AP Biology 6.7

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!