Via A Protein Channel [new] | Active Transport

Imagine a tiny, bustling cell as a large office building. This building is surrounded by a thick, brick wall (the cell membrane ), which keeps everything secure. Outside the wall, there’s a chaotic street filled with sodium ions (Na⁺) — think of them as urgent, first-class letters .

A molecule of ATP comes along and donates a phosphate group (a tiny energy packet) to the pump. This energy changes the shape of the protein channel.

The pump is now in its “open to the outside” shape. It loves potassium ions (K⁺). It grabs two potassium ions from outside.

Because the pump changed shape, it now swings open to the outside of the wall. The three sodium ions, no longer able to hang on, tumble out into the crowded street. They have moved from low concentration (inside) to high concentration (outside). That is active transport .