Here's how it works:
1. Binding of Sodium Ions: Three sodium ions (Na+) bind to the pump protein on the intracellular side.
2. Phosphorylation: ATP is hydrolyzed (broken down) into ADP (adenosine diphosphate) and a phosphate group. This phosphate group attaches to the pump protein, changing its shape and increasing its affinity for potassium ions.
3. Sodium Transport: The shape change causes the pump to release the three sodium ions outside the cell.
4. Binding of Potassium Ions: Two potassium ions (K+) bind to the pump protein on the extracellular side.
5. Dephosphorylation: The phosphate group detaches from the pump protein, causing it to return to its original shape.
6. Potassium Transport: The shape change releases the two potassium ions into the cell.
This cycle continues, using the energy from ATP hydrolysis to move sodium ions out of the cell and potassium ions into the cell against their concentration gradients.
Therefore, the sodium-potassium pump is an active transport system that requires energy to function.
