Cell Membrane Function (Movement Across the Cell Membrane)

1. Bi 1a Cell Membrane Structure and Function Cell Membrane Function(Movement Across the Cell Membrane)

2. Cell (plasma) membrane • Cells need an inside & an outside… • separate cell from its environment • cell membrane is the boundary IN food - sugars - proteins - fats salts O2 H2O OUT waste - ammonia - salts - CO2 - H2O products - proteins cell needs materials in & products or waste out

3. Building a membrane • How do you build a barrier that keeps the watery contents of the cell separate from the watery environment? FATS LIPIDS Remember: oil & water don’t mix!! What substance do you know that doesn’t mix with water?

4. inside cell outside cell Lipids of cell membrane • Membrane is made of special kind of lipid • phospholipids • “split personality” • Membrane is a double layer • phospholipid bilayer “attracted to water” phosphate lipid “repelled by water”

5. Semi-permeable membrane • Cell membrane controls what gets in or out • Need to allow some materials — but not all — to pass through the membrane • semi-permeable • only some material can get in or out So what needs to get across the membrane? lipids aa O2 H2O salt sugar waste

6. inside cell outside cell Crossing the cell membrane • What molecules can get through the cell membrane directly? • fats and oils can pass directly through lipid salt waste but… what about other stuff? sugar aa H2O

7. Cell membrane channels • Need to make “doors” through membrane • protein channels allow substances in & out • specific channels allow specific material in & out • H2O channel, salt channel, sugar channel, etc. inside cell H2O aa sugar salt outside cell waste

8. How do you build a semi-permeable cell membrane? • Channels are made of proteins • proteins both “like” water & “like” lipids bi-lipid membrane protein channelsin bi-lipid membrane

9. Protein channels • Proteins act as doors in the membrane • channels to move specific molecules through cell membrane HIGH LOW

10. Movement through the channel • Why do molecules move through membrane if you give them a channel? HIGH ? LOW ?

11. Molecules move from high to low • Diffusion • move from HIGH to LOW concentration

12. Diffusion • Move from HIGH to LOW concentration • passive transport • no energy needed diffusion

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

14. Simple Diffusion • Move from HIGH to LOW fat fat fat Which way will fat move? inside cell fat fat fat LOW HIGH fat outside cell fat fat fat fat fat fat fat

15. Facilitated Diffusion • Move from HIGH to LOWthrough a channel sugar sugar sugar sugar inside cell sugar sugar LOW Which way will sugar move? HIGH outside cell sugar sugar sugar sugar sugar sugar sugar

16. Diffusion • Move from HIGH to LOW concentration • directly through membrane • simple diffusion • no energy needed • help through a protein channel • facilitated diffusion (with help) • no energy needed HIGH LOW

17. inside cell inside cell outside cell outside cell Simple vs. facilitated diffusion simple diffusion facilitated diffusion lipid H2O protein channel H2O

18. 1 4 2 3 Diffusion • Random motion drives diffusion • Movement is based on kinetic energy (speed), charge, and mass of molecules • Equilibrium is reached when there is an even distribution of solute molecules (water)

19. Active transport • Cells may need molecules to move against concentration “hill” • need to pump “uphill” • from LOW to HIGHusing energy • protein pump • requires energy • ATP ATP

20. LOW HIGH 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 ATP “The Doorman”

21. Active transport • Many models & mechanisms ATP ATP antiport symport

22. Transport summary simplediffusion facilitateddiffusion ATP activetransport

23. How about large molecules? • Moving large molecules into & out of cell • through vesicles & vacuoles • REQUIRES ENERGY • endocytosis • phagocytosis = “cellular eating” • pinocytosis = “cellular drinking” • exocytosis exocytosis

24. Endocytosis fuse with lysosome for digestion phagocytosis non-specificprocess pinocytosis triggered bymolecular signal receptor-mediated endocytosis

25. OsmosisMovement of Water Across Cell Membrane

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

27. 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

28. Osmosis • Diffusion of water through a semi-permeable membrane • Semi-permeable: permeable to solvents (WATER), but not to large molecules • High [water] to low [water] • Dissolved molecules (i.e. glucose, starch) are called solutes • REMEMBER: Water = solvent Glucose, Starch = solutes

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

30. 1 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 • ATP • plant cells • turgid = full • cell wall protects from bursting KABOOM! ATP No problem,here freshwater

31. 2 Keeping right amount of water in cell I’m shrinking,I’m shrinking! saltwater • Saltwater ( lots of salt) • HYPERTONIC • a cell in salt water • low concentration of water around cell • cell loses water • example: shellfish • problem: cell loses water • in plants: plasmolysis • in animals: shrinking cell • solution: take up water I willsurvive!

32. 3 Keeping right amount of water in cell That’sbetter! balanced • Balanced conditions (ISOTONIC ) • no difference in concentration of water between cell & environment • cell in equilibrium • example:blood • problem: none • water flows across membrane equally, in both directions • volume of cell doesn’t change I couldbe better…

33. Effect of Water on Cells • Hypertonic Environment • High [solute], low [water] • Hypotonic Environment • High [water], low [solute] • Isotonic Environment • [water] = [solute] Hypertonic Hypotonic Isotonic Part 3 pg. 85

34. Isotonic Predictions? Hypertonic Hypotonic Osmosis in Red Blood Cells • Sheep red blood cells • 0.9% saline • 10% NaCl • Distilled water Crenation

35. Effect of Water on red blood cell

38. Hypertonic Predictions? Hypotonic Osmosis in Plant Cells Plasmolysis • Elodealeaves • 10% NaCl • Distilled water

39. THOUGHT QUESTIONS WHY ARE PASSIVE TRANSPORT ( diffusion, facilitated diffusion, osmosis) and ACTIVE TRANSPORT IMPORTANT TO THE CELL? HOW DOES THE CELL MAINTAIN ITS HOMEOSTASIS?