Turning one cycle of the sodium-potassium pump, exporting three sodium ions and importing two potassium ions, costs:
ANo ATP molecules at all
BHalf an ATP molecule
CTwo ATP molecules exactly
DOne ATP molecule exactly
Answer & Solution
Correct answer: D. One ATP molecule exactly
1. The pump moves both ions against their gradients, so it cannot run for free.
2. It is powered by energy coupling to ATP hydrolysis.
3. In order for the pump to turn one cycle, exporting three sodium ions and importing two potassium ions, one molecule of ATP must be hydrolyzed.
4. A large percentage of a cell's ATP is spent powering this pump.
5. The phosphate released binds the pump, a process called phosphorylation.
_Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 6 'Metabolism', sections 6.1-6.5_
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