Question

Provide a definition of primary active transport and describe how it works in the case of the Na/K ATPase

Answer 1

Ans.

• Primary active transport is a type of active transport where ATP is used as an energy source for transportation of molecules across the membrane against their concentration gradient.
• Molecules which are capable of primary active transport include ion pumps.
• Na/K ATPase, also known as sodium-potassium or Na/K - pump, is an enzyme and one of the most important ion pumps found in animal cells, which uses primary active transport.
• This pump causes movement of sodium ions out of cells whereas potassium ion is moved inside the cells in a repeating cycle.
• In every repeat of cycle, 3 sodium ions are moved out of the cell whereas 2 potassium ions are moved inside the cell.
• The Na/K ATPase primarily functions by maintaining a high potassium concentration inside the cell, thus making the concentration gradient of potassium very steep.
• Steps of the Na/K ATPase mechanism are as follows;

1. Opening of pump inside the cell takes place in the begining and binds 3 sodium ions.
2. Binding of sodium ion causes hydrolysis of ATP. From ATP, a phosphte group is associated to the pump, which is then phosphorylated and releases ADP as a by-product.
3. Because of the phosphorylation, the pump undergoes a change in shape and re-orient itself, thus opening in the direction of extracellular space. This conformation results in the release of 3 sodium ions out of cell.
4. While facing outside, the pump binds to two potassium ions and this results in the removal of phosphate groups attached to the pump.
5. With the removal of phosphate group, the pump returns back to it's initial conformation and opens inside the cell.
6. During it's inward conformation, the pump releases 2 potassium ions into the cytoplasm.

• By releasing the potassium ions, the pump returns back to it's normal state, where it was during step 1 and the cycle re-starts.
• This pump plays important role in several essential physiological processes such as maintenance of resting potential and regulation of cellular volume.