Overview
This lecture explains how carrier proteins work in cell membranes, highlighting their roles in both facilitated diffusion and active transport.
Carrier Proteins and Their Function
- Carrier proteins span the cell membrane and help transport substances across it.
- These proteins can assist in both active transport and facilitated diffusion.
- A carrier protein changes shape (conformation) when a specific molecule binds to it.
- The conformational change shifts the opening of the carrier from one side of the membrane to the other.
- The transported molecule detaches inside the cell, and the carrier returns to its original shape, ready to repeat the process.
- Shape changes in carrier proteins are central to their function in transporting molecules.
Facilitated Diffusion vs. Active Transport
- Facilitated diffusion uses carrier proteins to move molecules down their concentration gradient (high to low) without energy input.
- Active transport moves molecules against their concentration gradient (low to high), requiring energy, usually from ATP.
- Identifying the type: moving substances with the gradient = facilitated diffusion; against the gradient = active transport.
- Example: Moving a molecule from extracellular fluid (low concentration) to intracellular fluid (high concentration) is active transport.
Key Terms & Definitions
- Carrier Protein — A membrane protein that binds and transports specific substances across the cell membrane.
- Conformational Change — A change in the shape of a protein, often triggered by molecule binding.
- Facilitated Diffusion — Passive transport of substances across a membrane with the help of carrier proteins, down their concentration gradient.
- Active Transport — Movement of substances across a membrane against their concentration gradient, requiring energy.
Action Items / Next Steps
- Review examples of facilitated diffusion and active transport in your textbook.
- Prepare to discuss specific carrier protein mechanisms in the next class.