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Cell Membranes Chapt 4

Cell Membranes Chapt 4. www.cellsalive.com/. The Cell Membrane. Fluid Mosaic Membrane. Text pg 80. Cell Membrane : Fluid Mosaic Model. At Very High Magnification & in color. Membrane Structure Flash movie too. CLICK ON THE PICTURE TO SEE AN ANIMATION OF THE CELL MEMBRANE. Cell Membrane.

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Cell Membranes Chapt 4

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  1. Cell MembranesChapt 4 www.cellsalive.com/

  2. The Cell Membrane

  3. Fluid Mosaic Membrane Text pg 80

  4. Cell Membrane: Fluid Mosaic Model At Very High Magnification & in color

  5. Membrane StructureFlash movie too.. CLICK ON THE PICTURE TO SEE AN ANIMATION OF THE CELL MEMBRANE

  6. Cell Membrane • Every cell is encircled by a membrane • 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 pass into the surroundings • Allows the cell to maintain HOMEOSTASIS = a constant internal environment kind of like the cell’s happy place 

  7. Cell Membranes Fluid-like structure…like soap bubbles Structure • Lipids in a bilayer • Protein-coated pores extend through membrane (MOSAIC) • Pores are very small and give the membrane polar properties • H2O penetrates membrane easily • Large polar molecules do not • Proteins embedded in lipid layer • Some proteins floating within the lipid sea (called integral proteins) • Some proteins associated outside the lipid bilayer (peripheral)

  8. 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

  9. Membrane Lipidsform a Bilayer Outside layer Inside Layer

  10. Quiz • If Phospholipids are polar, which end seeks out water and which avoids water?

  11. Phospholipid Molecule Model phosphate (hydrophilic) glycerol fatty acids (hydrophobic)

  12. Fluid Mosaic Membrane Text pg 80

  13. Functional Parts of the Cell Membrane • Cell Recognition Proteins unique markers that identify cells • Channel Proteins allows molecules and ions to move across • Carrier Proteins combine with substrate to move across membrane • Receptor Proteins bind to specific molecules (ex. hormone receptors) • Enzymatic Proteins proteins that run specific metabolic reactions

  14. Cell membrane contains carbohydrate (CHO’s) attached to proteins or lipids ( makes Glycoproteins and Glycolipids) • Found on outside of cell functioning as markers to identify cells to the immune system

  15. Auto-Immune Disease • Inflamed body cells in the joints or colon respectively being recognized by white blood cells as “non-self”. • Result is an immune response that causes injury to the body’s cells – in this case, the cartilege at the joints

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

  17. Membrane Proteins

  18. Integral membrane proteins

  19. Peripheral membrane proteins Integral

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

  21. Evidence for the Fluid Mosaic Model (Cell Fusion)

  22. More Evidence for the Fluid Mosaic Model

  23. 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

  24. How to get other molecules across membranes?? • There are three ways that the molecules typically move through the membrane: • Facilitated transport • Passive transport • 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. • Facilitated and Passive transport does not require such an energy expenditure, and occur spontaneously.

  25. 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

  26. Membrane Transport MechanismsII. Active Transport • Active transport- proteins which transport against concentration gradient. • Requires energy input

  27. Diffusion • Movement generated by random motion of particles. • Applies to any molecule/requires NO ENERGY!! • Movement always from region of high concentration to low concentration

  28. Diffusion continued • Lipid soluble molecules (alcohols) and gases (O2 and CO2) pass easily thru the membrane • H2O passes through protein channels • Large molecules and charged ions have difficulty passing thru (charge on membrane = polarity)

  29. 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. Click Picture Above for an Osmosis Demo

  30. Tonicity of Solutions Tonicity = the strength of a solution that a cell is placed in 3 Tonicity scenarios you must know!! • Isotonic • equal conc. of particles inside / out of the cell • Cells placed in isotonic solutions do not gain or lose H2O • Hypertonic • outside of cell has greater particle conc. • Cells placed in hypertonic solutions lose H2O and SHRINK • Hypotonic • inside of cell has greater conc. • Cells placed in hypotonic solutioins gain H2O and SWELL

  31. cell Osmosis in Hypertonic Medium Solute outside cell is greater water is drawn from inside the cell to outside solute 10% NaCl = hypertonic to blood cells (accustomed to 0.9%) CELL SHRINKS OR “CRENATES”

  32. Hypertonic solutions- shrink cells

  33. Osmosis in Hypotonic medium Solute inside cell is less and attracts water inside, causing swelling > 0.9 % NaCl = Hypotonic to blood cells CELL SWELLS

  34. Hypotonic solutions- swell cells Pressure on cell due to the flow of water is called OSMOTIC PRESSURE Check out the animation ---> click me

  35. Importance of Osmosis • Allows for absorption of H2O by the large intestine • Retention or shedding of H2O by kidneys • Uptake of H2O by the blood affects our blood pressure • Increased blood pressure creates a greater risk of heart attack and stroke • Watch these Flash Movies --->

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

  37. Endocytosis

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

  39. Exocytosis (Cellular Secretion)

  40. Movies! A wee flash tour of endocytosis and exocytosis – just click the image below

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

  42. 3 Types of Endocytosis • Click on active transport, then next a few times until the menu shows “endocytosis” • Phagocytosis = cell engulfs large amounts • Pinocytosis = the cell takes in (drinks) a small amount • Receptor-guided = when receptors must first be filled before endocytosis is allowed. This often happens with hormones.

  43. Three Types of Transport • Active Transport • requires energy ATP • Uses a transport protein in the membrane • Facilitated Transport = Passive • NO ATP necessary • Like active transport, uses a transport protein in the membrane • Diffusion and Osmosis = Passive • no ATP needed

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

  45. Active Transport Movement of particles low concentration into high concentration (against a concentration gradient) Requires energy input from ATP Cells use active transport to build up their stores of important particles, such as vitamins, minerals, salts, etc.

  46. Active TransportSodium-Potassium Pump • Balance of the two ions is done at same time • Helps to create a dipole inside and out of the cell • This is necessary for nerve cells to pass an electric impulse Click here to see a cool Flash Animation Na+ low Na+ high K+ low K+ high ATP required for maintenance of the pump

  47. Sodium-Potassium PumpClick image for an animation

  48. Types of Protein Transporters: Active Transport • carrier proteins • go against the concentration gradients Low to High • require Energy to function (ATP)

  49. Facilitated Diffusion • Proteins in the membrane assists in diffusion process • Solutes go from High conc to Low conc. Example: Glucose transporters Flash Animation http://bio.winona.msus.edu/berg/ANIMTNS/FacDiff.htm

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