cytoskeleton of cell

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

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

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. Fig. 6-21
Vesicle
ATP
Receptor for
motor protein
Microtubule
of cytoskeleton
Motor protein
(ATP powered)
(a)
Microtubule Vesicles
(b)
0.25 µm

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. Fig. 6-25
Microtubule
doublets
Dynein
protein
ATP
ATP
(a) Effect of unrestrained dynein movement
Cross-linking proteins
inside outer doublets
Anchorage
in cell
(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
Actin subunit
10 µm
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. Table 6-1c
5 µm
Keratin proteins
Fibrous subunit (keratins
coiled together)
8–12 nm