2. The Cytoskeleton Functions
Organize Cells in space and supports the fragile plasma membrane
Cell movements
Drives and guides the intracellular traffic of organelles
Chromosomes division at mitosis

3. Three Types of Filaments
The cytosol of a eukaryotic cell contains three types of filaments that can be distinguished on the bases of their
Diameter
Type of subunit
Subunit arrangement
Actin filaments, also called microfilaments
Microtubules
Intermediate filaments (IFs)
Regulation of the dynamic behavior and assembly of the cytoskeletal filaments allows eukaryotic cells to build an enormous range of structures from the three basic filament systems

6. Actin Filaments
7–9 nm in diameter and have a twisted two-stranded structure
Monomeric actin subunits assemble into microfilaments
Determine the shape of the cell's surface and are necessary for whole-cell locomotion

7. Actin Structural and Functional Polarity
one end of the filament is favored for the addition of actin subunits and is designated the ( +) end, whereas the other end is favored for subunit dissociation, designated the (-) end

8. Microfilament-based Structures

9. Actin Cross-linking Proteins

10. Actin Cross-linking Proteins

11. Actin-Myosin powered movment

12. the erythrocyte membrane showing the spoke and-hub organization of the cytoskeleton
Band 4.1  elliptocytosis or spherocytosis , also band 3 and spectrin

13. the erythrocyte membrane showing the spoke and-hub organization of the cytoskeleton

14. Microtubules Hollow tubelike structures, 24 nm in diameter
Their walls are formed by adjacent protofilaments
Dimeric subunits composed of α and β tubulin
Determine the positions of membrane-enclosed organelles and direct intracellular transport
13 laterally associated
Protofilaments
+ end beta is exposed

17. Microtubules Radiate from Centrosomes
Microtubules are not randomly distributed in cells.
They radiate from the centrosome, which is the primary microtubule-organizing center (MTOC) in animal cells
In many nondividing animal cells, the MTOC is located at the center of the cell near the nucleus
In most cases the (-) end of the microtubule stays anchored in the MTOC while the ( +) end extends away from it.

23. Microtubule-Based Motor Proteins

24. Intermediate Filaments
Have the structure of a 10 nm diameter rope
Intermediate filaments are assembled from a large diverse family of proteins.
The most common intermediate filaments, found in the nucleus, are composed of lamins
Provide mechanical strength

25. Intermediate Filaments
Intermediate filaments constructed from other proteins are expressed preferentially in certain tissues: for example,
keratin-containing filaments in epithelial cells
desmin-containing filaments in muscle cells
Vimentin containing filaments in mesenchymal cells

26. Fluorescence micrograph of a PtK2
fibroblast cell stained to reveal keratin intermediate
filaments

27. The formation of protein filaments from much smaller protein subunits allows
regulated filament assembly and disassembly to reshape the cytoskeleton
weak noncovalent interactions hold together the three types of cytoskeletal "polymers"

29. Distribution of Cytoskeletal Filaments
Cytoskeletal filaments, often concentrated in distinct locations
In absorptive epithelial cells, actin filaments (red) are
concentrated in the apical region and in a narrow band in the
basolateral region. Microtubules (blue) are oriented with the long
axis of the cell, and intermediate filaments (green) are
concentrated along the cell periphery especially at specialized
junctions with neighboring cells and lining the nuclear
membrane.

30. Organization of the cytoskeleton in polarized epithelial cells.

31. Cytoskeleton Evolution
The cytoskeleton has been highly conserved in evolution.
only a small percentage of differences in sequence between yeast and human actin and tubulin
The absence of IF-like proteins in bacteria and unicellular eukaryotes is evidence that intermediate filaments appeared later in the evolution of the cytoskeletal system.
The first IF protein to arise was most likely a nuclear lamin from which cytosolic IF proteins later evolved.