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Cell membrane and cell membrane transport


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IB Biology class 1.3,1.4

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Cell membrane and cell membrane transport

  1. 1. Membranes & Movements Across Them. Topic 1.3, 1.4
  2. 2. Cell membranes surround us.. Cell membranes enclose the cell and most of the organelles. They have the same structure.
  3. 3. The basic unit of construction  The phospholipid
  4. 4. What do they look like?  Model 1: Danielli –Davson  Describe what you see…
  5. 5. Singer – Nicholson Fluid Mosaic Model  Model 2: Singer-Nicolson  Describe what you see…
  6. 6. Fluid mosaic model:  Phospholipid bilayer  Phosphate head  Hydro?  Two lipid tails  Hydro?  Integral proteins (pass through the membrane)  Peripheral proteins (embedded on the outside)  Glycoproteins (combination of protein and carbohydrate)  Glycolipids (combination of protein and lipid)
  7. 7. Protein functions  Hormone Binding Site: On surface. Allows one type of hormone to bind. Triggers signal to inside of cell.  Enzymes: either catalyse reactions inside or outside the cell, depending on location of active site.  Electron Carriers: arranged in chains so electrons can be passed along.  Cell adhesion  Channels for Passive Transport: allow a specific substance to pass through middle of protein.  Pumps for Active Transport: release energy from ATP to move specific substances across the membrane.
  8. 8. Transport across membranes Passive, active and (active) by vesicles
  9. 9. Passive Does not require cellular energy
  10. 10. Active Requires cellular energy
  11. 11. Diffusion  Diffusion is Passive (no energy required)  Net movements with (along) concentration gradient  Particles from high conc  low conc  Hypertonic  hypotonic  Simple diffusion: some particles (small un- charged like Oxygen)  Facilitated diffusion: channel proteins
  12. 12. Facilitated vs. Active transport • Active transport happens against the concentration gradient, and requires energy in the form of ATP • Facilitated diffusion happens down the concentration gradients, and requires no energy. • Both occur through integral protein channels!
  13. 13. Osmosis  Passive movement of water  Net movements  From low solute conc  high solute conc  Hypotonic  hypertonic  High water potential  Low water potential Solute: that which is dissolved in a solvent (water)
  14. 14. Active transport  Moves substances against the concentration gradient  Protein pumps for particular substances  Uses energy from ATP (adenosine triphosphate)
  15. 15. Transport by vesicles (both made possible by fluidity of membrane)  Endocytosis  Membrane pulls in  Vesicle forms  Droplet taken in  ‘Cell drinking’  Exocytosis  Protein from ribosome to rER  Vesicle buds off rER; go to Golgi Apparatus  GA buds off  Vesicle moves to membrane  Fuses  Protein expelled
  16. 16. Exocytosis Vesicle moves to membrane, and fuses with the plasma membrane, expelling the contents eg. A digestive enzyme
  17. 17. Endocytosis
  18. 18. Phagocytosis  The same as Pinocytosis but a solid particle is ingested, instead of a liquid.  White blood cells (Phagocytes) ingest pathogens
  19. 19. Sodium – Potassium Pump
  20. 20. Membrane of a neurone  Sodium ions are pumped out, potassium ions pumped in. The channel proteins are closed  The membrane is poised for action  As soon as the channels open, the ions will flood in by: what process?  -Facilitated diffusion
  21. 21. Nerve transmission (Sodium floods back in)
  22. 22. Organ transplants: Mind the osmolarity!  Organs which are being used for medical procedures eg. Heart transplants, need to be bathed in an isotonic solution.  Why? Image credit