facilitated diffusion

• larger molecules and charged particles would diffuse very slowly through the membrane, so they diffuse via facilitated diffusion, through channel or carrier proteins
• particles still move down a concentration gradient - higher to lower
• passive process
• charged particles are water-soluble, and the centre of the bilayer is hydrophobic
• carrier proteins move large molecules across membranes
• different carrier proteins facilitate the diffusion of different molecules
• carrier proteins - a molecule attaches to the protein at a binding site. this causes the protein to change shape, which releases the molecule on the other side of the membrane
• channel proteins - form pores in the membrane for the charged molecules to diffuse through. different channel proteins facilitate the diffusion of different particles