1. Chapter 7. The Cell: Cytoskeleton

2. Modified from: Kim Foglia, Explore Biology
Cytoskeleton
Function
structural support
maintains shape of cell
provides anchorage for organelles
motility
cell locomotion
cilia, flagella, etc.
regulation
organizes structures & activities of cell
Modified from: Kim Foglia, Explore Biology

3. Modified from: Kim Foglia, Explore Biology
Cytoskeleton
Structure
network of fibers extending throughout cytoplasm
3 main protein fibers
microtubules
microfilaments
intermediate filaments
It’s a matter of size…
Modified from: Kim Foglia, Explore Biology

4. Modified from: Kim Foglia, Explore Biology

5. Evolutionary perspective
Proteins that make up the fibers are very similar in all living things
from bacteria to humans
tubulin (all cells)
actin (eukaryote cells)
Means that they are both ancient and essential for life
Modified from: Kim Foglia, Explore Biology

6. Modified from: Kim Foglia, Explore Biology
Microtubules
Structure
thickest fibers
hollow rods about 25nm in diameter
constructed of protein, tubulin
grow or shrink as more tubulin molecules are added or removed
Modified from: Kim Foglia, Explore Biology

7. Modified from: Kim Foglia, Explore Biology
Microtubules
Function
structural support & cell movement
move chromosomes during cell division
centrioles
tracks that guide motor proteins carrying organelles to their destination
motor proteins: myosin & dynein
motility
cilia
flagella
Modified from: Kim Foglia, Explore Biology

8. Modified from: Kim Foglia, Explore Biology
Centrioles
Cell division
in animal cells, pair of centrioles organize microtubules guiding chromosomes in cell division
Modified from: Kim Foglia, Explore Biology

9. Modified from: Kim Foglia, Explore Biology
Cilia & flagella
Extensions of eukaryotic cytoskeleton
Cilia = numerous & short (hair-like)
Flagella = 1-2/cell & longer (whip-like)
move unicellular & small multicellular organisms by propelling water past them
cilia sweep mucus & debris from lungs
flagellum of sperm cells
Modified from: Kim Foglia, Explore Biology

10. Modified from: Kim Foglia, Explore Biology
Cilia
Oar-like movement
alternating power & recovery strokes
generate force perpendicular to cilia’s axis
Modified from: Kim Foglia, Explore Biology

11. Modified from: Kim Foglia, Explore Biology
Flagella
undulatory movement
force generated parallel to flagellum’s axis
Modified from: Kim Foglia, Explore Biology

12. Modified from: Kim Foglia, Explore Biology
Cilia & Flagella
Structure
remember 9+2!
9 pairs of microtubules around 2 single microtubules in center
bending of cilia & flagella is driven by motor protein
dynein
Modified from: Kim Foglia, Explore Biology
requires ATP

13. Modified from: Kim Foglia, Explore Biology

14. Microfilaments (actin filaments)
Structure
thinnest class of fibers
solid rods of protein, actin
twisted double chain of actin subunits
about 7nm in diameter
Function
3-D network inside cell membrane
in muscle cells, actin filaments interact with myosin filaments to create muscle contraction
Modified from: Kim Foglia, Explore Biology

15. Microfilaments (actin filaments)
“Let’s go to the video tape!”
(play movie here)
Microfilaments (actin filaments)
Dynamic process
actin filaments constantly form & dissolve making the cytoplasm liquid or stiff during movement
movement of Amoeba
cytoplasmic streaming in plant cells
speeds distribution of materials
Modified from: Kim Foglia, Explore Biology

16. Intermediate filaments
Structure
specialized for bearing tension
built from keratin proteins
same protein as hair
intermediate in size 8-12nm
Function
hold “things” in place inside cell
more permanent fixtures of cytoskeleton
reinforce cell shape & fix organelle location
nucleus is held in place by a network of intermediate filaments
Modified from: Kim Foglia, Explore Biology

17. Modified from: Kim Foglia, Explore Biology
Summary
Microtubules
thickest
cell structure & cell motility
tubulin
Microfilaments
thinnest
internal movements within cell
actin, myosin
Intermediate filaments
intermediate
more permanent fixtures
keratin
• actin
• microtubule
• nuclei
Modified from: Kim Foglia, Explore Biology

18. Modified from: Kim Foglia, Explore Biology

19. Modified from: Kim Foglia, Explore Biology

20. Where cells touch each other…
Cell Junctions
Where cells touch each other…

21. Modified from: Kim Foglia, Explore Biology
Plant cell wall
Structure
cellulose
primary cell wall
secondary cell wall
middle lamella = sticky polysaccharides
Modified from: Kim Foglia, Explore Biology

22. Intercellular junctions
Plant cells
plasmodesmata
channels allowing cytosol to pass between cells
plasmodesmata
Modified from: Kim Foglia, Explore Biology

23. Modified from: Kim Foglia, Explore Biology
Animal cell surface
Extracellular matrix
collagen fibers in network of glycoproteins
support
adhesion
movement
regulation
Modified from: Kim Foglia, Explore Biology

24. Intercellular junctions in animals
Modified from: Kim Foglia, Explore Biology

25. Intercellular junctions
Animal cells
tight junctions
membranes of adjacent cells fused forming barrier between cells
forces material through cell membrane
gap junctions
communicating junctions
allow cytoplasmic movement between adjacent cells
desmosomes
anchoring junctions
fasten cells together in strong sheets
Modified from: Kim Foglia, Explore Biology