Membrane Transport

• Passive diffusion


  Unassisted membrane transport
• Selective permeability

  • High concentration
  • Low concentration
  • Concentration gradient
• Assisted membrane transport


  • Passive transport
  • Active transport
• Protein channel


  • Ion channels
  • Lipid-free central passageway
  • Passive channels = always open
  • Highly selective
  • 0.8nm

  
• Aquaporins


  Protein channels
• Rate of osmosis too slow
• Protein channels


  • Gated channels
  • Controlling mechanism
  • conduction
  • Voltage-gated channels
  • Mechanically gated channels
  • Leakage channels
  • Ligand-gated channels
  • Conformational change
• Carrier-mediated transport


  • Facilitated diffusion
  • High specificity
  • Saturation
  • Transport maximum
• Active transport


  • Moves against concentration gradient
  • Requires energy
  • Primary active transport
  • Secondary active transport
• Sodium-Potassium pump


  • Generates cellular electrical activity
  • Na+/K+ ATPase pump

  
• Vesicular transport


  • Large molecules
  • Into cell
  • Out of cell