Question

When the Na+/K+ pump moves its bound molecules of Na+ to the outside of the membrane, it

A) binds to ATP to release the energy required to power the return trip.

B) pumps more K+ back into the cell than the amount of Na+ that just came out.

C) immediately returns to the inside of the cell, ready to transport more Na+ back outside.

D) releases the bound ATP to return to its normal confirmation.

E) cannot return to the inside empty-handed, so it must bind two K+ first

Answer 1

The Na+/K+ pump must bind two K+ ions before returning to the inside of the cell after exporting three Na+ ions, thus maintaining essential ion gradients and the resting membrane potential of the cell. The correct answer is option E.

Step-by-step explanation:

When the Na+/K+ pump moves its bound molecules of Na+ to the outside of the membrane, it does so in a series of steps using energy from ATP. The process includes the binding of three sodium ions (Na+) to the pump inside the cell, followed by ATP hydrolysis which releases energy and allows the pump to change shape and transport the Na+ ions outside. Subsequently, two potassium ions (K+) from outside the cell bind to the pump.

Finally, the pump returns to its original conformation, releasing the phosphate group and transporting the two K+ ions into the cell.

The correct option that describes what happens when the Na+/K+ pump moves Na+ to the outside of the membrane is E) cannot return to the inside empty-handed, so it must bind two K+ first. This step is crucial because the Na+/K+ pump works to maintain the necessary concentration gradients and electrochemical balance across the cell membrane by pumping out three Na+ ions and bringing in two K+ ions each cycle. This mechanism contributes to the resting membrane potential and is vital for many cellular functions.