Write short notes on facilitated diffusion.

Explanation

1) Membrane protein provides sites at which certain molecules can cross the membrane. This process is called facilitated diffusion.
2) Porins are proteins that form huge pores in the outer membranes of the plastids, mitochondria and some bacteria, allowing molecules up to the size of small proteins to pass through.
3) Concentration gradient must already be present for molecules to diffuse even if facilitated by the proteins.
4) In facilitated diffusion, special proteins help to move substance across the membrane without expenditure of ATP energy.
5). Facilitated diffusion cannot cause net transport of molecules from a low to a high concentration this would require input of energy.
6) Transport rate reaches a maximum when all of the protein transporters are being used.
7) Facilitated diffusion is very specific, it allows cell to select substance for uptake.
8) It is sensitive to inhibitors which react with protein side chain.