Question

you know that the outside of the plasma membrane is more positive than the inside. describe how this charge differential is formed by the Na+/K+ pump.

Answer 1

sodium–potassium pump is found in many cell (plasma) membranes.

Powered by ATP, the pump moves sodium and potassium ions in opposite directions, each against its concentration gradient. In a single cycle of the pump, three sodium ions are extruded from cell and two potassium ions are imported into the cell.

The pump, after binding ATP, binds 3 intracellular Na+  ions.

ATP is hydrolyzed, leading to phosphorylation of the pump at a highly conserved aspartate residue and subsequent release of ADP.

A conformational change in the pump exposes the Na+

ions to the outside. The phosphorylated form of the pump has a low affinity for Na+  ions, so they are released.

The pump binds 2 extracellular K+ions. This causes the dephosphorylation of the pump, reverting it to its previous conformational state, transporting the K+ ions into the cell.

The unphosphorylated form of the pump has a higher affinity for Na+ ions than K+ions, so the two bound K+ ions are released. ATP binds, and the process starts again.

Hence Na k pump moves 3 Na ions out of cell and moves 2 potassium inside cell. There is net loss of one positive ion inside cell. Which creates positive charge outside cell.