1. Cytoskeleton

2. 1. Maintains cell shape and support.
Roles of the Cytoskeleton
The eukaryotic cytoplasm has a set of long, thin fibers called the cytoskeleton, which plays three important roles in cellular structure and function:
1. Maintains cell shape and support.
2. Provides for various types of cell movement.
3. Helps move and organize things within the cell.

3. Cytoskeleton distribution

4. Roles of the Cytoskeleton
Cytoskeleton: Mechanical strength Structural support Internal organization Movement
Microfilaments
Intermediate filaments
Microtubules

5. Intermediate filaments
Intermediate filaments are made up of fibrous proteins that are organized into tough, ropelike assemblages (Coiled coils).
They have two major structural functions:
They stabilize cell structure.
They resist tension.
Fibrous subunit

6. Intermediate filaments
Intermediate filaments (along with desmosomes) strengthen cells against mechanical stress
Nuclear lamina
Keratin

7. Microtubules
Microtubules are long, hollow cylinders made up of many molecules of the protein tubulin.
Consists of two subunits: -tubulin and -tubulin.
Microtubules have two roles:
They form a rigid internal skeleton.
They act as a framework along which motor proteins can move and organize structures in the cell. +
End -
End  
Tubulin dimer
-Tubulin monomer
-Tubulin monomer

8. Microtubules are directional
Microtubules are directional. Often originate from a center close to the nucleus: the Centrosome
Microtubules

9. Microtubules grow and shrink constantly
Microtubule assembly
..\..\Movies\17.4-microtubule_dynamics.mov

10. Centrosome
Microtubules radiate from microtubule organizing center (MTOC)(centrosome) and function during cell division
Centrosome

11. Movement along Microtubules
Microtubules act as a framework along which motor proteins can move and organize structures in the cell.

12. Motor proteins
Motor proteins move along microtubules.
Dynein moves vesicles toward the minus end of the microtubule. Kinesin, another motor protein, moves them toward the plus end.

13. Kinesin function
Motor proteins move along microtubules.
Motor Proteins Use Energy from ATP to Move Things .
Motor proteins change their shape when energy is released from ATP.
..\..\Movies\17.5-kinesin.mov

14. Figure 4.24 Motor Proteins Use Energy from ATP to Move Things (Part 2)

15. Melanosomes movements in fish pigment cells

16. Melanosomes movements in fish pigment cells

17. Vesicular transport along microtubules
..\..\Movies\ves1.mov

18. Generating movement with microtubules
Cilia and flagella, common locomotary appendages of cells, are made of microtubules.
Flagella are typically longer than cilia, and cells that have them usually have only one or two.
Cilia are shorter and usually present in great numbers.

19. Figure 4.23 Cilia are Made up of Microtubules (Part 1)

20. Generating movement
The microtubules in cilia and flagella are arranged in a array.
At the base of each flagellum or cilium is a basal body. The nine pairs extend into the basal body.

21. Motor proteins
In both cilia and flagella, the microtubules are cross-linked by spokes of the motor protein called dynein.
Dynein changes its shape when energy is released from ATP. Many dynein molecules associate along the length of the microtubule pair.
Dynein moves vesicles toward the minus end of the microtubule. Kinesin, another motor protein, moves them toward the plus end.

22. Figure 4.24 Motor Proteins Use Energy from ATP to Move Things (Part 1)

23. Motor proteins

24. Microfilaments are made up of strands of the protein actin.
Major roles:
1. Stabilize cell shape.
2. Promote Cell movement
3.Cytoplasmic streaming
Actin monomer

25. Actin polymerization
Actin polymerization depends on ATP and monomer concentration and results in a steady state.

26. Actin binding proteins
Many proteins bind to actin filaments and modify them

27. Microfilaments for Support

28. cytoskeleton and cell movement
Myosin is a motor protein that moves along Actin filaments Myosin is organized in bundles

29. cytoskeleton and cell movement
Myosin is a motor protein that moves along Actin filaments Myosin is organized in bundles Actin and Myosin function in muscle contraction

30. Actin Filaments polymerize at the growing edge of cells.
cytoskeleton and cell movement
Actin Filaments polymerize at the growing edge of cells.

31. Actin Filaments polymerize at the growing edge of cells.
cytoskeleton and cell movement
Actin Filaments polymerize at the growing edge of cells.
..\..\Movies\Cell_Motility.mov
..\..\Movies\Actin_in_Lamellipodia.mov

32. Listeria parasites use actin to move
..\..\Movies\17.9-listeria_parasites.mov

33. Video 4.3 Tradescantia stamen hair cell
Cytoplasmic streaming
..\..\Movies\Cyt stream.mpg