Cell Membrane and the Movement across it!

1. Cell Membrane and the Movement across it!

2. Cell (plasma) membrane • Cells need an inside & an outside… • separate cell from its environment • cell membrane is the boundary Can it be an impenetrable boundary? NO! OUT waste ammonia salts CO2 H2O products IN food carbohydrates sugars, proteins amino acids lipids salts, O2,H2O OUT IN cell needs materials in & products or waste out

3. A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer Cell Membrane video

4. inside cell outside cell Lipids of cell membrane • Membrane is made of phospholipids • phospholipid bilayer phosphate hydrophilic lipid hydrophobic

5. Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

6. Membrane Proteins • Name and Location of membrane proteins:

7. Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Enzymeactivity Cell surfacereceptor Cell adhesion Cell surface identity marker Attachment to thecytoskeleton

8. The many functions of proteins…. • Channel proteins – wide open passage • Ion channels – electrically 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

9. Membrane carbohydrates • Play a key role in cell-cell recognition • distinguishing one cell from another • antigens • EX: important in organ & tissue development • EX: basis for rejection of foreign cells by immune system

10. Cholesterol • Provides stability in animal cells • “temperature buffer” quality for membrane • Replaced with sterols in plant cells

11. 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 more fluid • cold-adapted organisms, like winter wheat • increase % in autumn • cholesterol in membrane

12. Getting through cell membrane • Passive transport • No energy needed • Movement down concentration gradient • Active transport • Movement against concentration gradient • low  high • requires ATP

13. Diffusion • 2nd Law of Thermodynamics- Universe tends towards disorder Does molecular movement stop here? • Diffusion • movement from highlow concentration

14. low  high Simple diffusion across membrane Which way will lipid move? lipid lipid lipid inside cell lipid lipid lipid lipid outside cell lipid lipid lipid lipid lipid lipid lipid

15. Diffusion of 2 solutes • Each substance diffuses down its own concentration gradient, independent of concentration gradients of other substances Diffusion Demo Video

16. Facilitated diffusion • Move from HIGH to LOW concentration through a protein channel • passive transport • no energy needed • facilitated = with help

17. Gated channels • Proteins that open only in presence of stimulus (signal) • stimulus usually different from transported molecule • ex:ion-gated channels • ex:voltage-gated channels

18. 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

19. Transport summary

20. How about large molecules? • Moving large molecules into & out of cell requires ATP(energy)! • through vesicles & vacuoles • endocytosis • phagocytosis = “cellular eating” • pinocytosis = “cellular drinking” • receptor-mediated endocytosis • exocytosis exocytosis

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

22. Endocytosis…

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

24. Osmosis is diffusion of water • Diffusion of water from high concentration of water to low concentration of water • across a semi-permeable membrane Why does the water level rise on one side?

25. 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

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

27. Cell adaptations Protists Only! • animal cell • contractile vacuoles - pumps H2O out of cell = ATP • plant cell • Turgid (turgor pressure) • Cell wall • plasmolysis= wilt

28. Osmosis… .05 M .03 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

29. 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 waterpotential will decreaseaccordingly. • Which has the greater water potential: • .2M or .8M? • Which has the greater water potential: • 20% or 80% water?

30. aa O2 CH CHO CO2 aa NH3 CHO O2 CH O2 aa CO2 CO2 O2 NH3 aa NH3 CO2 NH3 CO2 CO2 NH3 NH3 O2 CO2 CO2 CO2 NH3 aa NH3 NH3 CHO CO2 CO2 aa CH Animal systems evolved to support multicellular life single cell intracellular waste but whatif the cells are clustered? extracellular waste for nutrients in & waste out Diffusion too slow!

31. CO2 CO2 O2 NH3 aa NH3 CO2 NH3 CO2 CO2 NH3 NH3 O2 CO2 CO2 CO2 NH3 aa NH3 NH3 CHO CO2 CO2 aa CH Overcoming limitations of diffusion • Evolution of exchange systems for • distributing nutrients • circulatory system • removing wastes • excretory system • gas exchange • respiratory system systems to support multicellular organisms

32. When is Diffusion Needed? • Respiratory and Circulatory systems • Oxygen/CO2 transport into and out of bloodstream • Skins, gills, alveoli, capillaries • Excretory systems • Movement of wastes into or out of blood • Skin, nephridia, nephrons, gills Q: What do these systems have in common for diffusion to occur? Large surface area

33. cilia Gas exchange in many forms… one-celled amphibians echinoderms insects fish mammals • • endotherm vs. ectotherm size water vs. land

34. Counter current exchange system • Water carrying gas flows in one direction, blood flows in opposite direction just keepswimming….

35. water blood How counter current exchange works back • Blood & water flow in opposite directions • maintains diffusion gradient over whole length of gill capillary • maximizing O2 transfer from water to blood front 70% 40% 100% 15% water 60% 30% counter-current 90% 5% blood 50% 70% 100% 50% 30% 5% concurrent

36. Gas Exchange on Land • Advantages of terrestrial life • air has many advantages over water • higher concentration of O2 • O2 & CO2 diffuse much faster through air • respiratory surfaces exposed to airdo not have to be ventilated as thoroughly as gills • air is much lighter than water & therefore much easier to pump • expend less energy moving air in & out • Disadvantages • keeping large respiratory surface moist causes high water loss • reduce water loss by keeping lungs internal

37. H O H | | | –C– C–OH N | H R Animalspoison themselvesfrom the insideby digestingproteins! Intracellular Waste • What waste products are made inside of cells? • what do we digest our food into… • carbohydrates = CHO • lipids = CHO • proteins = CHON • nucleic acids = CHOPN  CO2 +H2O  CO2 +H2O  CO2 +H2O + N  CO2 +H2O + P + N cellular digestion…cellular waste CO2 + H2O NH2= ammonia

38. Nitrogen waste • Aquatic organisms • can afford to lose water • ammonia • most toxic • Terrestrial • need to conserve water • urea • less toxic • Terrestrial egglayers • need to conserve water • need to protectembryo in egg • uric acid • least toxic

39. H H H H N N C O Land animals • Nitrogen waste disposal on land • need to conserve water • must process ammonia so less toxic • urea = larger molecule = less soluble = less toxic • 2NH2 + CO2 = urea • produced in liver • kidney • filter solutes out of blood • reabsorb H2O (+ any useful solutes) • excrete waste • urine = urea, salts, excess sugar & H2O • urine is very concentrated • concentrated NH3 would be too toxic Ureacosts energyto synthesize,but it’s worth it! mammals

40. Animal Osmoregulation (blood solute levels) • Kidneys – generate urine by filtering wastes from blood • Nephrons – basic unit of kidney • Water will move towards urine or blood as it becomes hypertonic via AQUAPORINS • Anti-Diuretic Hormone increases water movement back to blood….why? • Blood pressure is highly regulated by the kidney because without pressure, there is no filtration = toxic blood = death!!!

41. Osmotic control in nephron • How is all this re-absorption achieved? • tight osmotic control to reduce the energy costof excretion • use diffusioninstead of active transportwherever possible the value of acounter current exchange system

42. hypotonic Osmoregulation • Water balance vs. Habitat • freshwater • hypotonic to body fluids • water flow into cells & salt loss • saltwater • hypertonic to body fluids • water loss from cells • land • dry environment • need to conserve water • may also need to conserve salt hypertonic Why do all land animals have to conserve water? • always lose water (breathing & waste) • may lose life while searching for water