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Why can active transport move sodium ions out of a cell against a concentration gradient?
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Artist's conception of a human neuron.
Active transport moves sodium ions out of a cell against a concentration gradient by coupling the transport process to the hydrolysis of adenosine triphosphate (ATP), which provides the necessary metabolic energy.12
This process is facilitated by a specialized intrinsic protein in the cell membrane known as the sodium-potassium pump, or sodium-potassium-activated ATPase. The mechanism functions as follows:1
- Energy Coupling: The pump uses energy from splitting ATP to force sodium ions out of the cell, where their concentration is already high, and move potassium ions into the cell.13
- Conformational Changes: The enzyme exists in two major conformations. Sodium ions catalyze the transfer of a phosphate group from ATP to the enzyme, which triggers the release of sodium outside the cell.1
- Cycle Completion: Potassium ions subsequently catalyze the release of the phosphate from the enzyme, allowing the protein to return to its original state and repeat the cycle.1
By transferring free energy from the pump to the ions, the cell maintains essential concentration gradients required for proper cellular function.13