Overview
This lecture explains facilitated diffusion, focusing on how special protein carriers assist specific molecules in crossing cell membranes without energy input.
Facilitated Diffusion Process
- Facilitated diffusion uses carrier proteins with central channels in the cell membrane.
- Carrier proteins act as selective corridors for molecules like sugars or amino acids.
- The carrier protein binds specifically to a target molecule.
- After binding, the carrier protein changes shape to move the molecule across the membrane.
- Molecules move down their concentration gradient, from high to low concentration.
- The process does not require energy input from the cell (passive transport).
- Facilitated diffusion is similar to simple diffusion but requires a carrier protein.
- The direction of facilitated diffusion depends on the concentration gradient.
- Carrier proteins can move molecules into or out of the cell based on concentration differences.
Key Terms & Definitions
- Facilitated Diffusion — Passive movement of molecules across a membrane with help from carrier proteins.
- Carrier Protein — A membrane protein that binds and transports specific molecules across the cell membrane.
- Concentration Gradient — Difference in concentration of a substance across a space, driving diffusion.
- Passive Transport — Movement of molecules without cell energy expenditure.
Action Items / Next Steps
- Review examples of molecules that use facilitated diffusion (e.g., glucose, amino acids).
- Prepare to compare facilitated diffusion with other membrane transport mechanisms.