1. Cytoskeleton Means “cell skeleton” Internal framework of cell
Has many functions
Anchoring cell organelles
Provide cell shape
Aids in cell motility
Response to environmental signals
Comprises
Microtubules
Microfilaments
Intermediate filaments

2. Microtubules Hollow tubes made of the protein tubulin
Alternating dimers of a and b tubulin
Largest of cytoskeleton filaments
Is used for:
Maintenance of cell shape
Motility
Flagella or cilia
Movement of organelles through cell
Often involves motor molecule
Often originate from centrosome

3. 10 µm Column of tubulin dimers Tubulin dimer   25 nm Table 6-1a

4. Centrioles Located in centrosome of animal cells
Occur in perpedicular pair
Have 9 triplets of microtubules
Facilitate microtubule assembly and chromosome separation in some cells

5. Longitudinal section of one centriole Microtubules Cross section
Fig. 6-22
Centrosome
Microtubule
Centrioles
0.25 µm
Figure 6.22 Centrosome containing a pair of centrioles
Longitudinal section of one centriole
Microtubules
Cross section
of the other centriole

6. Flagellum structure
Basal body links flagellum or cilia to cell surface
Basal body looks just like a centriole
9 +2 arrangement of microtubules
Radial spokes prevent dramatic sliding and only bending

7. Cross section of cilium
Fig. 6-24
Outer microtubule doublet
Plasma membrane
0.1 µm
Dynein proteins
Central microtubule
Radial spoke
Protein cross-linking outer doublets
Microtubules
(b)
Cross section of cilium
Plasma membrane
Basal body
0.5 µm
(a)
Longitudinal section of cilium
0.1 µm
Figure 6.24 Ultrastructure of a eukaryotic flagellum or motile cilium
Triplet
(c) Cross section of basal body

8. Motor molecules Interact with tubulin or actin
Are fixed at one end and allowed to move freely at the other end
Movement is directional
Undulation-used for flagella and cilia movement
Two microtubules moving relative to one another
Organelle movement is like a ski lift tram or a monorail

9. Receptor for motor protein
Fig. 6-21
Vesicle
ATP
Receptor for motor protein
Motor protein (ATP powered)
Microtubule
of cytoskeleton
(a)
Microtubule
Vesicles
0.25 µm
Figure 6.21 Motor proteins and the cytoskeleton
(b)

10. Cell motility Cell movement facilitated by flagella or cilia
Unlike in prokaryotes, eukaryotic flagella undulate
Cilia are small appendages and they move like a swimmers arm-active stroke and return stroke

11. How cell movement works
Dynein is motor molecule that interacts with tubulin
Dynein walks along one microtubule, while bound to another
This results in bending
If no radial spokes or organelle coat, then microtubules would walk out of cell

12. Figure 6.25 How dynein “walking” moves flagella and cilia
Microtubule
doublets
ATP
Dynein
protein
(a) Effect of unrestrained dynein movement
ATP
Cross-linking proteins
inside outer doublets
Anchorage
in cell
Figure 6.25 How dynein “walking” moves flagella and cilia
(b) Effect of cross-linking proteins 1 3 2
(c) Wavelike motion

13. Microfilaments Made of two intertwined strands of actin
Helps maintain cell shape
Actin rearrangements allow engulfment events
Psuedopod formation in ameoba
Promote cytoplasmic streaming in plants
Essential for muscle contraction
Used by invading bacteria to move around cell
Frequently being assembled and disassembled within cell

14. Table 6-1b
10 µm
Table 6-1b
Actin subunit
7 nm

15. Microfilaments 2 Myosin interacts with actin to cause contraction
Cytoplasmic streaming and ameoboid motion are similar
Cortical cytoplasm around the perimiter of cell contains perpendicular actin (wind fence)
Streaming portion has parallel actin which facilitates cytoplasm movement
Plant cell wall prevents amoeboid movement of plant cell

16. Intermediate Filaments
Resemble cable in structure
Are made of protein subunits
Help maintain cell shape
Are durable and not assembled and disassembled as other cytoskeleton components
May help maintain organelle position

17. Fibrous subunit (keratins coiled together)
Table 6-1c
5 µm
Table 6-1c
Keratin proteins
Fibrous subunit (keratins
coiled together)
8–12 nm