Lecture 3 Overview of the cytoskeleton Microtubules, MT motors, MAPs

1. Lecture #3 Overview of the cytoskeletonMicrotubules, MT motors, MAPs

2. Figure 9.1. An overview of the structure and functions of the cytoskeleton. 

3. The Cytoskeleton is Cellular Infrastructure, much like a city plan. Highways: Filaments, the primary structural elements of the cytoskeleton Motor Cars: Motor proteins, which transport cargo along filaments Construction Crews:Remodeling proteins which allow the cytoskeleton to change shape Street Signs: Filament-binding proteins organize filaments into functional arrays.

4. Microtubules and actin filaments form the filament networks that mediate nearly all aspects of intracellular transport and cellular movement: e.g., secretion, cell motility, muscle contractility, mitosis and cell division. 

5. Function of Microtubules Establishment and maintenance of cell polarity

6. Function of microtubulesMitosis: separation of chromosomes

7. Function of microtubulesFlagellar motility

8. Microtubule structure Figure 9.10 Polymers of globular tubulin subunits (a,b dimers) g tubulin: centrosome. hollow cylinders, diameter of about 25 nm Highly polar! (+ end , � end) are variable in length, can be hundreds of ums! Singlet tubule: 13 protofilaments Doublet (A)13, (B)10 Triplet (A) 13, (B) 10, (C) 10

9. Tubulin structure are built by the assembly of dimers of a tubulin and b tubulin. Both subunits bind GTP GTP can be exchanged on b subunit

10. Microtubules have a fast and slow growing end

11. The structural cap model of dynamic instability

12. Microtubule nucleation at the centrosome Microtubule-organizing center (MTOC) Site of microtubule nucleationNote polarity of Microtubules

13. Figure 9.22 Structure of the centrosome Centrosomes contain gamma tubulin g tubulin can nucleate ab Tubulin dimers into microtubules!

14. If you inhibit mitosis, cells die.

15. Taxus brevifolia Pacific yewTAXOL (Paclitaxel) was originally collected from the bark of the pacific yew

16. Microtubules participate in a wide variety of cell activities. Most involve motion. The motion is provided by protein "motors" that use the energy of ATP to move along the microtubule

18. Figure 9.9 Molecular motors can function to transport cargo within the cell

19. There are two major groups of microtubule motors: kinesins (most of these move toward the plus end of the microtubules) and dyneins (which move toward the minus end). Some examples: The rapid transport of organelles, like vesicles and mitochondria, along the axons of neurons takes place along microtubules with their plus ends pointed toward the end of the axon. The motors are kinesins

20. Figure 9.19 Kinesin Head: binds microtubules Tail: binds cargo Kinesis is a good organelle motor. Why? It is processive!

21. Kinesin is necessary for mitosis

22. Figure 9.21 Cytoplasmic dynein.

23. Figure 9.17 Axonal transport.

24. Figure 9.7 Video microscopy enables scientists to study the biophysical properties of single molecular motor molecules

26. Properties of Tau Promotes assembly and stabilizes MTs May promote MT interactions with membranes and other cytoskeletal elements Crosslinks microtubules into bundles

28. Microtubule-Associated Proteins (MAPS) can cross-link filaments into a gel-like matrix or promote the bundling of filaments.

29. Figure 9.33 A eukaryotic flagellum. The unicellular biflagellate alga Chlamydomonas reinhardtii.

30. This electron micrograph shows the 9+2 pattern of microtubules in a single cilium seen in cross section (courtesy of Peter Satir) Each cilium (or flagellum) is made of a cylindrical array of 9 evenly-spaced microtubules, each with a partial microtubule attached to it. This gives the structure a "figure 8" appearance when view in cross section. 2 single microtubules run up through the center of the bundle, completing the so-called "9+2" pattern. The entire assembly is sheathed in a membrane that is simply an extension of the plasma membrane

31. Figure 9.34 The structure of a ciliary or flagellar axoneme.

32. Two models depicting the possible location of the key proteins in the radial spoke stalk including, LC8, calmodulin, RSP2, and RSP3 The Journal of Cell Biology,153, 2001 1315-1326Localization of Calmodulin and Dynein Light Chain LC8 in Flagellar Radial Spokes Pinfen Yanga, Dennis R. Dienerb, Joel L. Rosenbaumb, and Winfield S. Salea a Department of Cell Biology, Emory University, School of Medicine, Atlanta, Georgia 30322 b Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520

33. Figure 9.35 Longitudinal view of an axoneme.

34. The role of dynein arms in generating the force that drives ciliary or flagellar motility.

35. Figure 9.36 Basal bodies and axonemes.

36. Centrioles are built from a cylindrical array of 9 microtubules, each of which has attached to it 2 partial microtubules.

37. ������Microtubules growing in vitro from an isolated centrosome.

38. Centrosomes and Cancer Cancer cells often have more than the normal number (1 or 2 depending on the stage of the cell cycle) of centrosomes . They also are aneuploid (have abnormal numbers of chromosomes), and considering the role of centrosomes in chromosome movement, it is tempting to think that the two phenomena are related. Mutations in the tumor suppressor gene p53 seem to predispose the cell to excess replication of the centrosomes.