Channel proteins facilitate the diffusion of ions and molecules down their concentration gradient across the membrane. These proteins are characterised by being open to both the intracellular and extracellular space of the cell at the same time. Because the substance being transported is moving down its concentration gradient, the process of facilitated diffusion does not require energy, it is a passive process. These proteins can be highly specific and only transport a certain molecule or solute. This specificity is acquired from the channels charge, shape and size. The protein can also change the uptake of a molecule due to the conditions outside the cell such as pH. The molecules to be transported form a line and move simultaneously at a rapid rate (108 per second).
- ↑ Harvey Lodish, Arnold Berk, S Lawrence Zipursky, Paul Matsudaira, David Baltimore, and James Darnell. New York: W. H. Freeman; 2000.