Gefaciliteerd transport

Solutes like charged ions are repelled by the hydrophobic layer of the membrane, thereby halting diffusion. During the process of facilitated transport or facilitated diffusion, molecules can travel across the membrane via channels and carrier proteins that enable diffusion without requiring additional energy.

The first type, channel proteins, form a hydrophilic pore through which charged molecules can pass, thus avoiding the hydrophobic layer of the membrane. These channels are either always open or gated by some mechanism to control flow.

The second type, carriers, bind to a specific solute that changes the protein conformation, enabling the movement of solute down the gradient. For this reason, the rate of transport is not dependent on the concentration gradient, but rather on the number of carrier proteins available.

Even though it is more complex than simple diffusion, facilitated transport enables diffusion to occur at incredible rates, with channel proteins moving tens of millions of molecules a second and carrier proteins moving 1,000 to a million molecules a second.