Tang 06 transport across membranes

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Tang 06 transport across membranes

  1. 1. TRANSPORT ACROSS MEMBRANES
  2. 2. TRANSPORT ACROSS MEMBRANES Three categories Passive transport i) Simple diffusion ii) Facilitated diffusion iii) Osmosis Active transport 1) Primary active transport 2) Secondary active transport Exocytosis/endocytosis
  3. 3. TRANSPORT ACROSS MEMBRANES Membrane permeability: Permeable Lets most substances through Selectively/differentially permeable Lets specific substances through Impermeable Does not let substances through
  4. 4. PASSIVE TRANSPORT
  5. 5. PASSIVE TRANSPORT Passive transport: Movement of substance across a membrane without using energy Passive transport relies on diffusion and concentration gradients.
  6. 6. PASSIVE TRANSPORT Diffusion: Substances move from areas of high concentration to areas of low concentration. Eventually a dynamic equilibrium is reached where the concentrations are continuously balanced
  7. 7. PASSIVE TRANSPORT Dynamic equilibrium: Ions/substances continue to move from one region to another, but there is no net change in concentration.
  8. 8. PASSIVE TRANSPORT i) Simple diffusion: Some substances cross a membrane unassisted. Their ability to diffuse depends on size, polarity, and charge.
  9. 9. PASSIVE TRANSPORT i) Simple diffusion:
  10. 10. PASSIVE TRANSPORT i) Simple diffusion:
  11. 11. PASSIVE TRANSPORT i) Simple diffusion: Size: Small Polarity (charge): Non-polar (uncharged) Examples: O2, CO2 Rate of diffusion: Fast Explanation: Readily soluble in the hydrophobic interior of the bilayer. CO2 CO2 O2 O2
  12. 12. PASSIVE TRANSPORT i) Simple diffusion: Size: Moderate to large Polarity (charge): Non-polar (uncharged) Examples: Steroids, non-polar drugs Rate of diffusion: Fast Explanation: Readily soluble in the hydrophobic interior of the bilayer.
  13. 13. PASSIVE TRANSPORT i) Simple diffusion: Size: Small Polarity (charge): Polar (uncharged) Examples: H2O, glycerol Rate of diffusion: Fast Explanation: Their small size easily crosses the hydrophobic membrane H2O
  14. 14. PASSIVE TRANSPORT i) Simple diffusion: Size: Moderate to large Polarity (charge): Polar (uncharged) Examples: Glucose, sucrose Rate of diffusion: Very, very slow (impermeable) Explanation: Their large size and polarity prevent them from crossing the membrane
  15. 15. PASSIVE TRANSPORT i) Simple diffusion: Size: Any size Polarity (charge): Charged (ions) Examples: Na+, K+, Mg2+, Ca2+ Rate of diffusion: Very, very slow (impermeable) Explanation: Their charge prevents them from crossing the non-polar interior Na+ Mg2+
  16. 16. PASSIVE TRANSPORT ii) Facilitated diffusion: Diffusion helped by transport proteins (2 kinds) Channel proteins Carrier proteins How can important large polar molecules and ions be transported across the membrane?
  17. 17. PASSIVE TRANSPORT ii) Facilitated diffusion: Channel protein: Forms a hydrophilic pathway for polar molecules and ions.
  18. 18. PASSIVE TRANSPORT ii) Facilitated diffusion: Channel protein: Some ion channels are voltage-gated; they have opened, closed, and intermediate states depending on the voltage
  19. 19. PASSIVE TRANSPORT ii) Facilitated diffusion: Carrier protein: Binds to a molecule and transports it across membrane through a conformational (shape) change.
  20. 20. PASSIVE TRANSPORT ii) Facilitated diffusion: Transport proteins speed up the diffusion of substrates across membranes, although it reaches a maximum rate. What limits the rate? The number of transport proteins available
  21. 21. PASSIVE TRANSPORT ii) Facilitated diffusion: Transport proteins are often very selective about the solutes they will carry (i.e. glucose transporter will not transport fructose). Specific to one kind of substrate
  22. 22. PASSIVE TRANSPORT Comparing simple and facilitated diffusion: Facilitated diffusion
  23. 23. PASSIVE TRANSPORT iii) Osmosis: Passive diffusion of water Water can diffuse into and out of cells based on concentration of solute inside and outside a cell.
  24. 24. PASSIVE TRANSPORT iii) Osmosis: Water can move in or out of a cell, causing it to expand or shrink, based on the type of solution it is placed in: Hypotonic – lower solute concentration outside the cell Isotonic – same solute concentration outside the cell Hypertonic – higher solute concentration outside the cell
  25. 25. PASSIVE TRANSPORT iii) Osmosis: A hypotonic solution can swell an animal cell to the point of lysis, but plant cells have cell walls to prevent this.
  26. 26. PASSIVE TRANSPORT iii) Osmosis: Identify the type of solution that the red blood cells are placed in:
  27. 27. ACTIVE TRANSPORT
  28. 28. ACTIVE TRANSPORT Active transport: Movement of substances across a membrane using energy against concentration gradient. Requires protein “pumps”.
  29. 29. ACTIVE TRANSPORT 1) Primary active transport: Moves positively charged ions (i.e. H+, Ca2+, Na+, K+). i.e. H+ pump (a.k.a. proton pump)
  30. 30. ACTIVE TRANSPORT 1) Primary active transport - H+ pump (a.k.a. proton pump) Step 1) Transport protein hydrolyses ATP. Phosphate group binds to protein and changes the protein’s conformation. Protein can now bind to H+ ion. H H+ H+ H+ H+ H+
  31. 31. ACTIVE TRANSPORT 1) Primary active transport - H+ pump (a.k.a. proton pump) Step 2) H+ ion binds to protein, causing a conformational change, which also weakens the binding of the H+ ion. H+ H+ H+ H+ H+ H+ H+ H+
  32. 32. H+ ACTIVE TRANSPORT 1) Primary active transport - H+ pump (a.k.a. proton pump) Step 3) H+ ion is released to side of higher concentration. Phosphate is also released. H+ H+ H+ H+ H+
  33. 33. ACTIVE TRANSPORT 1) Primary active transport - H+ pump (a.k.a. proton pump) Step 4) Release of H+ and phosphate returns the protein to its original conformation. H+ H+ H+ H+ H+ H+ Unequal concentrations of ions on both sides of a membrane creates an electrochemical gradient.
  34. 34. ACTIVE TRANSPORT 1) Primary active transport Electrochemical gradient: Often involved in transmitting nervous impulses
  35. 35. ACTIVE TRANSPORT 1) Primary active transport: Sodium-potassium pump: 2 ions pumped at once in opposite directions. Drives most secondary active transport. -3 Na+ ions pumped out -2 K+ ions are pumped in
  36. 36. ACTIVE TRANSPORT The sodium-potassium pump is an example of antiport. Symport: solute moves through membrane in the same direction as driving ion Antiport: solute moves through membrane in opposite direction as driving ion
  37. 37. ACTIVE TRANSPORT 2) Secondary active transport: Uses the concentration gradient of an ion as its energy source. Often coupled with a primary active transport pump which creates a concentration gradient.
  38. 38. ACTIVE TRANSPORT 2) Secondary active transport: i.e. Glucose transporter: Uses sodium to transport glucose into cell
  39. 39. PASSIVE VS. ACTIVE TRANSPORT Comparing passive and active transport:
  40. 40. ENDOCYTOSIS & EXOCYTOSIS
  41. 41. ENDOCYTOSIS & EXOCYTOSIS To transport larger molecules that pumps/channels cannot transport, cells use endocytosis and exocytosis which requires vesicles and energy. Endocytosis: Import into the cell Exocytosis: Export out of the cell
  42. 42. ENDOCYTOSIS Endocytosis: 3 kinds 1) Bulk-phase endocytosis: Also known as pinocytosis (“cell drinking”). Extracellular water and substances are taken in.
  43. 43. ENDOCYTOSIS Endocytosis: 3 kinds 1) Bulk-phase endocytosis: Also known as pinocytosis (“cell drinking”). Extracellular water and substances are taken in.
  44. 44. ENDOCYTOSIS Endocytosis: 3 kinds 2) Receptor-mediated endocytosis: Receptors on cell surface bind to substance before intake. Clathrin proteins form a pit which aid the formation of a vesicle. Vesicle may fuse with lysosome for digestion.
  45. 45. ENDOCYTOSIS Endocytosis: 3 kinds 2) Receptor-mediated endocytosis: Receptors on cell surface bind to substance before intake. Clathrin proteins form a pit which aid the formation of a vesicle. Vesicle may fuse with lysosome for digestion.
  46. 46. ENDOCYTOSIS Endocytosis: 3 kinds 3) Phagocytosis: Cell engulfs bacteria, parts of dead cells, viruses, and other foreign particles. Macrophages (white blood cells) in the immune system use phagocytosis to engulf pathogens.
  47. 47. ENDOCYTOSIS Endocytosis: 3 kinds 3) Phagocytosis: Cell engulfs bacteria, parts of dead cells, viruses, and other foreign particles. Macrophages (white blood cells) in the immune system use phagocytosis to engulf pathogens.
  48. 48. EXOCYTOSIS Exocytosis: Secretory vesicles fuse with plasma membrane to release contents outside of cell. Used for secreting materials like hormones and enzymes.
  49. 49. EXOCYTOSIS Exocytosis: Secretory vesicles fuse with plasma membrane to release contents outside of cell. Used for secreting materials like hormones and enzymes.

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