Facilitated diffusion does not require direct energy input from the cell (ATP) and proceeds down a concentration gradient, but it does rely on specific transmembrane proteins to move certain molecules across the membrane. In this sense, you can say that a facilitated diffusion process typically involves a particular transporter or channel that is specialized for a given molecule. Key points
- Yes, facilitated diffusion requires a specific transporter for a specific molecule: channel proteins or carrier proteins are usually selective for particular solutes, such as certain ions, sugars, or amino acids.
- How it works: the solute binds to the transporter on one side of the membrane, the transporter undergoes a conformational change (or provides a polar channel), and the solute is released on the other side, all without direct energy use by the solute or the cell.
- Distinction from simple diffusion: facilitated diffusion is saturable and dependent on transporter availability; the rate can plateau at high solute concentrations because transporters become occupied.
- Directionality: molecules move down their concentration gradient, from higher to lower concentration, unless a gradient is maintained by other cellular processes.
If you’d like, I can tailor this to a specific molecule (e.g., glucose via GLUT transporters, or a particular ion through an ion channel) and explain the exact transporter class, kinetics, and regulatory factors.
