1. Membrane Structure and Function Ch 7

2. Cell Membrane http://www.ncnr.nist.gov/programs/reflect/rp/biology/cell_membrane_p2.jpg Aka: Plasma membrane, phosopholipid bilayer basic structure Selectively permeable: allows some substances to cross more easily than others. 07_11MembraneSelectivity_A.swf 07_11MembraneSelectivity_A.swf http://image.tutorvista.com/content/feed/u303/lipidbilayer.gif

3. Components and Structure of the cell membrane Fluid Mosaic Model – The membrane moves around – Various substances are embedded in the phospholipid bilayer Lipids: amphipathic (has a hydrophillic and hydrophobic region) Proteins: move laterally and help with transport of substances Carbohydrates: extend from surface, docking port

4. Fluidity of Membranes Held together by weak hydrophobic interactions Most lipids & some proteins move laterally (sideways) rarely cross the hydrophobic core Fluidity is temp dependent: cooler = less fluid As temperatures decrease eventually the membrane will become rigid – Unsaturated phospholipids stay fluid longer – kinked due to double bonds – Saturated phosphlipids are more closely packed Cholesterol in Animal cells limits fluidity – Temperature buffer

5. Fig. 7-5b (b) Membrane fluidity Fluid Unsaturated hydrocarbon tails with kinks Viscous Saturated hydro- carbon tails Fluidity of Membranes

6. Membrane Proteins Integral – Span all or part of membrane Hydrophobic: nonpolar a.a. w/ α helices Hydrophillic: extend to inner & outer surfaces Peripheral– surface proteins – Held in place by cytoskeleton (inside cell) and extra cellular matrix (ECM) (outside cell)

7. Carbohydrates and Cell membranes Cell to cell recognition, surface tags that allow cells to recognize each other (good or bad) Glycolipids: carb attached to lipid Glycoprotein: carb attached to protein

8. Synthesis of Membranes 1.Proteins & lipids made in ER, Carbs are added & modified 2.Golgi: further Carb modification & Carbs are added to lipids = glycolipids 3.The various proteins leave Golgi via vesicles to plasma membrane 4.Vesicles fuse with plasma membrane, this releases secretory proteins and positions carbs of membrane proteins on outside of membrane

9. Fig. 7-10 ER 1 Transmembrane glycoproteins Secretory protein Glycolipid 2 Golgi apparatus Vesicle 3 4 Secreted protein Transmembrane glycoprotein Plasma membrane: Cytoplasmic face Extracellular face Membrane glycolipid

10. Selective Permeability Passive transport – no energy required – “down” a concentration gradient Simple Diffusion 07_11Diffusion_A.swf 07_11Diffusion_A.swf Facilitated Diffusion – Channel or Carrier Osmosis Active Transport – energy required – against a concentration gradient Ion Pumps Cotransport Bulk Transport – Exocytosis – Endocytosis

11. Simple vs. Facilitated Diffusion Simple: Substances move with the concentration gradient NO ENERGY REQUIRED – Non polar (CO 2 & Hydrocarbons) can diffuse through the lipid portion of the membrane) – Polar molecules pass through slowly (glucose & water) Facilitated Diffusion NO ENERGY REQUIRED Transport Proteins – Channel proteins, hydrophilic to allow ions to pass through Ion channels are gated channels – Aquaporins: let water through membrane – Carrier Proteins: change shape & hold on to substance as it passes through the membrane

12. Osmosis: The diffusion of water 07_13Osmosis_A.swf Diffusion of “free” water Tonicity – the ability of a cell to gain or lose water – Isotonic – balanced – no net movement of H 2 O Plants - flacid – Hypertonic – H 2 O moves out Solute concentration greater outside cell Plants – plasmolysis (shrivel up) – Hypotonic – H 2 O moves in Solute concentration greater inside cell Plants – turgid (swell) Osmoregulation – the regulation of H 2 O (contractile vacuole in some fresh water organisms)

13. Active Transport: REQUIRES ENERGY & Against the conc. gradient 07_16ActiveTransport_A.swf Ion Pumps: – Sodium-Potassium (Na +, K + ) pump, 3 Na + out for every 2 K + in to cell, creates a voltage potential – Proton pump in plants, fungi & bacteria moves H + out of cytoplasm into extracellular solution and creates a voltage potential Electrochemical gradient is how ions move in and out of cells

14. Active Transport: Cotransport: – A substance is actively pumped across the cell membrane using ATP. – The same substance naturally diffuses back across the cell membrane w/ it’s conc. gradient – When it diffuses back, it brings another substance with it, against that substances conc. gradient using the electrochemical gradient that was set up by the first substance. – Ex: Sucrose-H + cotransport & diarrhea medications

15. Fig. 7-19 Proton pump – – – – – – + + + + + + ATP H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Diffusion of H + Sucrose-H + cotransporter Sucrose

16. Bulk Transport: Requires energy Exocytosis Transport vesicle from golgi fuses w/ plasma membrane and then the material is exited form the cell 07_20Exocytosis_A.swf Endocytosis: Cell takes in bio material by creating a vesicle from plasma membrane – Phagocytosis: cellular eating – Pinocytosis: cellular drinking – Receptor-mediated endocytosis: binding of ligand to receptor triggers vesicle formation – 07_20cReceptMedEndocyt_A.swf 07_20cReceptMedEndocyt_A.swf

17. Concept Check Transport 1. Draw three cells in the following environments and describe the water movement between the cell & environment: – Cell in hypotonic environment – Cell in hypertonic environment – Cell in isotonic environment 2. Describe how the structure of membrane proteins is important to the selectively permeable membrane in cells. Include the following terms: hydrophobic, hydrophillic, amino acids, tertiary protein structure.