2.17 Facilitated Diffusion

Facilitated diffusion

the passive movement of molecules or ions down a concentration gradient across a cell membrane, through transmembrane proteins (channel or carrier proteins)

Hydrophilic substances diffuse…

across the cell membrane (via protein molecules)

• don’t interact with the hydrophilic centre

Carrier proteins

• binding site (for a specific chemical)

• chemical binds → tertiary structure of CP changes → brings chemical across membrane → chemical released

Channel proteins

• selective (only certain chemicals can pass through each protein channel)

• some always open, some trigger response (eg chemical binding to it, change in voltage across membranes)

• central pore lined w hydrophilic amino acids + contains water

• hydrophilic substances can pass through channel