1. AP Biology 2005-2006 Cell Membrane and the Movement across it!

2. AP Biology 2005-2006 Cell Membrane…more than just a barrier!

3. AP Biology 2005-2006 Cell (plasma) membrane  Cells need an inside & an outside…  separate cell from its environment  cell membrane is the boundary IN food carbohydrates sugars, proteins amino acids lipids salts, O 2, H 2 O OUT waste ammonia salts CO 2 H 2 O products cell needs materials in & products or waste out IN OUT Can it be an impenetrable boundary? NO!

4. AP Biology Lipids of cell membrane  Membrane is made of phospholipids  phospholipid bilayer phosphate lipid hydrophilic hydrophobic inside cell outside cell

5. AP Biology Phospholipid bilayer  What molecules can get through directly? inside cell outside cell fats & other lipids can slip directly through the phospholipid cell membrane, but… what about other stuff? lipid salt aa H2OH2O sugar NH 3

6. AP Biology 2005-2006 Membrane Proteins  Proteins determine most of membrane’s specific functions  cell membrane & organelle membranes each have unique collections of proteins  Membrane proteins:  peripheral proteins = loosely bound to surface of membrane  integral proteins = penetrate into lipid bilayer, often completely spanning the membrane = transmembrane proteins

7. AP Biology Membrane Protein Types  Channel proteins – wide open passage  Ion channels – gated  Aquaporins – water only, kidney and plant root only  Carrier proteins – change shape  Transport proteins – require ATP  Recognition proteins - glycoproteins  Adhesion proteins – anchors  Receptor proteins - hormones

8. AP Biology 2005-2006 A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

9. AP Biology 2005-2006 Membrane Carbohydrates  Play a key role in cell-cell recognition  ability of a cell to distinguish neighboring cells from another  important in organ & tissue development  basis for rejection of foreign cells by immune system

10. AP Biology Cholesterol  Provides stability in animal cells  Replaced with sterols in plant cells

11. AP Biology Getting through cell membrane  Passive transport  No energy needed  Movement down concentration gradient  Active transport  Movement against concentration gradient  low  high  requires ATP

12. AP Biology Diffusion  2nd Law of Thermodynamics - Universe tends towards disorder  Diffusion  movement from high  low concentration

13. AP Biology 2005-2006 Simple diffusion across membrane inside cell outside cell Which way will lipid move? low high  lipid

14. AP Biology Diffusion of 2 solutes  Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances

15. AP Biology 2005-2006 Facilitated diffusion  Move from HIGH to LOW concentration through a protein channel  passive transport  no energy needed  facilitated = with help

16. AP Biology 2005-2006 Gated channels  Some channel proteins open only in presence of stimulus (signal)  stimulus usually different from transported molecule  ex: ion-gated channels when neurotransmitters bind to a specific gated channels on a neuron, these channels open = allows Na + ions to enter nerve cell  ex: voltage-gated channels change in electrical charge across nerve cell membrane opens Na + & K + channels

17. AP Biology Active transport  Cells may need molecules to move against concentration situation  need to pump against concentration  protein pump  requires energy  ATP Na+/K+ pump in nerve cell membranes

18. AP Biology 2005-2006 Transport summary

19. AP Biology 2005-2006 How about large molecules?  Moving large molecules into & out of cell requires ATP!  through vesicles & vacuoles  endocytosis  phagocytosis = “cellular eating”  pinocytosis = “cellular drinking”  receptor-mediated endocytosis  exocytosis exocytosis

20. AP Biology 2005-2006 Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by ligand signal

21. AP Biology 2005-2006 The Special Case of Water Movement of water across the cell membrane

22. AP Biology 2005-2006 Osmosis is diffusion of water  Diffusion of water from high concentration of water to low concentration of water  across a semi-permeable membrane

23. AP Biology 2005-2006 Concentration of water  Direction of osmosis is determined by comparing total solute concentrations  Hypertonic - more solute, less water  Hypotonic - less solute, more water  Isotonic - equal solute, equal water hypotonichypertonic water net movement of water

24. AP Biology 2005-2006 Managing water balance  Cell survival depends on balancing water uptake & loss freshwaterbalancedsaltwater

25. AP Biology Hypotonicity  animal cell in hypotonic solution will gain water, swell & possibly burst (cytolysis)  Paramecium vs. pond water  Paramecium is hypertonic  H 2 O continually enters cell  to solve problem, specialized organelle, contractile vacuole  pumps H 2 O out of cell = ATP  plant cell  Turgid (turgor pressure)  Cell wall

26. AP Biology 2005-2006 Hypertonicity  animal cell in hypertonic solution will loose water, shrivel & probably die  salt water organisms are hypotonic compared to their environment  they have to take up water & pump out salt  plant cells  plasmolysis = wilt

27. AP Biology 2005-2006 Cell (compared to beaker)  hypertonic or hypotonic Beaker (compared to cell)  hypertonic or hypotonic Which way does the water flow?  in or out of cell.05 M.03 M Osmosis…

28. AP Biology Water Potential  Water moves from a place of greater water potential to a place of lesser water potential (net).  As the concentration of a solute increases in a solution, the water potential will decrease accordingly.  Which has the greater water potential: .2M or.8M?  Which has the greater water potential:  20% or 80% water?