1. Dr. Laurie Solis
AP Biology 6.7

2. Extra cellular components and connections between cells help coordinate cellular activities.

3. Cell Walls of Plants
Cell walls are an ‘extra cellular’ structure of plant cells that distinguishes them from animal cells

4. Cell walls Protects the plant cell Maintains the cells shape
Prevents excessive uptake of water
On the whole the cell wall holds up the plant against the forces of gravity

5. The story of the cell wall…
Once upon a time…
There was a baby plant…
A young plant cell first secretes a relatively thin and flexible wall called the ‘primary cell wall’

6. The story of the cell wall…
In actively growing cells, the cellulose fibrils are oriented at ‘right angles’ to the direction of cell expansion
This affects the growth pattern and can be seen under a microscope.

7. Cell wall…
As a result, it is believed microtubules in the cell cortex guide cellulose and deposits the fibrils
The cellulose is oriented in the way of growth
Thereby, microtubules affect the growth pattern.

8. Cytoskeleton The cytoskeleton is both a: muscle and a skeleton,
and is responsible for
cell movement,
cytokinesis,
and the organization of the organelles within the cell.

9. Middle Lamella Middle lamella
Thin layer rich in sticky polysaccharides called pectins
Located between primary walls of adjacent cells
This glues adjacent cells together
When the cell matures and stops growing it strengthens its wall

10. Middle Lamella Middle lamella
The glue the middle lamella uses is called: pectin
Pectin is used as a thickening agent in jams and jellies

11. Secondary wall Some plant cells have a secondary wall
Deposited between the plasma membrane and the primary wall
Deposited in several layers
Strong and durable matrix
Strong cell protection and support
Wood is composed mainly of secondary layers

12. Extracellular Matrix-Animal Cells
Animal cells do not have cell walls
Instead, they have an extracellular matrix (ECM)

13. ECM ECM Main ingredients are: Glycoproteins secreted by the cell
Glycoproteins are proteins with covalently bonded carbohydrates, usually short chains of sugars

14. ECM There are different types of glycoproteins
The most common in animal cells is collagen
Collagen forms strong fibers outside of the cell
Collagen accounts for 50% of the total protein in the human body!

15. Collagen
Because collagen is fibrous it is embedded in a woven web from proteoglycans
Proteoglycans consist of a core protein with many carbohydrate chains attached.
Often it is 95% carbohydrate

16. ECM-Fibroconectin/Integrin
Fibroconectin is also part of the ECM
Binds (and other proteins) to surface receptor proteins of the cell called integrins (inside the plasma membrane)
Integrin transmits signals between the ECM and the cytoskeleton and integrate changes occurring outside and inside the cell

17. ECM research
New research on the ECM indicates that the role of the ECM, fibroconectins and integrins affect what goes on in the cell

18. Cells – collective operation
Even though we look at cells individually, remember that:
Cells act collectively
Cells make up tissue, organs, and organisms
Cells interact, adhere, and communicate through direct physical contact

19. Cell Walls - Plasmodesmata
So far we’ve learned that plant cells have a strong exterior wall
However, cell walls are perforated with channels called plasmodesmata

20. Cell Walls - Plasmodesmata
Plasmodesmata, allows cytosol to pass through so it can connect the physical environments of the adjacent cells
Plasma membranes line each channel
Water and small solutes can pass easily through

21. Animal Cells/Junctions
Animal cells have three types of intercellular junctions
Tight junctions
Desmosomes
And gap junctioins
Occur in the epithelial tissue (external and internal surfaces of the body)

22. Animal Cells/Junctions
Tight Junction
Plasma membranes are tightly pressed together
Bound by specific proteins
Form continuous seals
Tight seal, prevents leakages of cellular fluid (that is why sweat leaks out of our body and not into another cell)

23. Animal Cells/Junctions
Desmosomes
Function like rivets, and fasten cells together in strong sheets
Contains filaments made of keratin proteins
Creates tissue and muscle!
Muscle tears are really tears in desmosomes!

24. Animal Cells/Junctions
Gap junctions
Provide cytoplasmic channels from one cell to an adjacent cell
Contain membrane proteins
Necessary for communication between cells

25. Conclusion – Cells are integrated
Remember that
Cells are integrated!
That means they work together!
The cell is a living unit greater than the sum of its parts!