STPM Form 6 Biology Cytoskeleton

1. Cytoskeleton

2. 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

3. Made of proteins
Dynamic properties
Coordinate with each other
Coordinate with external signal

4. The cytoskeleton is composed of
networks of 3 different filaments

5. The cytoskeleton is dynamic

6. Microtubules
 Hollow tubes made of the protein tubulin
 Alternating dimers of and 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
 Spindle Fibres formation
 Cell wall formation
 Mechanical Support

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

8. Microtubules are organized to
perform specific functions

9. Maintain Cell Shape

10. Holding Organelles in Place

11. Mechanical Support

12. Microtubule structure

13. The centrosome is the primary
microtubule nucleation site in
most cells

14. Centrosome
 Microtubules
Organizing
Centre
 Hold centrioles

15. Location of Centrosome

16. Centrosomes act to polarize the
microtubule network
 Plus end - fast growing, usually in the cytoplasm
 Minus end - slow growing, anchored at the centrosome in
most cells

17. 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
 Divide during cell division

18. Fig. 6-22
Centrosome
Microtubule
Centrioles
0.25 µm
Longitudinal section Microtubules Cross section
of one centriole of the other centriole

19. Flagellum structure
 Basal body links flagellum or cilia to cell surface
 Basal body looks just like a centriole
 9 +2 arrangement of microtubules (eukaryotes)
 9+0 arrangement of microtubules (prokaryotes)
 Radial spokes prevent dramatic sliding and only bending

20. Microtubule Organization of
Flagella

21. Movement of Cillia and Flagella

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

23. Basal Body

24. Structure
 Microtubules
 Alpha & Beta Tubulin
 Microfilament
 Actin molecules

25. 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

26. Fig. 6-25
Microtubule
doublets ATP
Dynein
protein
(a) Effect of unrestrained dynein movement
ATP
Cross-linking proteins
inside outer doublets
Anchorage
in cell
(b) Effect of cross-linking proteins
1 3
2
(c) Wavelike motion

27. 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
 Cytokinesis

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

29. 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

30. 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

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