Microtubules, IMF, MF

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Microtubules, IMF, MF
2012-08-27 21:18:14
Sickles Hill

Med School
Show Answers:

  1. Three types of filaments with diameters?
    MF (5-7nm) < IF (9-11nm) < MT (25nm) 
  2. Protein composition of the three filaments?
    MF = actin, MT = tubulin, IF = tissue specific subunits (i.e. epithelial tissues = keratin)
  3. Rank MF, IF, MT in terms of the amount of associated proteins. 
    MF > MT > IF
  4. Which are types of proteins are globular and which are filamentous?
    MF, MT = globular; IF = filamentous
  5. Rank the order of these proteins in terms of their subunit interactions to maintain stiffness?
    IF > MT > MF
  6. Match physical properties to the right protein:

    Similar to thick cables (resist tensile forces)
    Stiff tubles (push and pull)
    Railway system for intracellular transport
    Bundle for strength/cross-link into networks
    IF: similar to thich cables

    MT: railway system, stiff tubes able to push and pull

    MF: bundle for strength, x-link into networks
  7. Which proteins as vastly polymers and which are 50:50 monomer:polymer?
    IF: mainly polymers; MF,MT are 50:50 monomer:polymer
  8. Characteristics of tubulin?
    • Learning Slide:
    • alpha-beta dimer (beta is positive end)
    • highly conserved (any change in AA seq. will mess it up)
    • important protein (10-20% of total soluble protein in brain)
    • Beta subunit can carry GTP
  9. What is MTOC?
    aka centrosome (centroile + gamma-tubulin)

    Gamma-tubulin nucleates formation of MT (plus end away from MTOC)

    Some MT have no identifiable MTOC (i.e. neurons)
  10. Dynamic Instability?
    MT constantly scanning cytoplasm and changing length (slow assembly and catastrophic disassembly)
  11. How does dynamic instability work?
    Growing: GTP tubulin molecules add to the MT faster than GTP hydrolysis.

    Shrinking: protofilaments with GDP tubulin peel away because of curved shape (weak bonds)

    • If GTP addition > rate of hydrolysis = GTP cap (growing)
    • If GTP addition < rate of hydrolysis = GDP cap (disassembly)
  12. Cytoplasmic microtubules (polarity and type)?
    single MTs radiating from MTOC; Negative end at the MTOC
  13. Neuronal MTs polarity (axonal and dendritic)
    • Axonal: plus end away from cell
    • Dendritic: mixed polarity
  14. Mitotic MTs polarity?
    Double aster (centrosomes or MTOCs) of MTs with minus ends at the spindle poles
  15. Definition of Axoneme? 2 Examples of Axoneme? 
    • 9+2 MT structure (9 outer MT doublets and 2 single central MTs) for a total of 20 MTs
    • Respiratory Cilia and Sperm Flagellum
  16. 2 Examples of MT triplets?
    • Centrioles and Basal Bodies (body of cilia & flagellum)
    • 9 Sets of triplet MT (i.e. 27 MTs)
  17. Stability of Cytoplasmic MT, Mitotic MT, Neuronal MT, Axonemal MT, and Centriole, Basal Bodies?
    All stabile except for Mitotic Spindle and Cytoplasmic MT

    • Mitotic Spindle: very dynamic (half-life of 15 seconds)
    • Cytoplasmic MT: half-life of 10 minutes
  18. Which MT-associated proteins (MAPs) are spatially regulated?
    • Tau- found only in axon
    • MAP2 - found only in neuron dendrites and cell body

    **Phosphorylation of MAP decreases their affinity for MT, decreasing stability (bc MAP generally increase stability)
  19. Stathmin?
    curved MAP that prevents assembly of tubulin
  20. Kinesin-13?
    Rips tubulin from (+) ends of MT
  21. Katanin?
    Severs MT (like a sword)
  22. TIPs?
    Caps MT and makes them stable; attaches to membranes
  23. Plectin?
    Links/Binds MT to intermediate filaments (IF)
  24. Kinesin motor protein is ____ bound.
    Dynein motor protein is _____ bound. 
    • Kinesin is (+) oriented (outward transport)
    • Dynein is (-) oriented (inward transport)
  25. Positioning of organelles: Mitochondria, ER, Golgi, and MT-dependent IMF use which motor proteins?
    Mito- Kinesin and Dynein

    • ER - Kinesin
    • MT-dependent IMF - Kinesin

    Golgi - Dynein
  26. Nexin?
    Protein linking adjacent "outer" doublets of cilia internal structure 
  27. Mechanism of cilia/flagellum movement?
    Nexin links convert sliding of dynein motor proteins into bending 
  28. Minus directed Kinesin that aligns MT during spindle formation?
  29. Plus-end directed, tetrameric kinesin that seperates centrosomes?
  30. Mechanism of seperating chromosomes?
    Kinesin-14 aligns MT, kinesin-5 seperates centromeres, and dyneins near cell membrane "pull" centrosomes (MTOC, or aster) towards them.

  31. Anaphase A vs. B?
    Anaphase A: disassembly of kinetochore MT

    Anaphase B: tetrameric kinesins slide polar MT apart and membrane bound dyneins pull aster MTs towards membrane
  32. MT related drugs can be carcinogens how? Why are they a good target for cancer treatment?
    At low doses; involved with every phase of mitosis/meiosis
  33. Colchicine?
    truncates the assembly process of MTs, but disassembly can still occur....net result = disassembly
  34. Vinca alkaloids?
    doesn't allow tubulin to form MT by precipitating tubulin (no assembly)
  35. Taxol?
    Doesn't let MT breakdown/disassemble (i.e. hyperstabilizes MTs)
  36. Chemotherapy best target the most ____ MT which are mitotic of cytoplasmic MT?
    dynamic; mitotic (half-life is really short)
  37. Three categories of actin?
    4 muscle isoforms: alpha (skeletal muscle, cardiac, visceral and cascular smooth muscle)

    • 2 non-muscle isoforms: 
    • Beta-cytoplastic = cell cortex (cell structure)
    • Gamma-cytoplastic = stress fibers
  38. Monomeric actin is globular or filamentous? polymer? Is it polar? ATPase?
    • Monomeric: globular, polar, ATPase
    • Polymer: filamentous, polar
  39. Assembly dynamics of actin?
    • The arrow tip is (-) end, and back is (+) end
  40. Actin sequestering proteins?
    • Profilin = like GEF, adds ATP where ADP was
    • Cofilin +Thymosin = both block release of ADP and dont let polymer grow
  41. Nucleation complexes are needed for assembly. Examples include?
    Arp 2/3 (helps actin branch off), tandem, and formin
  42. Stress fibers/cytosolic actin/migrating cells vs. microvilli, muscle, non-migrators
    dyanamic vs. stable
  43. Actin stabilizing molecules (tropomyosin)?
    Doesn't let ADP release; doesn't let other molecule (sever molecules bind)
  44. Actin severing molecules (Gelsolin, Cofilin)?
    Gelsolin + Cofilin sever actin and cap + end to inhibit growth but Cofilin also rips loose the (-) end
  45. Actin example of motor protein?
  46. Rho family GTPases of actin?
    control actin assembly/disassembly via phosphorylating/dephosphorylating
  47. Listeria is a ____ infection that uses actin to _____ and hide from ___.
    bacterial infection; actin; immune system
  48. Phalloidin (from actin lecture) is similar to ____ (from MT lecture) because it _____.
    Taxol; hyperstabilizes actin (doesnt allow it from disassembling)
  49. Cytochalasin infection (actin lecture)?
    Block polymerization
  50. What is the function of spectrin? Characteristics of spectrin?
    Spectrin keeps cell membrane integrity. Contains binding domains at end and spacers inbetween. 

    **binding domain mutations are SEVERE (i.e. Duchenne's Muscular dystrophy)
  51. Diseases related to spectrin? 
    Hemolytic anemias:

    1. Spherocytosis: pinching off of the RBCs (ankyrin binding domain messed up)

    2. Elliptocytosis: RBCs lyse to due messed up spectrin
  52. Two types of muscular dystrophy? Differences?
    Duchenne's MD: premature stop codon; actin binding domain mutation

    Becker's MD: spacer domain repreats of spectrin
  53. 6 types of intermediate filaments?
    • Type I and II: Keratins (found in epithelial cells)
    • Type III: Desmin (muscle), GFAP (glia), and Vimentin (mesenchymal, endothelial, etc.)
    • Type IV: Neurofilaments (neurons)
    • Type V: Nuclear lamins
    • Type VI: Lens fibers
  54. The IF subunits are nonpolar or polar, linear or globular?
    subunits are linear and polar
  55. IF assembly consists of?
    parallel dimers (polar), tetramers (anti-parallel [non-polar] = unit-length filament)
  56. Growing assembly of IF (from subunit to IF)?
    Dimer, tetramer, ULF, linear end-on-end addition ofULF (non-polar)
  57. ULF have the intrinsic ability to repair themselves?
  58. Phosphorylation of the head =?
    Phorphorylation of the tail =?
    • Phosphoryl. of the head = disassembly
    • Phosphoryl. of the tail = creation of side arms 
  59. Function of tonofilaments?
    link cells together to transfer mechanical force
  60. Keratin mutations?
    K5 or 14, basal layer mutation leads to epidermolysis bullosa simplex (EBS)

    K1, or 10, stratum spinosum mutation leads to epidermolysis hyperkeratosis (EH)
  61. Desmin mutation?
    Increased susceptibility to muscle damage (dystrophies)
  62. Lamin A laminopathy?
    Hutchinson-Gilford progeria