In active transport, energy is used to move a solute against its concentration gradient.For each molecule of ATP used, 2 K+ are pumped into the cell and 3 Na+ are pumpedout of the cell.

Outside of cell

Inside of cell

Na+

K+

Sodium–potassium

pump

Figure 5.13 Primary Active Transport: The Sodium–Potassium Pump

1. 3 Na+ and 1 ATP bind to the protein “pump.”

Extracellular space

Cytoplasm

K+

ATP

Na+

Figure 5.13 Primary Active Transport: The Sodium-Potassium Pump

2. ADP is released, causing a change in the pump’s shape.

Extracellular space

Cytoplasm

K+

ADP

Pi

Figure 5.13 Primary Active Transport: The Sodium-Potassium Pump

3. 3 Na+ are released as 2 K+ bind to the pump.

Extracellular space

CytoplasmPi

Figure 5.13 Primary Active Transport: The Sodium-Potassium Pump

4. Pi is released, causing the pump’s shape to change, and releasing 2 K+

Extracellular space

Cytoplasm

Pi K+

Figure 5.13 Primary Active Transport: The Sodium-Potassium Pump