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AP Biology 6.7

Dr. Laurie Solis. AP Biology 6.7. Extra cellular components and connections between cells help coordinate cellular activities. Cell Walls of Plants. Cell walls are an ‘extra cellular’ structure of plant cells that distinguishes them from animal cells. Cell walls. Protects the plant cell

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AP Biology 6.7

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  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!

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