Overview
The lecture covers active transport, distinguishing it from passive transport, exploring primary and secondary active transport, and providing key examples such as the sodium-potassium pump and sodium-glucose symporters.
Passive vs. Active Transport
- Passive transport moves substances from high to low concentration without energy input (simple and facilitated diffusion).
- Active transport moves substances from low to high concentration, requiring energy input.
Types of Active Transport
- Primary active transport uses direct ATP investment to move substances against their gradients.
- Secondary active transport uses the energy from an existing gradient (created by primary transport) to move other substances.
Types of Transporters
- Uniport: Moves a single molecule through a transporter.
- Symport: Moves two different molecules in the same direction through a transporter.
- Antiport: Moves two different molecules in opposite directions through a transporter.
Primary Active Transport Example: Sodium-Potassium Pump (Na⁺/K⁺ ATPase)
- Moves 3 sodium ions out and 2 potassium ions into the cell, both against their gradients, using ATP.
- The unequal movement of charges makes the pump electrogenic, contributing to the negative resting membrane potential.
- Essential for maintaining cell volume and sodium/potassium balance—crucial in nerve cells.
- Failure of this pump (e.g., during a heart attack) can cause cell swelling and death due to sodium and water buildup inside the cell.
Secondary Active Transport Example: Sodium-Glucose Linked Transporter (SGLT)
- SGLT uses symport to bring sodium (down its gradient) and glucose (against its gradient) into the cell.
- The sodium gradient, generated by the sodium-potassium pump, powers glucose uptake—hence "secondary" active transport.
- Found in intestinal epithelial cells for glucose absorption.
- If the sodium-potassium pump fails, secondary transport will also stop.
Other Secondary Active Transporters
- Sodium-calcium exchanger (antiport): Sodium in, calcium out.
- Sodium-hydrogen exchanger (antiport): Sodium in, hydrogen out.
Key Terms & Definitions
- Passive Transport — movement from high to low concentration, no energy required.
- Active Transport — movement from low to high concentration, requires energy.
- Primary Active Transport — direct ATP investment to move molecules.
- Secondary Active Transport — uses gradients formed by primary active transport for energy.
- Uniport — transporter moving a single type of molecule.
- Symport — transporter moving two molecules in the same direction.
- Antiport — transporter moving two molecules in opposite directions.
- Electrogenic — transport that creates an electrical difference across the membrane.
Action Items / Next Steps
- Review the mechanisms and functions of Na⁺/K⁺ ATPase and SGLT.
- Prepare for upcoming coverage on osmosis and its relationship to active transport.