1) Microtubules grow by the addition of tubulin dimers to the plus end, with polymerization favored at this end. The plus end carries a GTP cap that stabilizes the microtubule. 2) Microtubules undergo treadmilling as the GTP cap moves down the length of the microtubule until reaching the minus end, where GTP is hydrolyzed. 3) Dynamic instability occurs when a microtubule switches between growth and shrinkage, providing a source of tubulin for other microtubules. Growing microtubules are favored when GTP-tubulin concentrations are high.

2. Nucleation – the limiting step.

3. Non covalent binding of tubulin monomers

4. Dimers add to plus end of microtubule.

5. Polymerization is favored at the plus end, minus is depolymerization favored

6. Plateau phase

7. Equilibrium when dimmers add and come off equally.

8. GTP bound dimer

9. Both alpha and beta have GTP bound to them.

10. Microtubules can be stabilized.

11. Plus ends carry the GTP and they form a ‘cap’ when GTP is bound, which stabilizes the microtubule ofr a short time.

12. Cap allows growth in plus direction

13. The cap will continue to move down the length of the tubule until it reaches minus end and hydrolysis of GTP takes place.

14. Treadmilling

15. Theory of dynamic instability

16. Capping of microtubules with GTP bound dimmers, which stabilizes, but a catastrophic event can take place at the plus end, which can provide a source for tubulin for other tubules elsewhere.

17. If the GTP bound dimer concentration is high, elongation is favored, if low, then depolymerization is favored

18. Loss of cap results in GTP bound tubulin and rapid catastrophe occurs.

19. Growing end unwinds

20. Shrinkage can be stopped by increased concentration of tubulin dimers bound to GTP.

21. Provides a source of GDP dimers to be regenerated into GTP bound dimmers.

22. Shrinkage allows exchange of GDP and GTP dimers for other microtubules.

23. GEFS squeeze out GDP and then GTP is favored

24. GAPs – GTPase Activate Proteins for making GTP GDP

25. Tubulin can be an intracellular signal

26. Where are microtubules?

27. Centrosomes

28. A microtubule organizing center

29. Nerve cells have stabilized microtubules that is responsible for the orientation of them along the axon

30. Ciliated epithelial cells have basal bodies (similar to centrosomes) that attach to minus end of tubules and extend toward the apical end

31. Marginal bundle of microtubule – plus and minus are randomly assorted

32. Centrosome is made of a pair of centrioles

33. Centrioles are microtubules

34. Arranged in triplets, linked together.

35. 9 triplets make centriole

36. they contain ‘gamma-tubulin ring complex’ that make up the circular features around the peri-centriole-complex, a ton of proteins around the centrosomes to hold them. They stabilize microtubule growing filaments by binding the minus end. As long as there is enough GTP bound dimers to add on.

37. the grip proteins bind up the minus end of a microtubule, and that allows the tubule to grow rapidly at the plus end as long as there are GTP bound dimers. The grip proteins allows the orientation to take place to drive mitosis

38. Microtouble organizing centers – MTOCs

39. Nerve cells are polar w/long axons and short dendrites, so we have stabilized microtubules that have centrosomes that are responsible for the polarity. The dendrites don’t have a polarity or MTOC so the microtubules line up in opposite if not random ways.

40. Apical and basal ends, plus end at end, apical, and MTOCS attach to minus end and stabilize minus end of MT

41. Basal bodies help orient polarity of epithelial cells.

42. MT help organize the polarity of the cell

43. Motor proteins

44. Kinesin – move toward the plus end

45. Drive movement of organelles and proteins along tubules.

46. Dynein – toward the minus end

47. Drive movement of organelles and proteins along tubules.

48. Globular heads that link up to MT that requires ATP hydrolysis and a walking motion occurs. They have an ATP binding site, which specifically bind onto B tubulin subunit.

49. Light chain interacts with cargo, and heads have atp binding sites, which bind to beta tubulin subunits during movement.

50. Have different types for different cargo

51. Growth factors are taken in by receptor mediated endocytosis and can be moved by motor proteins into the cell

52. Slow and fast transport (don’t worry too much)

53. Microtoubules – slide 17

54. Important for where organelles are in the cell.

55. Tubules associate with proteins of endoplasmic reticulum and help shape/form in cytosplasm

56. Some proteins can cap the tubules and determine the structure of the cell.

57. Shape/movement are important aspects as well.

58. Polarity affects function of cell

59. MT can be capped and stabilized

60. Unstable MT can remain dynamic

61. Slide 18

62. 2 types of microubules that form outer doublet that surrounds central pair of microtubules. A and B form outer doublet.

63. Same tubules in center

64. Outer doublets are held together by stabilizing proteins, such as nexin, and the inner dynein arm, which allows outer tubule doublet to slide along one another and yet be held together to create a whip-like movement, such as cilia or cilia-like structures.

65. Slide 19

66. Linked by dynein motor proteins that bind ATP, and with ATP the motor proteins shift the microtubules in separate directions.

67. Or linking proteins that use shift of tubules, to allow the tubules to bend. When ATP is hydrolyzed, one shift ups and one shifts down for a bending, which creates movement.

68. Actin Filaments – Slide 20

69. Found just underneath plasma membrane

70. Made of actin monomers instead of tubulin monomers, such as microtubules.

71. Nucleating proteins

72. Sequestering monomer proteins

73. Bundling proteins that bind actin filaments.

74. Cross-linking proteins

75. Two actin filaments form a helical shape.

76. Polymerization of actin is bound by ATP. Actin can be bound by ATP or ADP

77. ATP: stable and addition is favored

78. ADP bound actin undergoes conformational change and associates with other actin monomers less tightly and falls off actin filament.

79. Works like tubulin, but ATP instead of GTP is involved

80. Types of Actin Filaments and associated proteins:

81. Nucleating proteins

82. Allow places for new actin filaments to grow

83. Bundling proteins

84. Bind individual actin filaments and align them so that filopodia can function

85. Filopodia are fingerlike projects at the edge of the cell. Protrude out of the membrane. Provide an ability to feel out in space and find things to take up for movement or adhesion with neighboring cells.

86. Bundling in filopodia is important for elongation.

87. Motor proteins

88. Allow for movement

89. Myosin I helps actin slide along itself

90. Capping

91. No longer polymeize

92. Cross-linking

93. Form a matrix and increase stability under plasma membrane instead of paralleling

94. Severing proteins

95. Sever actin

96. Microtubules-specific drugs

97. Phalloidin – tagged with fluorescent dyes to visualize actin filaments.

98. Used in cell cultures

99. Cytochalasin – caps filament plus

100. Taxol, colchicine – stabilize microtubules (and prevents polymerization)

101. Myosin proteins are used to stabilize actin in cells.

102. In the head, there is an actin binding domain and tail region hangs off end and regulated by other binding proteins.

103. Slide 25 – muscular cells.

104. Sarcomere will shorten as actin filaments are broguh together.

105. Cell pinching is driven by actin-myosin association.

106. Myosin-I is important for allowing actin-filament dynamics to take place at peripheral edge of membrane. Can move to distal end of cell membrane