The Plasma (Cell) Membrane

1. The Plasma (Cell) Membrane The Fluid Mosaic Model

2. TEM view of thePlasma Membrane

3. Function of the Plasma Membrane • A “selectively” or “semi” permeable membrane that restricts the movement of various molecules into and out of the cell. • Allows for communication between cells. • Provides the cell with a specific “marker” that tells all of the other cells who it is.

4. Membrane Composition 1. Phospholipid molecules: * make up most of the cell membrane * provides a barrier between cytoplasm & outside the cell • Carrier proteins: * used to move molecules across the membrane * some require energy others do not • Glycoproteins/ Glycolipids: * used as cell markers

5. Phospholipids • Hydrophilic(loves H2O ) head represents the PHOSPHO part of the molecule. • Hydrophobic(hates H2O ) tail represents the LIPID part of the molecule. • Outside & inside the cell there’s a lot of H2O , therefore the hydrophilic part is in contact with H2O but the hydrophobic part is as far away as possible from H2O.

6. Carrier Protein • Passive Channel: *Leakage channel *Requires no cellular energy • Active Channel: * Open and close to let larger molecules through * Uses Cellular energy (ATP)

8. Cell Membrane Outside of cell Glycoproteins Proteins Cell membrane Protein channel Phospholipid Bilayer

9. Plasma (Cell) Membrane • Animation # 1 • Animation # 2

10. Moving Materials Across The Cell Membrane Two ways : 1. Passive Transport (PT) Requires no cellular energy 2. Active Transport (AT) Requires cellular energy (ATP)

11. Particle Theory • 1. All matter is made of particles • 2. The particles are in constant motion (Kinetic motion of particles) • 3. The closer the particles are together, the greater the attractiveness between them.

12. Particle Theory • Solids: definite shape and volume • Liquids: definite volume but indefinite shape • Gases: indefinite shape and volume • Matter

13. Three Types of PT 1. Diffusion • Osmosis 3. Facilitated Diffusion

14. Diffusion • Molecules move from an area of high concentration [ ] to an area of low [ ] until Equilibrium is reached where [ ] levels are equal. • Small molecules like O2 and CO2 can diffuse across the plasma membrane. Large molecules (ex. Glucose) or ions (an ion is a charged particle) can’t pass through by diffusion.

15. Osmosis • Special type of diffusion involving water passing through a selectively permeable membrane. • Water always move from an area of high [ ] to an area of low [ ].

16. How Osmosis Works Dilute sugar solution (Water more concentrated) Concentrated sugar solution (Water less concentrated) Sugar molecules Movement of water Selectively permeable membrane

17. Osmosis & Cellular Environments Hypotonic: water [ ] outside cell is greater than water [ ] inside cell. Hypertonic: water [ ] outside is less than water [ ] inside. Isotonic: water [ ] outside equals water [ ] inside.

18. Animal Cell Hypotonic Solution high H2O [ ] outside , H2O flows into cell , pressure builds up , cell bursts which is called cytolysis.

19. Animal Cell Hypertonic Solution low H2O [ ] outside , H2O flows out of cell pressure drops , cell becomes dehydrated and shrivels up.

20. Animal Cell Isotonic Solution The H2O [ ] outside the cell equals the H2O [ ] inside the cell. NO change in cell. H2O moves in and out at the same rate.

21. Another look:

22. Plant Cell Hypotonic Solution high H2O [ ] outside the cell , H2O flows in , pressure builds up , cytoplasm pushes against cell membrane & wall. This pressure is Turgor Pressure. The cell looks stiff or Turgid.

23. Plant Cell Hypertonic Solution low H2O [ ] outside cell , H2O flows out , pressure drops, plasma membrane may collapse which is called plasmolysis. The cell is referred to as being wilted or flaccid.

24. Plant Cell Isotonic Solution The H2O [ ] outside the cell equals the H2O [ ] inside the cell. NO change in the cell. H2O moves inside & outside at the same rate.

25. Another look:

26. Facilitated Diffusion • Form of PT (no ATP) • Uses Passive Channel Proteins in cell membrane to transport large molecules or ions across cell membrane. • These channel proteins act as ports , shielding these molecules from the cell membrane. • Still moving from an area of high [ ] to an area of low [ ].

27. Glucose molecules Protein channel

28. Active Transport (AT) • AT requires ATP to move materials across the cell membrane against the [ ] gradient. • 3 Types of AT : 1. Endocytosis 2. Exocytosis 3. Active Channel Proteins

29. Endocytosis • A cell extends its plasma membrane around very large items and engulfs them , moving from an area of decreased [ ] to an area of increased [ ]. • 2 Types : 1. Pinocytosis (small particles & liquid) 2. Phagocytosis (large particles)

30. Pinocytosis

31. Exocytosis • Excreting materials from a cell packaged in vesicles. • The cell uses ATP energy. • Exocytosis • Exocytosis 2

32. Active Channel Proteins • Proteins or “pumps” in the cell membrane bind to small molecules or ions and by changing shape move molecules from an area of low [ ] to high [ ] . • Movement against the Concentration Gradient • Particles are drawn against the concentration gradient using active channels that open and close using cellular energy ATP • Animation

33. Homeostasis • All these examples of cellular traffic are designed to help the cell maintain a state of balance between the inside and the outside of the cell.