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MEMBRANE STRUCTURE AND TRAFFIC

MEMBRANE STRUCTURE AND TRAFFIC. Membrane Models. General Features of the Plasma Membrane A boundary that separates living cell from nonliving environment. A control device for chemical traffic into and out of the cell. Is selectively permeable .

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MEMBRANE STRUCTURE AND TRAFFIC

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  1. MEMBRANE STRUCTURE AND TRAFFIC AP Biology

  2. Membrane Models General Features of the Plasma Membrane • A boundary that separates living cell from nonliving environment. • A control device for chemical traffic into and out of the cell. • Is selectively permeable. • Has a unique structure which determines its function and solubility characteristics. • Intimately involved in cell cell recognition. AP Biology

  3. Membrane Models A. Early Membrane Observations 1. Lipid and lipid soluble materials enter cells more rapidly than substances that are insoluble in lipids. • Deduction: Membranes are made of lipids. • Deduction: Fat-soluble substance move through the membrane by dissolving in it ("like dissolves like"). AP Biology

  4. Membrane Models A. Early Membrane Models 2. Evidence: Amphipathic phospholipids will form an artificial membrane on the surface of water with only the hydrophilic heads immersed in water • Amphipathic = Condition where a molecule has both a hydrophilic region and a hydrophobic region. • Deduction: Because of their molecular structure, phospholipids can form membranes. They form either layers or micelles. AP Biology

  5. CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3 O CH2 H3C N O P O CH2 O CH CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 O HC O C CH O H2C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 tails (hydrophobic) head (hydrophilic)

  6. extracellular fluid (watery environment) phospholipid hydrophilic heads hydrophobic tails bilayer hydrophilic heads cytoplasm (watery environment)

  7. Membrane Models A. Early Membrane Observation 3. Phospholipid content of membranes isolated from red blood cells is just enough to cover the cells with two layers. • Deduction: Cell membranes are actually phospholipid bilayers, two molecules thick. 4. Membranes isolated from red blood cells contain proteins as well as lipids. • There is protein in biological membranes. AP Biology

  8. Membrane Models B. The Davson-Danielli Model (1935) • Phospholipid bilayer sandwiched between two layers of globular protein. • Polar heads are oriented towards protein layers forming a hydrophilic zone. • Nonpolar tails are oriented in between polar heads forming a hydrophobic zone. AP Biology

  9. Membrane Models B. The Davson-Danielli Model • Not all membranes are identical or symmetrical. • Membranes with different functions also differ in chemical composition and structure. • Membranes are bifacial with distinct inside and outside faces. • A membrane with an outside layer of proteins would be an unstable structure. • Membrane proteins are not soluble in water, and, like phospholipid, they are amphipathic. • Protein layer not likely because its hydrophobic regions would be in an aqueous environment, and it would also separate the hydrophilic phospholipid heads from water. AP Biology

  10. Membrane Models C. The Singer-Nicolson Model (1972) AP Biology

  11. Membrane Models D. The Fluid Mosaic Model 1. Membranes are Fluid AP Biology

  12. Membrane Models D. The Fluid Mosaic Model • Membranes are Fluid • Membranes are Mosaics of Structure and Function AP Biology

  13. Membrane Models D. The Fluid Mosaic Model • Membranes are Fluid • Membranes are Mosaics of Structure and Function • Membranes are bifacial. AP Biology

  14. Membrane Models D. The Fluid Mosaic Model • Membranes are Fluid • Membranes are Mosaics of Structure and Function • Membranes are bifacial. • Membrane Carbohydrates recognize other cells. AP Biology

  15. Membrane Models D. The Fluid Mosaic Model 2. Membrane proteins drift more slowly than lipids. The fact that proteins drift laterally was established experimentally by fusing a human and mouse cell: • Membrane proteins of a human and mouse cell were labeled with different green and red fluorescent dyes. • Cells were fused to form a hybrid cell with a continuous membrane. • Hybrid cell membrane had initially distinct regions of green and red dye. • In less than an hour, the two colors were intermixed. AP Biology

  16. Membrane Models D.The Fluid Mosaic Model 3. Some membrane proteins are tethered to the cytoskeleton and cannot move far. 4. Membranes solidify if the temperature decreases to a critical point. Critical temperature is lower in membranes with a greater concentration of unsaturated phospholipids. AP Biology

  17. Membrane Models D. The Fluid Mosaic Model 5. Because they hinder close packing of phospholipids, the steroid cholesterol and unsaturated hydrocarbon tails (with kinks at the carbon-to-carbon double bonds) enhance membrane fluidity. 6. Membranes must be fluid to work properly. Solidification may result in permeability changes and enzyme deactivation. 7. Organisms adapt to cold temperatures by altering membrane lipid composition (e.g. winter wheat increases concentration of membrane unsaturated phospholipids and some hibernating animals enrich membranes with cholesterol). AP Biology

  18. Extracellular Fluid (outside) glycoprotein binding site phospholipid bilayer phospholipid carbohydrate cholesterol receptor protein transport protein protein filaments recognition protein Cytoplasm (inside)

  19. drop of dye water molecule

  20. drop of dye water molecule

  21. drop of dye water molecule

  22. 4.2 How Do Substances Move Across Membranes? • 4.2.2 Movement Across Membranes Occurs by Both Passive and Active Transport • Table 4.1 Transport Across Membranes (p. 62) AP Biology

  23. 4.2 How Do Substances Move Across Membranes? • 4.2.3 Passive Transport Includes Simple Diffusion, Facilitated Diffusion, and Osmosis • 4.2.3.1 Plasma Membranes Are Selectively Permeable to Diffusion of Molecules • 4.2.3.2 Some Molecules Move Across Membranes by Simple Diffusion • Figure 4.3 (Hide/Reveal) Diffusion through the plasma membrane (p. 63) AP Biology

  24. Simple diffusion Facilitated diffusion through a channel (extracellular fluid) lipid-soluble molecules (O2, CO2, H2O) ions channel protein (cytoplasm) Facilitated diffusion through a carrier (extracellular fluid) amino acids, sugars, small proteins carrier protein (cytoplasm)

  25. Simple diffusion (extracellular fluid) lipid-soluble molecules (O2, CO2, H2O) (cytoplasm)

  26. Facilitated diffusion through a channel ions channel protein

  27. Facilitated diffusion through a carrier amino acids, sugars, small proteins (extracellular fluid) carrier protein (cytoplasm)

  28. Facilitated diffusion through a carrier (extracellular fluid) amino acids, sugars, small proteins carrier protein (cytoplasm)

  29. Facilitated diffusion through a carrier amino acids, sugars, small proteins carrier protein

  30. amino acids, sugars, small proteins

  31. 4.2 How Do Substances Move Across Membranes? • 4.2.3.3 Other Molecules Cross the Membrane by Facilitated Diffusion, with the Help of Membrane Transport Proteins • 4.2.3.4 Osmosis Is the Diffusion of Water Across Membranes • Figure 4.4 Osmosis (p. 64) AP Biology

  32. H2O selectively permeable membrane sugar pore selectively permeable membrane sugar molecule water molecule

  33. H2O selectively permeable membrane sugar pore

  34. selectively permeable membrane sugar molecule water molecule

  35. 4.2 How Do Substances Move Across Membranes? • 4.2.3.5 Osmosis Across the Plasma Membrane Plays an Important Role in the Lives of Cells • Figure 4.5 The effects of osmosis (p. 65) AP Biology

  36. 10 micrometers Hypertonic solution Hypotonic solution Isotonic solution

  37. 10 micrometers Isotonic solution

  38. Hypertonic solution

  39. Hypotonic solution

  40. 4.2 How Do Substances Move Across Membranes? • 4.2.4 Active Transport Uses Energy to Move Molecules Against Their Concentration Gradients • Figure 4.6 (Hide/Reveal) Active transport (p. 66) AP Biology

  41. (extracellular fluid) Energy from ATP changes the shape of the transport protein and moves the ion across the membrane. 2 The transport protein binds both ATP and Ca2+. 1 The protein releases the ion and the remnants of ATP (ADP and P) and closes. 3 ADP recognition site P ATP ATP binding site Ca2+ (cytoplasm)

  42. (extracellular fluid) 1 Energy from ATP changes the shape of the transport protein and moves the ion across the membrane. 2 The protein releases the ion and the remnants of ATP (ADP and P) and closes. 3 The transport protein binds both ATP and Ca2+. ADP ATP binding site recognition site P ATP (cytoplasm) Ca2+

  43. (extracellular fluid) 1 The transport protein binds both ATP and Ca2+. ATP binding site recognition site ATP Ca2+ (cytoplasm)

  44. (extracellular fluid) Energy from ATP changes the shape of the transport protein and moves the ion across the membrane. 2 (cytoplasm)

  45. (extracellular fluid) The protein releases the ion and the remnants of ATP (ADP and P) and closes. 3 ADP P (cytoplasm)

  46. 4.2 How Do Substances Move Across Membranes? • 4.2.5 Cells Engulf Particles or Fluids by Endocytosis • Figure 4.7 Three types of endocytosis (p. 67) AP Biology

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