Study Question Sets for Exam 3
Study Question Set 18 -- Cytoskeleton & Actin - part 1

  1. Compare (a) intermediate filaments, (b) actin filaments and (c) microtubules in terms of the general pattern of distribution of each type of cytoskeletal element in an animal cell.
  2. What is the general role of "intermediate filaments" in cells? How did they get this name?
  3. Explain briefly why the subunit structure of actin filaments (and of microtubules) allows these cytoskeletal components to behave much more dynamically than intermediate filaments.
  4. What are the "+" and "-" ends of actin filaments?   What is the significance of this "+" and "-" polarity to actin filament polymerization in the cell?
  5. Describe how ATP hydrolysis after actin addition to an actin filament can affect filament elongation dynamics.
  6. Describe the effect that thymosin can have on the state of polymerization of actin filaments in non-muscle cells.
  7. Indicate the roles of profilin in facilitating or activating actin filament polymerization.
  8. What do we mean by "capping" of actin filaments?
  9. How does tropomyosin affect actin filament stability?
  10. How does cofilin affect actin filament stability?
  11. What is an "Arp"? Where does the name come from?
  12. How can Arp2/3 lead to formation of actin gels?
  13. Actin is a "highly conserved" protein. What does this mean? What types of evolutionary pressures are most probably responsible for this conservation?
  14. Describe the unit of contraction in striated muscle.
  15. What do we mean when we say that myosin in a "motor protein" for actin filaments?
  16. Compare the light chains of myosins II to those of myosins that do not form filaments.
  17. What feature makes myosin II, but not other myosins, able to form filaments?
  18. Describe the "ATPase cycle" of myosin and relate this cycle to myosin "motor" activity.
  19. What is a "minisarcomere"?
    1. What is its importance to cell phenomena such as cytokinesis (cytoplasmic division in mitosis)?
    2. Indicate other situations or locations in which one would find minisarcomeres.
  20. What are "stress fibers"?   What is the relationship between minisarcomeres and stress fibers?
  21. Indicate how calmodulin is involved in activating contraction in myosin II-based systems in non-muscle cells.

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