facilitated diffusion

• facilitated diffusion transports large, polar molecules across the cell membrane by protein molecules
• the protein molecules are channel and carrier proteins
• facilitated diffusion transports ions/polar molecules from a region of higher concentration to a region of lower concentration
• facilitated diffusion is a passive process so does not require energy
• carrier and channel proteins are both intrinsic membrane proteins
• the number of proteins in the membrane can affect the rate of diffusion
• carrier proteins:

  • molecule binds to the binding site (complimentary to molecule)
  • protein's tertiary structure changes
  • molecule released on the other side of the membrane
• channel proteins:

  • pore is lined with hydrophilic amino acids and contains water
  • hydrophilic substances can move through channel proteins
• channel proteins are selective - only certain molecules can pass through each type of protein