bio 5

• Cell membrane function


  Selectively permeable barrier that separates the inside of a cell from the outside (intracellular and extracellular)
• Cell membrane structure


  Phospholipid bilayer with proteins, cholesterol, glycoproteins, glycolipids, steroids

  
• Fluid mosaic model


  Membrane components are capable of lateral diffusion, membranes are composed of various phospholipids, proteins, cholesterol, glycoproteins, glycolipids, steroids

  
• Cell membrane components


  Phospholipids, proteins, cholesterol

  
• Membrane proteins


  • Peripheral (not embedded, easy to remove, lacks hydrophobic amino acid sequences)
  • Integral (transmembrane, difficult to remove, hydrophobic regions interact with interior of membrane)
• Membrane cholesterol


  Keeps membranes from becoming too fluid as temperature increases and too rigid when temps decrease
• Selective permeability of cell membrane

  • Hydrophobic molecules (lipids, O2, CO2) can dissolve in and cross with ease
  • Small, polar molecules (H2O, ethanol) can pass between phospholipids
  • Large, polar molecules (glucose, amino acids) do not cross
  • Ions (K+, Na+, Cl-, Ca2+) do not cross

  
• Membrane transport


  1. Diffusion (passive, no energy required, down concentration gradient)

  2. Facilitated diffusion (passive, requires channel/carrier protein, down concentration gradient)

  3. Active transport (requires energy, against concentration gradient)
• Na+/K+ ATPase pump


  Example of active transport, pumps Na+ out and K+ into the cell against their concentration gradients
• Hydrophobic molecules


  Can dissolve in and cross membranes with ease
• Small, polar molecules


  Can pass between phospholipids
• Large, polar molecules and ions

  Do not cross the membrane
• Osmosis


  Passive diffusion of water across a semi-permeable membrane, depends on solute concentration
• Hypertonic solution


  Has a higher relative solute concentration than the cell
• Hypotonic solution


  Has a lower relative solute concentration than the cell
• Isotonic solution


  Has the same relative solute concentration as the cell
• Hypertonic solution


  Water flows out of the cell, cell shrivels
• Hypotonic solution


  Water flows into the cell, cell enlarges until it bursts
• Isotonic solution


  Cell is normal, no net water flow
• Phagocytosis


  Plasma membrane engulfs a particle, membrane pinches off and forms a vacuole containing the particle
• Pinocytosis


  Plasma membrane engulfs small amounts of extracellular fluid, forming small vesicles
• Phagocytosis is similar to vesicle budding