1. Copyright © 2005 Pearson Prentice Hall, Inc. http://aimediaserver.com/studiodaily/videoplayer/?src=harvard/harvard.swf&width=640&height=520

2. Copyright © 2005 Pearson Prentice Hall, Inc. CYTOSKELETON Introduction –Movement –Structure/shape –Internal anchoring Three types of protein filaments –Intermediate –Microtubules –Actin summarized in F17-2: know – drawings & photos, diameter, protein, function, location

3. Copyright © 2005 Pearson Prentice Hall, Inc.

4. 17_02_3 types of protein filaments

5. Copyright © 2005 Pearson Prentice Hall, Inc. Intermediate filaments 10 nm Made of ropelike protein filaments Provide mechanical strength –Form meshwork –connections between cells Location: –Cytoplasmic –Nuclear Nuclear lamins F17-6

6. Copyright © 2005 Pearson Prentice Hall, Inc. Intermediate filaments

7. Copyright © 2005 Pearson Prentice Hall, Inc. Intermediate filaments

8. Copyright © 2005 Pearson Prentice Hall, Inc. Intermediate filaments Location: Nuclear Nuclear lamins F17-6 Cytoplasmic

9. Copyright © 2005 Pearson Prentice Hall, Inc. Intermediate filaments Assembly: F17-4 Monomer: a-helical w globular NH3 & COOH heads Dimer: coiled coil Tetramer: staggered anti-parallel associated pair of dimers plectin: protein that crosslinks iIFs

10. Copyright © 2005 Pearson Prentice Hall, Inc. Intermediate filaments Defects: generalization: IF defects = “blistering” of affected epithelium

11. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules 25 nm Tubulin subunits Long and straight Attached to centrosomes Microtubules Hollow Tubes w structurally Distinct Ends Dynamic assembly & disassembly

12. Copyright © 2005 Pearson Prentice Hall, Inc.

13. Microtubules Function:anchor membrane bound organelles, intracellular transport Location: cytoplasmic, but associate w chromosomes during cell division F17-9

14. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules centrosome Centrosome: at one side of nucleus - may contain a pair of centrioles contains g tubulin nucleating sites for assembly of mts F17-11 & 12

15. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules – Assembly Assembly: F17-13 maintained by balance of assembly & disassembly dimer – tightly binds GTP, hydolyzed to GDP when added to mt slow mt growth => GDP formed before next GTP dimer added, => mt disassembly

16. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules – polarize cell by selective mt stabilization F17-14 EXCELLENT ILLUSTRATION OF THE IMPORTANCE OF KA NOTE QUESTION 17-3 drugs: enhance depolymerization - colchicine

17. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules - Function anchor membrane bound organelles, intracellular transport

18. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules - Function Mechanism: movement of motor proteins along mts F17-17

19. Copyright © 2005 Pearson Prentice Hall, Inc. 17_16_Organelle_move.jpg

20. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules –motor proteins two motor proteins: kinesins move out to + enddyneins move in to – end both move by ATPase action of globular head => conformational change tail extends away from mt; binds organelle to be moved membrane bound vesicles, mitochondrion, ER, Golgi F17-23

21. Copyright © 2005 Pearson Prentice Hall, Inc. 17_19_motion_organell.jpg

22. Copyright © 2005 Pearson Prentice Hall, Inc. 17_20_microtu_gliding.jpg

23. Copyright © 2005 Pearson Prentice Hall, Inc. 17_21_single_kinesin.jpg

24. Copyright © 2005 Pearson Prentice Hall, Inc. 17_22_kinesin_moves.jpg

25. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules cilia

26. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules - Flagella

27. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules – “9 + 2”

28. Copyright © 2005 Pearson Prentice Hall, Inc. Microtubules – dynein => cilia & flagella movement

29. Copyright © 2005 Pearson Prentice Hall, Inc. 17_25_cilium_beats.jpg

30. Copyright © 2005 Pearson Prentice Hall, Inc. ACTIN MICROFILAMENTS Function –Movement –Many types: muscle cells, non- muscle cells Structure Assembly / Disassembly Interaction with other proteins Cell movement –Mechanisms –Role of actin –Role of actin-binding proteins Role of extracellular signals

31. Copyright © 2005 Pearson Prentice Hall, Inc. Actin 7 nm Globular actin subunits Twisted chains Flexible Concentrated in cortex

32. Copyright © 2005 Pearson Prentice Hall, Inc. 17_29_Actin_filaments.jpg

33. Copyright © 2005 Pearson Prentice Hall, Inc. 17_35_lamellipodium.jpg

34. Copyright © 2005 Pearson Prentice Hall, Inc. Actin Microfilament Structure G-actin vs F-actin Filament: 2-stranded helix 7 nm thin and flexible has polarity +/- ends Different binding sites –For myosin –For tropomyosin –For actin

35. Copyright © 2005 Pearson Prentice Hall, Inc. Actin Microfilament Assembly/Disassembly Grows either end, + end faster G-actin binds ATP Polymerization: G-actin ATP to ADP –Weaker bond –G-ADP promotes –depolymerization –Poisons Cytochalasins prevent polymerization Phalloidins encourage polymerization –Amanita phalloides “death cap” mushrooms Botulinum toxins prevent polymerization

36. Copyright © 2005 Pearson Prentice Hall, Inc. Actin Microfilaments Interaction with proteins Bind to G-actin –Thymosin, profilin Bind to filaments –Bundling proteins: parallel bundles of microvilli –X-linking : meshwork of cell cortex –Severing: shorten, prevent reassembly –Capping: bind to + end, prevent assembly Motor protein : myosin

37. Copyright © 2005 Pearson Prentice Hall, Inc. Actin Microfilaments Cell movement along a surface 3 Mechanisms –Form front protrusion –Anchor protrusion –Pull cytoplasm toward protrusion

38. Copyright © 2005 Pearson Prentice Hall, Inc. Actin Microfilament Actin mediates movement Formation of lamellipoda –Meshwork of actin –Membrane as sheet Formation of filopodia –Bundle of actin –Stiff protrusion

39. Copyright © 2005 Pearson Prentice Hall, Inc. 17_37_Actin_attach.jpg

40. Copyright © 2005 Pearson Prentice Hall, Inc. Actin Microfilament Role of Actin- binding proteins Nucleate filaments at leading edge membrane –Actin-related proteins (ARPs) cause branching –Capping proteins prevent disassembly –Depolymerizing protein Anchoring by integrins

41. Copyright © 2005 Pearson Prentice Hall, Inc. Actin Microfilament Motor protein: myosin Bind and hydrolyze ATP Bind to actin Move from – end to + end Structure (Type I) –Head binds actin, ATP –Tail binds membrane or vesicle

42. Copyright © 2005 Pearson Prentice Hall, Inc. 17_40_Myosin_II.jpg

43. Copyright © 2005 Pearson Prentice Hall, Inc. 17_41_slide_actin.jpg

44. Copyright © 2005 Pearson Prentice Hall, Inc. Actin Microfilament Role of extracellular signals Rho –proteins (Receptor-G proteins) –Cdc42 proteins : formation of filopodia –Rac proteins : formation of lamellipodia –Phosphoinositol pathway stimulates x- linking proteins