Sodium-Potassium pumps
The cell membrane as an electrical
battery

Active transport is responsible for cells
containing relatively high concentrations
of potassium ions but low concentrations
of sodium ions. Requires E (ATP)

The mechanism responsible for this is the
sodium-potassium pump which moves
these two ions in opposite directions
across the plasma membrane.
Concentrations of sodium and potassium ions on the
two other sides of the membrane are interdependent,
suggesting that the same carrier protein transports both
ions. (green channel protein, red ATP-ase)
The carrier is an ATP-ase and it pumps 3 sodium ions out of
the cell for every 2 potassium ions pumped in.
Function of the pump
The Na+/K+-ATPase helps maintain
resting potential, assists transport
and regulates cellular volume.
 In order to maintain the cell’s resting
potential, cells must keep a low
concentration of ↓ sodium ions &
high levels of ↑ potassium ions
within the cell.

Potential? Means E possibility

Potential: a gradient where there are
different concentrations of ions on
either side of a membrane just like a
battery with + and – sides

When the cell is at rest there is a
homeostatic state called the resting
potential & cell has good volume

Cells need to bring in substances
(glucose, amino acids) by facilitated
transport

The battery is maintained using ATP
continuously to force sodium out of
the cell & potassium into the cell.

3 Na+ out for every 2 K+ in

Movement of sodium from one side
of a cell membrane to the other side
creates an osmotic gradient that
drives the absorption of water.

Water diffuses back into the cell
carrying needed substances =
facilitated transport
Concentrations of sodium and potassium ions on the
two other sides of the membrane are interdependent,
suggesting that the same carrier protein transports both
ions. (green channel protein, red ATP-ase)
The carrier is an ATP-ase and it pumps 3 sodium ions out of
the cell for every 2 potassium ions pumped in.