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36 Cards in this Set
- Front
- Back
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What 3 filaments is the cytoskeleton composed of?
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1. actin filaments (microfilaments)
2. intermediate filaments 3. microtubules |
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Actin filaments
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2-stranded helical polymers
diameter of 2 chains of actin: 5- 9nm |
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Intermediate filaments
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10nm diameter
one type forms nuclear lamina some give mechanical strength not all cells have |
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Microtubules
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long, hollow tubes made of tubulin
attached to MTOC 25 nm outer diameter a & b-tubulin dimers assemble into microtubule |
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Formation of cytoskeletal filaments
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- cytoskeletal filaments held together by many weak noncovalent interactions
- small protein subunits assemble into protofilaments - protofilaments form larger filaments - this method of formation allows for more flexibility and stability |
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Types of intermediate filaments
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- nuclear
- vimentin-like - epithelial - axonal |
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Component polypeptides & location of nuclear IF
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lamins A, B, and C
nuclear lamina |
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Component polypeptides & location of vimentin-like IF
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vimentin
cells of mesenchymal origin |
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Component polypeptides & location of epithelial IF
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type I keratins (acidic) & type II keratins (basic)
epithelial cells & their derivatives |
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Component polypeptides & location of axonal IF
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neurofilament proteins
neurons |
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____ & ______ assemble into a polarized/directional structure
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Microtubules and actin.
two ends polymerize at different rates + end grows faster difference in growth rates at the two ends is made possible by changes in the conformation of each subunit as it enters the polymer |
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Actin and tubulin are enzymes
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Actin binds and hydrolyzes ATP.
a-b tubulin binds 2 GTPs, but only b hydrolyzes GTP. Free monomers are NTP-bound; subunits in polymer are NDP-bound NDP has less affinity than NTP for the polymer |
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Microtubule dynamic instability
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Microtubules depolymerize about 100 times faster from an end containing GDP tubulin than from one containing GTP tubulin.
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Nucleation is the rate-limiting step
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For actin assembly
Concentration dependent |
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Treadmilling
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Fiber length remains the same
NTP added to + end NDP removed from - end |
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Actin-specific drugs
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Phalloidin - binds/stabilizes filaments
Cytochalasin - caps filament plus ends Swinholide - severs filaments Latrunculin - prevents subunit polymerization |
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Microtubule-specific drugs
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Taxol - binds/stabilzes microtubules
Colchicine - prevents subunit polymerization Vinblastine - prevents subunit polymerization Nocodazole - prevents subunit polymerization |
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FtsZ
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Filament forming protein in E. coli
Similar to tubulin Forms rings at the point of cell division during the bacterial cell cycle |
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Microtubule Organization Center (MTOC)
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Aka "centrisome"
Where all microtubules originate Centrioles - specialized, short microtubule structures Centrioles are surrounded by a fibrous network of gamma-tubulin ring complex (y-TuRC) y-TuRC: initiates microtubules, nucleates polymerization of tubulin |
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Actin arrays
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Initiated at the Arp 2/3 complex (Arp = actin related proteins)
Usually nucleated at the plasma membrane Actin web formation is nucleated by the Arp complex Arp 2/3 complex can bind the sides of existing actin filaments, forming branches at 70 deg |
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_____ can bind to free monomers or polymers.
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regulatory proteins
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Types of regulatory proteins: actin, monomer binding
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thymosin, profilin
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Types of regulatory proteins: actin, filament binding
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destabilizing: cofilin
severing: gelsolin capping: CapZ(+ end), tropomodulin (- end) filament crosslinking proteins -form actin bundles: fimbrin, a-actinin, villin -form actin webs: spectrin, filamin |
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Types of regulatory proteins: microtubule, monomer binding
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Stathmin
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Types of regulatory proteins: microtubule, filament binding
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Stabilizers
-MAPs, microtubule associated proteins (MAP2, Tau) Destabilizers -catastrophin -katanin (ATPase) |
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_______ stabilizes microtubules while _____ promotes depolymerization
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MAPs stabilize; catastrophin depolymerizes
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Different actin crosslinks are used for different structures. What structures do they form, and what dictates which structures are formed?
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Contractile bundles, gel-like networks, tight parallel bundles
Depends on actin cross-linking proteins |
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Actin filaments + alpha-actinin
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Loose packing allows myosin II to enter bundle
Contractile bundle |
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Actin filaments + fimbrin
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Tight packing prevents myosin II from entering bundle
Parallel bundle |
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___ promotes a gel-like actin state
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Filamin
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Catastrophe
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Microtubules shrink due to loss of GTP cap (microtubule dynamic instability)
GTP was hydrolyzed to GDP, which causes the beta subunit to curve |
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cofilin
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actin, filament-binding regulatory protein
destabilizing |
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gelsolin
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actin, filament-binding regulatory protein
severing |
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CapZ
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actin, filament-binding regulatory protein
capping (+ end) |
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tropomodulin
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actin, filament-binding regulatory protein
capping (- end) |
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Actin filament cross-linking proteins
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form actin bundles:
fimbrin, a-actinin, villin form actin webs: spectrin, filamin |
