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2B: CELL MEMBRANES

Beth Tonks Biology A-Level Englisch 76 Karten

2B: CELL MEMBRANES

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  1. 1CELL-SURFACE MEMBRANES (PLASMA MEMBRANE)Surround cells. A barrier between the cell and its environment, controlling which substances enter and leave the cell.
    Partially permeable - they let some molecules through but not others.
    Substances can move across the cell membrane by diffusion, osmosis or active transport.
  2. 2MEMBRANES WITHIN CELLSThe membranes around organelles divide the cell into different compartments - they act as a barrier between the organelle and the cytoplasm.
    e.g. the substances needed for respiration (e.g. enzymes) are kept together inside a mitochondria by the membrane surrounding the mitochondrion.
  3. 3MEMBRANES WITHIN CELLSThey are also partially permeable and control what substances enter and leave the organelle.
    e.g. RNA leaves the nucleus via the nuclear membrane (nuclear envelope) . DNA is too large to pass through the partially permeable membrane, so it remains in the nucleus.
  4. 4MEMBRANE STRUCTUREComposed of lipids (mainly phospholipids), proteins and carbohydrates (attached to proteins or lipids).
  5. 5MEMBRANE STRUCTURE: THE FLUID MOSAIC MODEL1972.
    Suggested to describe the arrangement of molecules in the membrane.
    In the model, phospholipid molecules form a continuous, double layer (bilayer).
  6. 6THE FLUID MOSAIC MODEL (2)Channel proteins and carrier proteins allow large molecules and ions to pass through membrane. Receptor proteins on CSA allow cell to detect chemicals released from other cells. Chemicals signal to the cell to respond in some way e.g. hormone insulin binds to receptor proteins on liver cells, tells cells to absorb glucose.
  7. 7THE FLUID MOSAIC MODEL (3)Some proteins are able to move sideways through the bilayer, while others are in fixed position.
    Some proteins have a carbohydrate attached - glycoproteins.
    Some lipids have a carbohydrate attached - glycolipids.
    Cholesterol molecules are also present.
  8. 8THE FLUID MOSAIC MODEL: WHY IS IT DESCRIBED AS 'FLUID' AND 'MOSAIC'?This bilayer is 'fluid' because the phospholipids are constantly moving.
    It's a mosaic as the proteins are scattered through the bilayer, like tiles in a mosaic. Include channel proteins and carrier PROTEINS
  9. 9THE FLUID MOSAIC MODELTHE FLUID MOSAIC MODEL
  10. 10MEMBRANE COMPONENTS: PHOSPHOLIPIDSForm a barrier to dissolved (water-soluble) substances.
    Have a hydrophilic head (attracts water) and a hydrophobic tail (repels water).
    Automatically arranges into a bilayer - heads face out towards the water on either side of the membrane.
  11. 11MEMBRANE COMPONENTS: PHOSPHOLIPIDS (2)Centre of bilayer is hydrophobic - membrane doesn't allow water-soluble substances (ions, polar molecules) to diffuse through it.
    Small, non-polar substances (e.g. carbon dioxide) and water can diffuse through the membrane.
  12. 12MEMBRANE COMPONENTS: PHOSPHOLIPIDSMEMBRANE COMPONENTS: PHOSPHOLIPIDS
  13. 13MEMBRANE COMPONENTS: CHOLESTEROLGives the membrane stability. A type of lipid present in all cell membranes (except bacterial). Fits between phospholipids. Binds to hydrophobic tails of phospholipids, causing them to pack more closely together - restricts movement of phospholipids, making membrane less fluid and more rigid.
  14. 14MEMBRANE COMPONENTS: CHOLESTEROL (2)Helps to maintain the shape of animal cells (don't have cell walls).
    Particularly important for cells that aren't supported by other cells e.g. red blood cells, which float free in the blood.
    Hydrophobic regions, so it's able to create a further barrier to polar substances moving through the membrane.
  15. 15MEMBRANE COMPONENTS: CHOLESTEROLMEMBRANE COMPONENTS: CHOLESTEROL
  16. 16TEMPERATURES AND MEMBRANES: BELOW 0Phospholipids don't have energy, so they can't move very much. Packed closely together and the membrane is rigid. Channel proteins and carrier proteins in the membrane denature, increasing the permeability of the membrane. Ice crystals may form and pierce the membrane, making it highly permeable when it thaws.
  17. 17TEMPERATURES AND MEMBRANES: 0 - 45The phospholipids can move around and aren't packed as tightly together - the membrane is partially permeable.
    As the temperature increases the phospholipids move more because they have more energy - this increases the permeability of the membrane.
  18. 18TEMPERATURES AND MEMBRANES: About 45Phospholipid bilayer starts to melt, membrane becomes more permeable.
    Water inside the cell expands, putting pressure on the membrane. Channel proteins and carrier proteins in membrane denature so they can't control what enters or leaves the cell - this increases the permeability of the membrane.
  19. 19TEMPERATURES AND MEMBRANESTEMPERATURES AND MEMBRANES
  20. 20REQUIRED PRACTICAL INVESTIGATING CELL MEMBRANE PERMEABILITYYou can investigate how different variables (e.g. temperature, solvent concentration) affect cell membrane permeability by doing experiments using beetroot.
    Beetroot cells contain a coloured pigment that leaks out - the higher the permeability of the membrane, the more pigment leaks out of the cell.
  21. 21REQUIRED PRACTICAL INVESTIGATING CELL MEMBRANE PERMEABILITYREQUIRED PRACTICAL INVESTIGATING CELL MEMBRANE PERMEABILITY
  22. 22—
  23. 23—
  24. 24—
  25. 25INVESTIGATING THE EFFECT OF SOLVENTSBeetroot to investigate effect of solvents on permeability of cell membranes i.e.placing beetroot cubes in different concentrations of solvent (alcohol, acetone). Surrounding cells in increasing concentrations increases membrane permeability - solvent dissolves lipids in membrane, causing it to lose structure.
  26. 26DEFINITION: DIFFUSIONThe net movement of particles from an area of higher concentration to an area of lower concentration.
  27. 27DIFFUSIONMolecules will diffuse both ways, but net movement will be to the area of lower concentration. Continues until particles are evenly distributed throughout liquid/gas. Down a concentration gradient. Passive process - particles can diffuse across cell membranes as long as they can move freely through the membrane.
  28. 28DEFINITION: CONCENTRATION GRADIENTThe path from an area of higher concentration to an area of lower concentration.
  29. 29DEFINITION: PASSIVE PROCESSNo energy is needed for it to happen.
  30. 30SIMPLE DIFFUSIONWhen molecules diffuse directly through a cell membrane.
    e.g. carbon dioxide and oxygen can diffuse through cell membranes- small so can pass through spaces between phospholipids. Non-polar, which makes them soluble in lipids, so they can dissolve in the hydrophobic layer.
  31. 31DIFFUSIONDIFFUSION
  32. 32FACTORS AFFECTING THE RATE OF DIFFUSION- Concentration gradient - higher=faster. Difference in concentration between the two sides decreases until it reaches an equilibrium and diffusion slows down over time.
    - Thickness of the exchange surface - thinner = faster, shorter diffusion pathway
    - Surface area - larger=faster
  33. 33FACTORS AFFECTING THE RATE OF DIFFUSION EXAMPLESSome specialised cells (e.g. epithelial cells in the small intestine) have microvilli - projections formed by the CSM folding up on itself.
    Microvilli give a larger surface area so more particles can be exchanged in the same amount of time - increasing the rate of diffusion.
  34. 34FACILITATED DIFFUSIONLarger molecules (e.g. amino acids, glucose) would diffuse slowly through phospholipid bilayer as they're too big.
    Charged particles (e.g. ions, polar molecules) would also diffuse slowly because they're water soluble, and the centre of the bilayer is hydrophobic.
    Diffuse through carrier/channel proteins.
  35. 35DEFINITION: FACILITATED DIFFUSIONThe passive movement of particles down a concentration gradient, from a higher to a lower concentration through the use of carrier proteins and channel proteins.
  36. 36FACILITATED DIFFUSION: CARRIER PROTEINSMove large molecules across membrane, down their concentration gradient. Different carrier proteins facilitate diffusion of different molecules.
    1 - Large molecule attaches to carrier protein in membrane. 2 - Protein changes shape. 3 - Releases molecule on opposite side of membrane.
  37. 37FACILITATED DIFFUSION: CARRIER PROTEINSFACILITATED DIFFUSION: CARRIER PROTEINS
  38. 38FACILITATED DIFFUSION: CHANNEL PROTEINSForm pores in the membrane for charged particles to diffuse through (down their concentration gradient)
    Different channel proteins facilitate the diffusion of different charged particles.
  39. 39FACILITATED DIFFUSION: CHANNEL PROTEINSFACILITATED DIFFUSION: CHANNEL PROTEINS
  40. 40FACTORS AFFECTING THE RATE OF FACILITATED DIFFUSION- Concentration gradient - higher=faster. As equilibrium is reacher, the rate of diffusion will level off.
    - Number of channel or carrier proteins - once all the proteins in a membrane are in use, facilitated diffusion can't happen any faster, even if you increase the concentration gradient.
  41. 41CALCULATING THE RATE OF DIFFUSION1. Draw a tangent at the time you want to find.
    2. Calculate the gradient of the tangent.
    gradient = change in y / change in x
    3. Find the units to give the rate of diffusion.
  42. 42CALCULATING THE RATE OF DIFFUSIONCALCULATING THE RATE OF DIFFUSION
  43. 43DEFINITION: OSMOSISThe diffusion of water molecules across a partially permeable membrane, from an area of higher water potential to an area of lower water potential.
  44. 44DEFINITION: WATER POTENTIALThe potential (likelihood) of water molecules to diffuse out of or into a solution.
  45. 45OSMOSISWater molecules - small, diffuse easily through the membrane. Large solute molecules can't. Pure water = wp of zero. Adding solutes to pure water lowers its wp - wp of any solution is always negative. The more negative the water potential, the stronger the concentration of solutes in solution.
  46. 46OSMOSISOSMOSIS
  47. 47ISOTONICTwo solutions have the same water potential. Cells in an isotonic solutions won't lose/gain any water - there's no net movement of water molecules because there's no different in water potential etween the cell and the surrounding solution.
  48. 48ISOTONICISOTONIC
  49. 49HYPOTONICIf a cell is placed in a solution that has a higher water potential it will swell as water moves into it by osmosis. Solutions with a higher water potential compared with the inside of the called are called hypotonic.
  50. 50HYPOTONICHYPOTONIC
  51. 51HYPERTONICIf a cell is placed in a solution that has a lower water potential it may shrink as water moves out of it by osmosis.
    Solutions with a lower water potential than the cell are called hypertonic.
  52. 52HYPERTONICHYPERTONIC
  53. 53FACTORS AFFECTING THE RATE OF OSMOSIS- Water potential gradient - higher = faster. As osmosis takes place, difference in water potential on either side of membrane decreases, so rate of osmosis levels off.
    - Thickness of the exchange surface - thinner = faster
    - Surface area of exchange surface - larger = faster
  54. 54REQUIRED PRACTICAL INVESTIGATING WATER POTENTIAL: MAKING SERIAL DILUTIONSA serial dilution is when you create a set of solutions that decrease in concentration by the same factor each time.
  55. 55REQUIRED PRACTICAL INVESTIGATING WATER POTENTIAL: MAKING SERIAL DILUTIONS EXAMPLEREQUIRED PRACTICAL INVESTIGATING WATER POTENTIAL: MAKING SERIAL DILUTIONS EXAMPLE
  56. 56REQUIRED PRACTICAL MEASURING CHANGE IN MASS1. Use cork borer to cut potatoes into identically sized chips, 1cm diameter. Divide into groups of 3. Measure mass of each group using mass balance.
    2. One group in each sucrose solution, 20 minutes.
    3. Remove chips, pat dry with paper towel. Weigh each group, record results. Calculate % change in mass for each group.
  57. 57DEFINITION: ACTIVE TRANSPORTThe movement of molecules and ions across plasma membranes, against a concentration gradient using carrier proteins and co-transporters.
    Uses energy.
  58. 58ACTIVE TRANSPORT: CARRIER PROTEINS1. Molecule attaches to carrier protein 2. Protein changes shape - moves molecule across membrane.
    3. Releases molecule on other side.
  59. 59ACTIVE TRANSPORT: CARRIER PROTEINSATP (produced by respiration) is a common source of energy in cells.
    Undergoes hydrolysis reaction, splitting into ADP and Pi (inorganic phosphate) - releases energy so solutes can be transported.
  60. 60ACTIVE TRANSPORT: CARRIER PROTEINSACTIVE TRANSPORT: CARRIER PROTEINS
  61. 61ACTIVE TRANSPORT: CO-TRANSPORTERSA type of carrier protein.
    Bind two molecules at a time.
    The concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient.
  62. 62MAIN DIFFERENCES BETWEEN ACTIVE TRANSPORT AND FACILITATED DIFFUSION- AT usually moves solutes from a low to high concentration - FD is high to low concentration
    - AT requires energy - FD does not
  63. 63ACTIVE TRANSPORT: CO-TRANSPORTERS EXAMPLECo-transport of sodium ions and glucose. Sodium ions move across the membrane down their concentration gradient. This moves glucose across the membrane too, against its concentration gradient.
  64. 64ACTIVE TRANSPORT: CO-TRANSPORTERS EXAMPLEACTIVE TRANSPORT: CO-TRANSPORTERS EXAMPLE
  65. 65CO-TRANSPORT AND THE ABSORPTION OF GLUCOSEGlucose is absorbed into the bloodstream in the small intestine.
    In the mammalian ileum the concentration of glucose is too low for glucose to diffuse out into the blood so it is absorbed from the lumen of the ileum by co-transport.
  66. 66CO-TRANSPORT AND THE ABSORPTION OF GLUCOSE STEP 1Sodium ions are actively transported out of the epithelial cells in the ileum, into the blood, by the sodium-potassium pump.
    This creates a concentration gradient - now a higher concentration of sodium ions in the lumen of the ileum than inside the cell.
  67. 67CO-TRANSPORT AND THE ABSORPTION OF GLUCOSE STEP 1CO-TRANSPORT AND THE ABSORPTION OF GLUCOSE STEP 1
  68. 68CO-TRANSPORT AND THE ABSORPTION OF GLUCOSE STEP 2This causes sodium ions to diffuse form the lumen of the ileum into the epithelial cell, down their concentration gradient via the sodium-glucose co-transporter proteins.
    The co-transporter carries glucose into the cell with the sodium. The concentration of glucose inside the cell increases.
  69. 69CO-TRANSPORT AND THE ABSORPTION OF GLUCOSE STEP 2CO-TRANSPORT AND THE ABSORPTION OF GLUCOSE STEP 2
  70. 70CO-TRANSPORT AND THE ABSORPTION OF GLUCOSE STEP 3Glucose diffuses out of the cell, into the blood, down its concentration gradient through a protein channel, by facilitated diffusion.
  71. 71CO-TRANSPORT AND THE ABSORPTION OF GLUCOSE STEP 3CO-TRANSPORT AND THE ABSORPTION OF GLUCOSE STEP 3
  72. 72FACTORS AFFECTING THE RATE OF ACTIVE TRANSPORT- Speed of individual carrier proteins - faster=faster
    - Number of carrier proteins present - more=faster
    - Rate of respiration and availability of ATP - if respiration is inhibited, active transport can't take place.
  73. 73SUMMARY OF DIFFUSIONNet movement of particles from an area of higher concentration to an area of lower concentration.
    Passive process - doesn't require energy.
  74. 74SUMMARY OF FACILITATED DIFFUSIONNet movement of particles from an area of higher concentration to an area of lower concentration.
    Uses carrier proteins and channel proteins to aid the diffusion of large molecules and charged particles through the membrane.
    Passive process - doesn't require energy.
  75. 75SUMMARY OF OSMOSISMovement of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential.
    Passive process - doesn't require energy.
  76. 76SUMMARY OF ACTIVE TRANSPORTMovement of molecules, usually from an area of lower concentration to an area of higher concentration.
    Uses carrier proteins and co-transporters to transport molecules.
    Active process - requires energy.

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A-Level Biology (UNIT 2) Karteikarten am 2B: CELL MEMBRANES, erstellt von Beth Tonks am 06/04/2016.
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