Facilitated Diffusion

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In facilitated diffusion a protein (shown in green)serves as a channel for diffusing molecules(red) that otherwise would not be able to pass through the cell membrane. The molecule changes shape to accommodate a particular type of molecule. The only energy involved is kinetic energy from the moving molecules. The proteins involved in facilitated diffusion are not actively pumping the molecules through. Some of these proteins are called gated proteins because they can allow the molecule through at certain times but not others. For example in a neuron a special gated protein allows sodium ions to enter the neuron when the neuron is stimulated.

Note! that since facilitated diffusion is simply diffusion involving a protein to make diffusion happen more easily across a cell membrane, this process cannot concentrate substances in a cell beyond that in the surrounding environment.


created 7/9/99 revised 1/04/00