4. Facilitated Diffusion and Active Transport

The large size of charged nature of some molecules prevents them from being able to move directly through a membrane. So facilitaed diffusion and active transport play a role...

Facilitated Diffusion:

• some larger molecules would take too long to diffuse through because they are so BIG.
• charged particles (ions) also diffuse slowly because they're water soluable, and the bilayer is hydrophobic so it would repel it.
  
• so to speed it up they diffuse through carrier proteins or channel proteins 
• like diffusion, facilitated diffusion moves down a concentration gradient, from a high to low concentration
• passive- no energy required 
• Carrier Proteins: move large molecules into or out of the cell, down the conc. gradient 
  • here's how they work:
    • a large molecule attaches to a carrier protein in…