Go to the “Free Response Help” link on my website to check out the Unit 2 FRQs!!!

1. Go to the “Free Response Help” link on my website to check out the Unit 2 FRQs!!!

2. Pre-Lab Preparation!!! • Go to “Labs & Lab Notebook” link on my website. • Click on “LabBench” link. • Click on “Lab 1: Diffusion & Osmosis.” • Read through Concepts #1-5, Design Exercises #1-2, and Self-Quiz ?s #1-3 of the Pre-Lab. • Answer the general questions COMPLETELY that are listed on your Lab Notebook Guidelines sheet. • Remember to ignore the “Water Potential” section and calculations • Due on Friday!!!

3. The Cell Membrane

4. Arranged as a Phospholipid bilayer • Serves as a cellular barrier / border polar hydrophilic heads nonpolar hydrophobic tails impermeable to polar molecules polar hydrophilic heads

5. Cell membrane defines cell • Cell membrane separates living cell from aqueous environment • But…separation CANNOT be complete, or the cell would die! • Controls traffic in & out of the cell • allows some substances to cross more easily than others • hydrophobic (nonpolar) particles can cross more easily than vs. hydrophilic (polar) particles

6. Permeability to polar molecules? • Membrane becomes “semi-permeable” via protein channels • specific channels allow specific material across cell membrane inside cell H2O aa sugar salt outside cell NH3

7. Cell membrane is more than lipids… • Transmembrane proteins embedded in phospholipid bilayer • create semi-permeable channels lipid bilayer membrane protein channelsin lipid bilyer membrane

8. Classes of amino acids nonpolar & hydrophobic

9. Classes of amino acids polar & hydrophilic

10. Membrane Proteins Polar areas of protein • 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 Nonpolar areas of protein

11. Porin monomer H+ Retinal chromophore b-pleated sheets NH2 Bacterial outer membrane Nonpolar (hydrophobic) a-helices in the cell membrane COOH Cytoplasm H+ H+ Examples aquaporin = water channel H2O H+ proton pump channel H2O

12. Many Functions of Membrane Proteins “Channel” Outside Plasma membrane Inside Transporter Enzymeactivity Cell surfacereceptor “Antigen” Cell adhesion Cell surface identity marker Attachment to thecytoskeleton

13. Glycoprotein Glycolipid Transmembrane proteins Peripheral protein Filaments ofcytoskeleton Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular fluid Phospholipids Cholesterol Cytoplasm Fluid Mosaic Model

14. Parts of the “mosaic”… • Fat composition affects flexibility • membrane must be fluid & flexible • % unsaturated fatty acids in phospholipids • keep membrane more fluid • Cold weather plants = increased unsaturated fatty acids (“winter wheat”) • cholesterol in membrane • prevents membrane from “freezing”

15. Membrane carbohydrates • Play a key role in cell-cell recognition • ability of a cell to distinguish one cell from another • antigens • basis for rejection of foreign cells by immune system

16. Movement across the Cell Membrane

17. Diffusion • 2nd Law of Thermodynamicsgoverns biological systems • universe tends towards disorder (entropy) • Diffusion • movement from HIGHLOW concentration

18. Simple Diffusion • Move from HIGH to LOW concentration • “passive transport” • no energy needed movement of water diffusion osmosis

19. (a) Diffusion of one solute. The membrane has pores large enough for molecules of dye to pass through. Random movement of dye molecules will cause some to pass through the pores; this will happen more often on the side with more molecules. The dye diffuses from where it is more concentrated to where it is less concentrated (called diffusing down a concentration gradient). This leads to a dynamic equilibrium: The solute molecules continue to cross the membrane, but at equal rates in both directions. Molecules of dye Membrane (cross section) WATER Equilibrium Net diffusion Net diffusion Diffusion of two solutes. Solutions of two different dyes are separated by a membrane that is permeable to both. Each dye diffuses down its own concen- tration gradient. There will be a net diffusion of the purple dye toward the left, even though the total solute concentration was initially greater on the left side. (b) Net diffusion Equilibrium Net diffusion Osmosis Net diffusion Net diffusion Equilibrium

20. HIGH LOW Facilitated Diffusion • Diffusion through protein channels • channels move specific molecules across cell membrane • no energy needed facilitated = with help open channel = fast transport

21. Active Transport • Cells may need to move molecules against concentration gradient • conformational shape change transports solute from one side of membrane to other • protein “pump” • “costs” energy = ATP conformationalchange

22. Active transport ATP

23. Getting through cell membrane • Passive Transport • Simple diffusion • diffusion of nonpolar, hydrophobic molecules • lipids • HIGH  LOW concentration gradient • Facilitated transport • diffusion of polar, hydrophilic molecules • through a (hydrophilic) protein channel • HIGH  LOW concentration gradient • Active transport • diffusion against concentration gradient • LOW  HIGH • uses a transport protein • A.K.A. “protein pump” • requires ATP ATP

24. Transport summary simplediffusion facilitateddiffusion ATP activetransport

25. How about large molecules? • Moving large molecules into & out of cell • through vesicles & vacuoles • endocytosis • phagocytosis = “cellular eating” • pinocytosis = “cellular drinking” • Exocytosis • Example: • Pancreas cell secreting insulin into bloodstream exocytosis

26. Endocytosis fuse with lysosome for digestion phagocytosis non-specific(takes in all molecules in extra-cellular fluid) pinocytosis triggered bymolecular signal receptor-mediated endocytosis

27. The Special Case of WaterMovement of water across the cell membrane

28. Osmosis is just diffusion of water • Water is very important to life, so we talk about water separately • Diffusion of water from HIGH concentration of water to LOW concentration of water • across a semi-permeable membrane

29. hypotonic hypertonic 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 water net movement of water

30. Managing water balance • Cell survival depends on balancing water uptake & loss freshwater balanced saltwater

31. Managing water balance • Hypotonic • a cell in fresh water • high concentration of water around cell • problem: cell gains water, swells & can burst • example: Paramecium • ex: water continually enters Paramecium cell • solution: contractile vacuole • pumps water out of cell • “osmoregulation” • plant cells • turgid = full • cell wall protects from bursting freshwater

32. Pumping water out • Contractile vacuole in Paramecium ATP

33. Managing water balance • Hypertonic • a cell in salt water • low concentration of water around cell • problem: cell loses water & can die • example: salinity increases in lake • plant cells • plasmolysis= wilt • can recover if conditions change saltwater

34. Managing water balance • Isotonic • animal cell immersed in mild salt solution • no difference in concentration of water between cell & environment • problem: none • no net movement of water • flows across membrane equally, in both directions • cell in equilibrium • volume of cell is stable • example:blood cells in blood plasma • slightly salty IV solution in hospital balanced

35. Aquaporins • protein channels allowing rapid flow of water across cell membrane • explains efficient nature of osmosis

36. Do you understand Osmosis… .05 M .02 M 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