Question

Why is the sodium-potassium pump an example of active transport?

Answer 1

Active transport is the process of transport of a substance from a lower concentration to a higher concentration by the use of energy (ATP) against the concentration gradient. This process is also known as the uphill transport mechanism. Sodium- potassium pump utilizes energy for the movement of sodium and potassium ions against the concentration gradient. Three sodium ions are exchanged with two potassium ions.

Complete answer:
The sodium-potassium pump has a binding site for three sodium ions and two potassium ions and a site for ATP binding. Initially, in resting condition, no sodium and potassium are attached to the pump. When three sodium ions bind to the pump, an ATP molecule binds to the protein and releases the phosphate ion and conformational change of the protein molecule occurs which results in the release of the sodium ions into the other side of the cell membrane. After the pump is free from all the sodium ions, this now has a high affinity for the potassium molecule. The potassium molecule from the other side of the cell membrane binds to the binding sites of the potassium and is transported to the other side of the cell membrane and at the same time, the phosphate ion is released from the carrier protein molecule. Hence it can be called an active transport mechanism.

Note:
It is to be kept in mind that the concentration of sodium ions outside the cell is lower and that of the potassium ion inside the cell is lower. The movement of sodium ions is from inside of the cell to the outside of the cell membrane (efflux) against the concentration gradient and the movement of the potassium ion is from outside to the inside of the cell (influx) against the concentration gradient.