends of microtubules. |
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t/f the role of ATP hydolysis in actin polymerization is simlar to the role of GTP hydrlys
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true
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t/f in most animal cells, minus end directed microtuble motors deliver their cargo the peryphery of the cel
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flase
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t/f motor neyrons triffer action potentials in cell membanes that open voltage sensitve in t
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flase
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how does lateral association promote the subsequent rapid formation of a microtubule
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once first association has occured, th enext alpha beta dimer can bind much more readily because its stabilized by lateral and longitudnal contact
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how many alpha beta tubulin dimers are added to the ends of a microtubule each second
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54 per second
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how does a centrosome know when its found the center of the cell
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it nucleates a 3d array of microtubes that grow until they encounter an obstacle, the plasma membrane. dynamic nstability of microtubules plus equal pushing in each direction eventually lead it to the center. when alll oppositely directed microtubles are the same length, its in the center
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the concentration of actin in cells is 50-100 times grater han the critical condition ovserved for pure actine in a test tube. how is this possible
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in cells, most of the actin subunits are bound to thymosin, which locks actin in a form that cant hydrolyze its boudn atp and cant be added to filament ends. thymosin reduces concentration o ffree actin to around the critical cocenctraion. Advantage is that the cell can maintain a large pool of subunits for explosive growth at the sites and times of its choosng.
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what is a tubulin homolog in bacteria
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FTSZ
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intermediate filaments
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example: nucelar lamins
subunits are fibrous elongated, not globular |
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ARP complex of actin grows from the
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negative end, allowing elongation at the positve end
proteins that play a role:Arp 2 and Arp3 works best when attached at a 70 degree angle |
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formin
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dimer. Associates with the plus end. Binds to actin subunit and elongates filament only through the + end
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thymosin
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locks actin so that it cannot bind to the positve or negative end
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proflin
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associates with plasma membrane and recruits actin monomers
it binds to the site opposite of actin binding site |
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tropomysosin
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stabilizes
has 7 actin filaments filaments by binding simultaneously to seven adjacent actin subunits in one protofilament This prevents other proteins from binding to actin |
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cofolin
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destabilizes by forcing a really tight twist
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Stathmin of microtubules
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binds the two heterodimers so they are not available for growth. When microtubules need to grow, phosphorylate stathmin and release microtubules
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dyneins
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family of minus end directed microtubules
2 tyoes: cytoplasmic dyneins and axonemal dyneins cytoplasmic found in eucaryotes for vesicle transportation |
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t/f the structural polarity of all microtubules is taht alpha is exposed at one end and beta exposed at the other
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true
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t/f like actin filaments and microtubules, cytoplasmic intermediate filaments are found in all eurcaryotic cells
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false
only in metozoans |
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what are the general functions of intermdiate filaments, acin, and microtubules
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intermediate filaments: mechanical stability
actin: determine cell shape and are required for locomotion microtubules: direct intracellular transport and determine position of organelles |
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why are humans strong if connections weak?
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large number of filaments so stress is spread out so their interaction strength will not be exceeded
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lag phase
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actin monomers assmeble into a nucleus for polumerization
B- is formation of a nucleas/rapid growth C-equilibrium between rates of addition and release of actin |
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why does a microtubule shrink
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it lost its GTP cap
if you add enough GTP subunits, you can stop shrinking |
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what is GAP for beta tubulin
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tubulin itself, it accelerates GTP hydrolysis by the formation of intersubunit contacts during polymer- ization.
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few examples of the differences between bacteria and animal cells
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Animal cells are much larger, diversely shaped, and do not have a cell
wall. Cytoskeletal elements are required to provide mechanical strength and shape in the absence of a cell wall. Animal cells have internal organelles. Animal cells, and all other eucaryotic cells, have a nucleus that is shaped and held in place by intermediate filaments |
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disulfide bonds do not form in cytosol of eucaryotic cells yet keratin intermediate filaments in skin are corsslinked by disulfide bonds. How can this be?
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these bonds form after the cell has died
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why are these drugs toxic to dividing cells?
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Cell division depends on ability of microtubules to polymerize and depolymerize. Taxol- treated cells are prevented from depolymerizing their existing microtubules, and thus cannot form a mitotic spindle. Colchicine-treated cells cannot polymerize new microtubules, and thus are also prevented from forming a mitotic spindle.
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is acrylamide toxicity mediated through its effects on neurofilaments?
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probably notIf the original hypothesis were correct, then acrylamide toxicity would have been expected to be absent in mice that are missing neurofila- ments.
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how does cofolin distinguish old from new
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older has more ADP actin
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