2. AP Biology The Cell Membrane The Fluid Mosaic Model

3. AP Biology Cell membrane must be more than lipids…  1972 - S.J. Singer & G. Nicolson proposed that membrane proteins are inserted into the phospholipid bilayer It’s like a fluid… It’s like a mosaic… It’s the Fluid Mosaic Model!

4. AP Biology 1. Phospholipids Fatty acid Phosphate  Phosphate head + Choline  hydrophilic  Fatty acid tails  hydrophobic  Arranged as a bilayer Aaaah, one of those structure–function examples “repelled by water” “attracted to water”

5. AP Biology Membrane fat composition varies  Fat composition affects flexibility  membrane must be fluid & flexible  about as fluid as thick salad oil  % unsaturated fatty acids in phospholipids  keep membrane less viscous  cold-adapted organisms, like winter wheat  increase % in autumn  1b. cholesterol in membrane  Maintains the fluidity of the cell  especially in cold conditions

6. AP Biology Arranged as a Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads  Serves as a cellular barrier / border H2OH2O sugar lipids salt waste impermeable to polar molecules

7. AP Biology 2. Proteins  Determines what goes in and out  specific channels allow specific material across cell membrane  W/O water would never diffuse through inside cell outside cell sugaraa H2OH2O salt NH 3

8. AP Biology  Within membrane  nonpolar amino acids  hydrophobic  anchors protein into membrane  On outer surfaces of membrane in fluid  polar amino acids  hydrophilic  extend into extracellular fluid & into cytosol Proteins domains anchor molecule (EXTRA) Polar areas of protein Nonpolar areas of protein

9. AP Biology NH 2 H+H+ COOH Cytoplasm Retinal chromophore Nonpolar (hydrophobic)  -helices in the cell membrane H+H+ Porin monomer  -pleated sheets Bacterial outer membrane proton pump channel in photosynthetic bacteria aquaporin = water channel in bacteria function through conformational change = protein changes shape Examples H2OH2O H2OH2O H+H+ H+H+

10. AP Biology Membrane Proteins A. integral proteins  penetrate lipid bilayer, usually across whole membrane  transmembrane protein  ex: transport proteins 1. Channel – have a tube that allows materials to go from one side of the membrane to the other Channel  Aquaporin – no energy required 2. Carrier channel is specific, changes its shape for the substance, no E required Carrier channel  Glucose transport protein

11. AP Biology Membrane Proteins B. peripheral proteins  Embedded either on the ECM (outside) or cytoplasmic (inside) side  ECM side – links to ECM  Cytoplasmic – links to microfilaments or tethers organelles

12. AP Biology Fig. 6-30a Collagen Fibronectin Plasma membrane Proteoglycan complex Integrins CYTOPLASM Micro- filaments EXTRACELLULAR FLUID

13. AP Biology Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Signal Transduction Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion “Antigen” “Channel”

14. AP Biology Functions of Proteins in Cell Membrane 1. Transfer 1. Sodium-potassium pump (low  high con) Requires Energy, ATP is constant 2. Enzymatic Activity 1. Perform as enzymes 2. Carbohydrate metabolism 3. Signal Transduction 1. Receiving signals  effect 2. Stimulus  response!

15. AP Biology 4. Intercellular Joining 4. Plasmodesmata 5. Gap/tight junctions 5. Cell-cell recognition 6. Attachment 4. To ECM or filament

16. AP Biology 3. Oligarsaccharides (carb chains)  Glycolipids  A,B,O, Rh+, Rh-  Play a key role in cell-cell recognition  Glycoporteins  Ligans (anything that fits into carbon chains)  The carb chains vary from person to person

17. AP Biology Traffic Across the Membrane  Cross easily (no assitance)  Lipid soluble molecules (ex: sex hormones)  Gases (oxygen or CO 2 )  Cross w/ assistance  Water (and water soluble materials  Large molecules  Ions (sodium, potassium)  Proteins, glucose

18. AP Biology Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular fluid Cholesterol Cytoplasm Glycolipid Transmembrane proteins Filaments of cytoskeleton Peripheral protein Glycoprotein Phospholipids 1972, S.J. Singer & G. Nicolson proposed Fluid Mosaic Model

19. AP Biology Any Questions??

20. AP Biology 2007- 2008 PASSIVE TRANSPORT

21. AP Biology Diffusion  The tendency of a substance to spread out evenly inro space to reach dynamic equilibrium  Diffusion  movement from HIGH  LOW concentration  Diffusion  movement from HIGH  LOW concentration

22. AP Biology  Down concentration gradient  DOES NOT REQUIRE ENERGY  Due to the kinetic energy in the molecules

23. AP Biology Passive Transport  Diffusion across a membrane diffusionosmosis movement of water

24. AP Biology Facilitated Diffusion  Diffusion through protein channels  channels move specific molecules across cell membrane  no energy needed “The Bouncer” open channel = fast transport facilitated = with help HIGH LOW

25. AP Biology 2007- 2008 The Special Case of Water Movement of water across the cell membrane

26. AP Biology OsmosisOsmosis is just diffusion of water  Diffusion of water from HIGH concentration of water to LOW concentration of water  across a semi-permeable membrane  Tonicity - comparing the solute concentrations on opposite sides of a membrane, and the direction water moves

27. AP Biology 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

28. AP Biology  Hyperosmotic – area w/more water (hypotonic solution)  Hypoosmatic – area w/ less water

29. AP Biology freshwaterbalancedsaltwater Managing water balance  Cell survival depends on balancing water uptake & lossuptake & loss

30. AP Biology Aquaporins  Water moves rapidly into & out of cells  evidence that there were water channels  protein channels allowing flow of water across cell membrane 1991 | 2003 Peter Agre John Hopkins Roderick MacKinnon Rockefeller

31. AP Biology 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 Do you understand Osmosis…

32. AP Biology SEE WATER POTENTIAL POWERPOINT

33. AP Biology Active Transport conformational change  Cells may need to move molecules against concentration gradient – requires ATP Hydrolysis Cells may need  conformational shape change transports solute from one side of membrane to other (caused by ATP)  Low  High concentration  Use carrier proteins ATP Low High

34. AP Biology symportantiport Active transport  Many models & mechanisms ATP

35. AP Biology 1. Ion pumps 1. Sodium – Potassium pump (Na + /K - ) Sodium – Potassium (Na + /K - ) 2. Endocytosis

36. AP Biology Endocytosis phagocytosis pinocytosis receptor-mediated endocytosis fuse with lysosome for digestion non-specific process triggered by molecular signal

37. AP Biology  Moving large molecules into & out of cell  through vesicles & vacuoles  endocytosis  phagocytosis = “cellular eating” Engulfing phagocytosis  Intake of solid particles  Nonspecific Nonspecific  Creates a phagosome to be digested w/ a lysosome Creates  pinocytosis = “cellular drinking”  Intake of large fluid  nonspecific  Receptor mediated endocytosis  Intake of specific molecules (due to receptors)  Creation of clathrin-enclosed coated pit (vesicle) with specific molecules insideclathrin-enclosedspecific molecules

38. AP Biology 3. Exocytosis the release of substances from the cell

39. AP Biology Transport summary simple diffusion facilitated diffusion active transport ATP

40. AP Biology Any Questions??

41. AP Biology 2007- 2008 Ghosts of Lectures Past (storage)

42. AP Biology Diffusion through phospholipid bilayer  What molecules can get through directly?  fats & other lipids inside cell outside cell lipid salt aa H2OH2O sugar NH 3  What molecules can NOT get through directly?  polar molecules H2OH2O  ions (charged)  salts, ammonia  large molecules  starches, proteins

43. AP Biology Membrane fat composition varies  Fat composition affects flexibility  membrane must be fluid & flexible  about as fluid as thick salad oil  % unsaturated fatty acids in phospholipids  keep membrane less viscous  cold-adapted organisms, like winter wheat  increase % in autumn  cholesterol in membrane

44. AP Biology Diffusion across cell membrane  Cell membrane is the boundary between inside & outside…  separates cell from its environment IN food carbohydrates sugars, proteins amino acids lipids salts, O 2, H 2 O OUT waste ammonia salts CO 2 H2OH2O products cell needs materials in & products or waste out IN OUT Can it be an impenetrable boundary? NO!