Overview
This lecture explains the three main types of carrier proteins—uniporters, symporters, and antiporters—and how they transport solutes across cell membranes.
Carrier Proteins and Membrane Transport
- Carrier proteins bind solute molecules and change shape to transport them across membranes.
- Transport can be selective, enabling the movement of specific solutes only.
Uniporters
- Uniporters carry a single type of solute across the membrane.
- Selectively bind to their specific solute (e.g., only hexagons) and move it to the other side.
Symporters
- Symporters transport two different solutes in the same direction across the membrane.
- One solute moves down its concentration gradient, providing the energy to move the second solute against its gradient.
- Example: green circles move down their gradient, powering purple hexagons against theirs.
Antiporters
- Antiporters move two different solutes in opposite directions across the membrane.
- Both solutes can be transported against their concentration gradients, which requires an input of energy (e.g., ATP hydrolysis).
- Example: green circles move out while brown triangles move in, both against their gradients.
Summary of Carrier Types
- Uniporter: transports one solute type.
- Symporter: moves two solutes together in the same direction.
- Antiporter: exchanges two solutes in opposite directions.
Key Terms & Definitions
- Carrier protein — A membrane protein that binds and transports specific solute molecules across the membrane.
- Uniporter — Carrier protein that transports only one type of solute.
- Symporter — Carrier protein that co-transports two solutes in the same direction.
- Antiporter — Carrier protein that transports two solutes in opposite directions.
- Concentration gradient — Difference in solute concentration across a membrane.
- Active transport — Movement of solutes against their concentration gradients, requiring energy input (e.g., ATP hydrolysis).
Action Items / Next Steps
- Review examples of each carrier protein type in your textbook.
- Practice drawing diagrams of uniporters, symporters, and antiporters.