AS AQA Biology: Facilitated Diffusion and Active Transport

Facilitated Diffusion and Active Transport

Facilitated Diffusion

This is the transport of substances across a membrane by a trans-membrane protein molecule. These transport proteins are much like substrates and are so specific to one molecule so substances can only pass through a membrane if there is a protein molecule of the right type. This is a passive process and moves down the concentration gradient. Two types of transport protein:

• Channel Proteins: These form a water filled pore or channel in the membrane, which allows charged substances to diffuse across membranes. These can be gated to control the entry and exit.

• Carrier Proteins: These have a binding site specific to a particular molecule, it constantly flips between two states so it…