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Cell Membranes

Cell Membranes. The Cell Membrane. Cell Membrane : . At Very High Magnification & in color. Membrane Structure. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellMembranes.html. Cell Membrane.

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Cell Membranes

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  1. Cell Membranes

  2. The Cell Membrane

  3. Cell Membrane: At Very High Magnification & in color

  4. Membrane Structure http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellMembranes.html

  5. Cell Membrane Every cell is encircled by a membrane and most cells contain an extensive intracellular membrane system. Membranes fence off the cell's interior from its surroundings. Membranes let in water, certain ions and substrates and they excrete waste substances. They act to protect the cell. Without a membrane the cell contents would diffuse into the surroundings, information containing molecules would be lost and many metabolic pathways would cease to work: The cell would die! www.biologie.uni-hamburg.de/b-online/e22/22.htm

  6. Cell Membranes: • Surround all cells • Fluid-like composition…like soap bubbles • Composed of: • Lipids in a bilayer • Proteins embedded in lipid layer (called transmembrane proteins) • And, Proteins floating within the lipid sea (called integral proteins) • And Proteins associated outside the lipid bilayer (peripheral).

  7. Membrane Lipids • Composed largely of phospholipids • Phospholipids composed of….glycerol and two fatty acids + PO4 group • P-Lipids are polar molecules… P-Lipids are represented like this

  8. Phospholipid Molecule Model phosphate (hydrophilic) polar glycerol fatty acids (hydrophobic) nonpolar

  9. Membrane Lipidsform a Bilayer Outside layer Inside Layer

  10. Fluid Mosaic Membrane

  11. Membrane Proteins • Integral: embedded within bilayer • Peripheral: reside outside hydrophobic region of lipids

  12. Membrane Proteins Text pg 80

  13. Integral membrane proteins

  14. Peripheral membrane proteins

  15. Membrane Models Fluid Mosaic Model - lipids arranged in bilayer with proteins embedded or associated with the lipids.

  16. Fluid Mosaic Membrane

  17. Evidence for the Fluid Mosaic Model (Cell Fusion) Frey and Edidin http://bio.winona.edu/berg/ANIMTNS/Frey.htm

  18. Lateral Diffusion of Proteins

  19. Membrane Functions allows for different conditions between inside and outside of cell subdivides cell into compartments with different internal conditions allows release of substances from cell via vesicle fusion with outer membrane: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/exocyt.gif

  20. Membrane Permeability • Biological membranes are physical barriers..but which allow small uncharged molecules to pass… • And, lipid soluble molecules pass through • Big molecules and charged ones do NOT pass through • Semi-permeable / selectively permeable

  21. How to get other molecules across membranes?? • There are two ways that the molecules typically move through the membrane: • passive transport and active transport • Active transport requires that the cell use energy that it has obtained from food to move the molecules (or larger particles) through the cell membrane. • Passive transport does not require such an energy expenditure, and occurs spontaneously.

  22. Membrane Transport MechanismsI. Passive Transport • Diffusion- simple movement from regions of high concentration to low concentration • Osmosis- diffusion of water across a semi-permeable membrane • Facilitated diffusion- protein transporters which assist in diffusion

  23. Membrane Transport MechanismsII. Active Transport • Active transport- proteins which transport against concentration gradient. • Requires energy input • Endo cytosis • Exo cytosis

  24. Diffusion Movement generated by random motion of particles. Caused by internal thermal energy. Movement always from region of high free energy(high concentration) to regions of low free energy (low conc.) How Diffusion Works

  25. Osmosis Movement of water across a semi-permeable barrier. Example: Salt in water, cell membrane is barrier. Salt will NOT move across membrane, water will. How Osmosis Works

  26. cell Osmosis in Hypertonic medium • Hypertonic solutions- shrink cells

  27. Osmosis in Hypotonic medium • Hypotonic solutions- swell cells • “Hypos make hippos”

  28. For more animations view: http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

  29. For Osmosis in Action View frozen frogs at: http://www.pbs.org/wgbh/nova/sciencenow/3209/05.html How did the frog use the principles of osmosis and diffusion to survive the winter? Make sure you use the following terms appropriately in your description: hypertonic, hypotonic, solute, solvent, diffusion, osmosis, cytolysis, crenation, isotonic and semi-permeable membrane.

  30. Endocytosis • Transports macromolecules and large particles into the cell. • Part of the membrane engulfs the particle and folds inward to “bud off.” • Phagocytosis • Pinocytosis

  31. Endocytosis • Receptor Mediated Endocytosis

  32. Putting Out the Garbage • Vesicles (lysosomes, other secretory vesicles) can fuse with the membrane and open up the the outside…

  33. Exocytosis (Cellular Secretion) http://bio.winona.edu/berg/ANIMTNS/Secrtion.htm

  34. Membrane Permeability 1) lipid soluble solutes go through faster • smaller molecules go faster 1) uncharged & weakly charged go faster 2) Channels or pores may also exist in membrane to allow transport 1 2

  35. Types of Protein Transporters: Ion Channels • work by facilitated diffusion No E! • deal with small molecules... ions • open pores are “gated”- Can change shape. • How? • How much gets in? • important in cell communication Receptors Linked to a Channel Protein

  36. Ion Channels • Work fast: No conform. changes needed • Not simple pores in membrane: • specific to different ions (Na, K, Ca...) • gates control opening • Toxins, drugs may affect channels • saxitoxin, tetrodotoxin • cystic fibrosis

  37. Ion Channels • Channel proteins or carrier proteins allow the facilitated diffusion of solutes down their concentration gradients or electrochemical gradients. • Carrier proteins allow the active transport of solutes up their concentration gradients or electrochemical gradients.

  38. Cystic Fibrosis • Fatal genetic disorder • Mucus build-up results in lung and liver failure • Patients die between 4 and 30 yrs. • Single gene defect • 1 in 25 Caucasians carry 1 bad gene copy • 1 in 2500 kids has it in Canada • Testing

  39. CF Cont… • Proteins for diffusion of salt into the airways don't work.  • Less salt in the airways means less water in the airways.  • Less water in the airways means mucus layer is very sticky (viscous). • Sticky mucus cannot be easily moved to clear particles from the lungs.     • Sticky mucus traps bacteria and causes more lung infections. http://www.the-aps.org/education/lot/cell/HotT.htm

  40. Transport ProteinsFacilitated Diffusion & Active Transport • move solutes faster across membrane • highly specific to specific solutes • can be inhibited by drugs

  41. Types of Protein Transporters A. Facilitated Diffusion Assist in diffusion process. Solutes go from High conc to Low conc. Examples: Glucose transporters http://bio.winona.msus.edu/berg/ANIMTNS/FacDiff.htm

  42. Facilitated DiffusionThe Glucose Transporters • Transport of glucose into cells mediated by proteins in the GLUT (GLUcose Transport) family of transporters. There are 7 different, but related, proteins. But, only four (GLUT1-4) are known to be involved in glucose transport. • All GLUT proteins share a set of similar structural features and are all about 500 amino acids in length (giving them a predicted molecular weight of about 55,000 Daltons) • Glucose uptake shows saturation and glucose uptake can be inhibited by drugs A classic Membrane Transport protein How Facilitated Diffusion Works

  43. Glucose TransporterCharacteristics: • integral protein: spans the membrane • 12 alpha helices woven into membrane • 55,000 mol. wt.

  44. Glucose Transporter:How it works.. • glucose binds to outside of transporter (exterior side with higher glucose conc.) • glucose binding causes a conform. change in protein • glucose drops off inside cell • protein reassumes 1st configuration

  45. Types of Protein Transporters: Active Transport • carrier proteins • go against the concentration gradients Low to High • require Energy to function (ATP, PEP, light energy, electron transport)

  46. Membrane Transport:Active transport Movement from region of low free energy(low concentration) to regions of high free energy (high conc.) Requires energy input Cotransport Sodium-Potassium Exchange Pump Endocytosis and Exocytosis Proton Pump

  47. Active Transport:Sodium-Potassium Pump Na+ low Na+ high K+ low K+ high Balance of the two ions goes hand-in-hand ATP required for maintenance of the pump

  48. The sodium/potassium pump • All nerve and muscle cells have a high internal potassium ion concentration and a low internal sodium ion concentration. [Ki=166 mM; Ko=5 mM; Nai=18 mM; Nao=135 mM]. • Early on, it was thought that the nerve and muscle membranes were relatively impermeable to these ions and that the difference in ionic concentration was set up in early development of the cells. The membrane then became impermeable. • The later availability and use of radioactive Na and K ions showed that this was not true and that there was a metabolic pump that pumped Na out of the cell and K in; the ratio being 3 Na pumped out of the cell for every 2 K pumped into the cell. How it Works

  49. Is a Protein Involved ? • Experiments showed a dependency of both Na and K ions for pump to work • Pump was inhibited by ouabain (a drug) • 1957: an ATPase enzyme was found to be associated with Na/K pumping • Studies showed this ATPase capable of pumping Na/K ions • Text pg 90

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