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Cell Membranes

Cell Membranes. The Cell Membrane. Cell Membrane : . At Very High Magnification & in color. Phospholipid Molecule Model. phosphate (hydrophilic/polar). glycerol fatty acids (hydrophobic/nonpolar). Membrane Structure. Hydro Philic/philia Phobic/phobia Polar=soluble in water.

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

  5. Membrane Structure HydroPhilic/philiaPhobic/phobiaPolar=soluble in water

  6. 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!

  7. 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 (called peripheral proteins).

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

  9. Membrane Lipidsform a Bilayer Outside layer Inside Layer

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

  11. Membrane Models Fluid Mosaic Model - lipids arranged in bilayer with proteins embedded or associated with the lipids. What color are the lipids? What color are the integral proteins? What color are the peripheral proteins?

  12. Fluid Mosaic Model of the Cell Membrane

  13. Evidence for the Fluid Mosaic Model (Cell Fusion) Frey and Edidin

  14. 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:

  15. 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

  16. Solution = solute + solventSolute-- the thing being dissolvedSolvent--does the dissolvingkool-aid chocolate milkTerms that refer to solute:HyperHypoIso

  17. How to get other molecules across membranes?? • There are two ways to move through the membrane: • passive transport and active transport • Active transport requires energy (that the cell has obtained from food to move the molecules through the cell membrane) • Passive transport does not require energy

  18. 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

  19. Membrane Transport MechanismsII. Active Transport • Active transport- proteins which transport against concentration gradient. • Requires energy input (uses ATP) - Endocytosis • Exocytosis • Receptor mediated endocytosis

  20. 1.What is the solute? 2. What diffuses? 3.Why? 4.Is this diffusion or osmosis? 5.Which side is hypertonic? 6.Which side is hypotonic? 7.Why doesn’t the sugar diffuse?

  21. 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.

  22. cell Osmosis in Hypertonic medium Hypertonic solutions- shrink cells Plasmolysis in Plant Cells Crenation in Animal Cells What happens when you eat salty chips?

  23. Osmosis in Hypotonic medium Hypotonic solutions- swell cells “Hypos make hippos” Cytolysis in Animal Cells Turgor Pressure in Plant Cells http://www.kscience.co.uk/animations/turgor.htm

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

  25. 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.

  26. Osmosis & Food Preservation • Food can be preserved by causing any microorganism that comes in contact with it to become plasmolysed and, therefore, shrivel and die. To do this food is placed in a high salt or sugar medium. The salt or sugar concentration is higher than the cytoplasm of bacteria or fungi. Bacteria or fungi, that contaminate the food, will lose water by osmosis and their metabolism will decline. Many will die but some bacteria may survive by forming dormant resistant endospores. Meat and fish are often preserved in salt. Fruit is commonly preserved in sugar as in jam or syrup.

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

  28. Phagocytosis • Pseudopods • Phagocytes • Macrophages (phage)_

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

  30. Exocytosis (Cellular Secretion)

  31. Types of Protein Transporters A. Facilitated Diffusion Assist in diffusion process. Solutes go from High conc to Low conc. Examples: Glucose transporters Carrier Proteins Protein Channels

  32. 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)

  33. Membrane Transport:Active transport Movement from region of low free energy(low concentration) to regions of high free energy (high conc.) Requires energy input

  34. Sodium-Potassium Pump

  35. Resources • http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellMembranes.html • www.biologie.uni-hamburg.de/b-online/e22/22.htm • More Animations: http://www.kscience.co.uk/animations/anim_1.htm • http://fig.cox.miami.edu/~cmallery/150/memb/membranes.htm • Pictures: http://biologycorner.com/resources/ • 1st Semester Final Review

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