RR Final 6 Intermediate Filaments

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  1. only identified in __. 
    animal cells

    a.       strong, flexible, ropelike fibers that provide mechanical strength to cells that are subjected to physical stress, including neurons, muscle, and epithelial
  2. a.       chemically __group of structures that are encoded by approximately __different genes
                                                                  i.      the polypeptide subunits of IFs can be divided into __based on __, as well as __, __, and __ criteria
    • heterogeneous 
    • 70
    • five major classes 
    • which type of cell they’re found in
    • biochemical, genetic, and immunologic criteria
  3. a.       radiate through the cytoplasm of a wide variety of animal cells and are often __to other cytoskeletal filaments by thin, wispy __
                                                                  i.      in many cells, these __ consist of an __ called __that can exist in numerous __
    • interconnected 
    • cross-bridges
    • cross-bridges
    • elongated dimeric protein called plectin 
    • isoforms
  4.                                                               i.      each __molecule has a bidning site for an __ at one end and, depending on the isoform, a __ for another __, __, or __ at the other end
    b.      although IF polypeptides have diverse __, all share  a similar structural organization that allows them to form similar-looking filaments
    • plectin 
    • intermediate filament
    • binding site
    • intermediate filament, microfilament, or microtubule
    • amino acid sequences
  5.                                                               i.      they contain a __ of similar length and homologous amino acid sequence
    1.       this long fibrous domain makes the subunits of intermediate filaments very different from the __ of microtubuels and microfilaments
    a.       the central fibrous domain is flanked on each side by globular domains of variable size and sequence
    • central, rod-shaped, alpha-helical domain
    • globular tubulin and actin subunits
  6.                                                                                                                                       i.      two such polypeptides spontaneously interact as their __ wrap around each other to form a __ approximately 45 nm in length
    1.       because the two polypeptides are aligned __to each other in the same orientation, the __has __, with one end defined by the __ of the polypeptides and the opposite end by their__
    • alpha-helical rods
    • ropelike dimer
    • parallel 
    • dimer 
    • polarity
    • C-termini
    •  N-termini
  7. a.       The basic building block of IF assembly is a __ formed by two __ that become aligned side by side in a staggered fashion with their__ and __ pointing in opposite (antiparallel) directions
                                                                  i.      because the dimers point in opposite directions, the __itself lacks __
    • rodlike tetramer
    • dimmers
    •  N- and C- termini
    • tetramer
    • polarity
  8. 1.     __ associate with one another in a __arrangement to form a filament that is __ in length
    a.       subsequent growth of the __ is accomplished as these unit lengths of filaments associate with one another in an __ ot form the highly elongated intermediate filament
                                                                                                                                          i.      none of these assembly steps is thought to require the direct involvement of either __ or __
    • 8 tetramers
    • side-by-side 
    • one unit
    • polymer
    • end-to-end fashion
    • ATP or GTP
  9. 1.       because the tetrameric building blocks lack __, so too does the assembled filament, which is another important feature that distinguishes Ifs from other cytoskeletal elements
    b.      What are two reasons its difficult than other types of cytoskeletal elements?
    • polarity
    • less sensitive to chemical agents
    • and more difficult to solubilized
  10.                                                                i.      treatment of a cell with ionic detergents extracts just about everything except the cell’s __
    1.       due to their __, Ifs were initially thought to be permanent, unchanging structures, so it came as a surprise to find that they behave dynamically in vivo
    a.       IF subunits are not incorporated at the ends of the filament, but rather __
    • intermediate filaments
    • insolubility
    • the interior
  11. a.       assembly and disassembly of Ifs are controlled primarily by __ and __ of the subunits
    b.      __ constitute the primary structural proteins of epithelial cells
                                                                   i.      Because of various physical connections, the IF network is able to do what?
    • phosphorylation and dephosphorylation
    • keratin filaments
    • serve as a scaffold for organizing and maintaining cellular architecture and for absorbing mechanical stresses applied by the extracellular environment
  12. a.       the cytoplasm of neurons contains __ whose long axes are oriented __to that of the nerve cell axon
                                                                   i.      these Ifs, or __, are composed of three distinct proteins: __ , __, and __

    1.       unlike the polypeptides of other Ifs, __ and __ have __ that project outward from the neurofilament
    • loosely packed bundles of intermediate filaments
    • parallel 
    • neurofilaments
    • NF-L, NF-H, and NF-M
    • NF-H and NF-M
    • sidearms
  13. a.       these sidearms are thought to do what?
                                                                                                                                           i.      in the early stages of __ when the axon is growing toward a target cell, it contains very few __ but large numbers of supporting __
    • maintain the proper spacing between the parallel neurofilaments of the axon
    • differentiation 
    • neurofilaments 
    • microtubules
  14. 1.       once the nerve cell has become fully extended, it becomes filled with __that provide __as the axon increases dramatically in diameter
                                                                 ii.      efforts to probe IF function rely on genetically engineered mice that can’t produce a particular polypeptide
    1.       studies in mice confirm the role of Ifs in imparting mechanical strength to cells situated in epithelial layers
    • neurofilaments 
    • support
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RR Final 6 Intermediate Filaments
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