Final answer:
The plasma-membrane Na+/K+ ATPase is the main ATP-powered pump that maintains ion gradients in mammalian cell membranes.
Step-by-step explanation:
The major ATP-powered pump responsible for maintaining ion gradients across the plasma membrane of mammalian cells is the plasma-membrane Na+/K+ ATPase. This pump is instrumental in maintaining the necessary electrochemical gradient within the cell.
how this pump functions includes several steps. Firstly, ATP is hydrolyzed, attaching a phosphate to the pump and causing an allosteric change in shape. This new conformation allows the pump to bind and release three Na+ ions outside the cell. Subsequently, two K+ ions from the extracellular fluid bind to the pump. This binding leads to the removal of the phosphate and restores the pump's original shape, releasing the K+ ions into the cytoplasm. The Na+/K+ pump is then ready for another cycle. Thus, this ATPase pump is crucial for active transport, moving ions against their concentration gradients with the help of energy from ATP.
The sodium-potassium pump moves Na⁺ out of the cell and K⁺ into the cell, using the energy from ATP. It does this by changing its conformation when ATP is hydrolyzed and binding and releasing sodium and potassium ions to their respective sides of the membrane. This process allows for the maintenance of the correct concentrations of sodium and potassium ions in the cell.
For example, in a single cycle of the pump, three sodium ions are extruded from the cell, while two potassium ions are imported into the cell.