Cell Membrane + Transport

• Cell Membrane


  • Allows materials to move in and out of the cell
  • Contains phospholipids in a double layer that is embedded with proteins and other molecules (which is why it is called a phospholipid bilayer)
• Roles of Membrane Proteins


  • Join with other cells
  • Enzymic activity
  • Transport
  • Recogize cells
  • Attatch with things
  • Transduction (converting energy into another form)

  JETRAT
• Transportation Across Cell Membrane

  • The cell membrane is semi-permeable (only certain things can enter)
  • Selective Transport- movement of molecules across the cell membrane to maintain concentration gradients (high to low)
  • Can be passive (no energy required) or active (requires energy)
• Passive Transport

  Three types:

  • Diffusion - movement of solutes from high to low concentration
  • Osmosis - movement of water from high to low
  • Facilitated diffusion - same as diffusion but with help of transport proteins
• Cell Surface Area:Volume Ratio


  As cells get larger, they need more surface area to absorb enough nutrients and molecules

  • formula: SA/V
• Phospholipids

  • always have heads and tails
  • head is hydrophilic (loves water)
  • tail is hydrophobic (hates water)

  
• Membrane Models

  • Trilaminar Model (Davidson and Danielli) - protein layers sandwich lipid layer
  • Fluid Mosaic (Singer and Nicolson) - proteins embedded in phospholipid layer

  
• Membrane Proteins

  • proteins physically transport substances across the membrane and carry our chemical reactions
  • Integral - permanently embedded
  • Peripheral - attached to surface

  
• Cholesterol


  Type of lipid in cell membrane that helps maintain fluidity to maintain cell integrity and prevent entry of unwanted molecules that aren't water-soluable

  
• If the cell doesn't maintain a concentration gradiant, then this will happen:

  • Hypertonic- more water outside than inside (shrinks)
  • Hypotonic- more water inside than outside (bloats)

  If it's normal then this happens:

  • Isotonic- equal amounts of water inside and outside

  
• Active Transport

  • Requires energy to move molecules against concentration gradient (low to high)

  Three types:

  • Endocytosis- takes in insoluable or large molecules
  • Exocytosis- releases insoluable or large molecules
  • Sodium-Potasium pump- A protein that dumps 3 sodium ions out the cell for every 2 potasium ions pulled in

  
• Endocytosis


  Two Types:

  • pinocytosis- takes in fluids + solute (cell drinking)
  • phagocytosis- takes in larger substances (cell eating)