Facilitated Diffusion: The Role of Channel Proteins
- While the phospholipid bilayer forms a barrier to most polar molecules and ions, specialized proteins called channel proteins enable the movement of these substances across the membrane.
- This process, known as facilitated diffusion, allows cells to control the exchange of essential substances without expending energy.
- Note that facilitated diffusion is still a form of passive transport, not active.
- But it uses channels to facilitate the diffusion.
Channel Proteins Are Integral Transmembrane Proteins
Definition
Channel protein
A specialized protein embedded in the membrane, allowing specific ions or molecules to diffuse across.
- Channel proteins have a pore that connects the cell's cytoplasm to the aqueous environment outside.
- Selective Pores: Each channel is highly specific, allowing only one type of particle to pass. For example:
- Sodium ions (Na⁺)
- Potassium ions (K⁺)
- Selective Pores: Each channel is highly specific, allowing only one type of particle to pass. For example:
- Its Determinants of Selectivity include:
- Pore Diameter: Ensures only appropriately sized molecules can pass.
- Chemical Properties: Attract specific ions while excluding others.
Facilitated diffusion through channel proteins is faster than simple diffusion because the hydrophilic interior of the channel reduces resistance to the movement of particles.
