Membrane Physiology

• Plasma membrane


  Outer boundary of every cell
• Plasma membrane


  • Selective permeability
  • No cell wall
  • Extremely thin layer of lipids and proteins

  
• Phospholipid bilayer


  • Polar
  • Non-polar
  • "Sandwich" appearance
• Hydrocarbon tails


  • Short & unsaturated = high permeability & fluidity
  • Long & saturated = low permeability & fluidity
• Cholesterol


  • Regulates membrane fluidity
  • Bidirectional regulator of fluidity
• Lipids


  • No bonds
  • Amphipathic
  • Steroid
  • Fused ring structure
  • Kinked tail
• High temperature


  Increases membrane fluidity
• Otis et al. (2011): 'Cholesterol and lipoprotein dynamics in a hibernating mammal'
• Fluid mosaic model


  Fluid lipid bilayer embedded with (integral) proteins and carbohydrates

  
• Osmosis


  Movement of water from high concentration to low concentration through a semipermeable membrane

  
• Passive diffusion


  Unassisted membrane transport
• Selective permeability


  • High concentration to low concentration
  • Concentration gradient
• Tonicity


  The response of cells or tissues immersed in the solution