ATP is the “energy currency” of cells. Potential energy is stored in the P~O bonds of ATP. Some of the free energy released by exergonic reactions can be captured in the form of ATP. This energy can then be released by ATP hydrolysis and used to drive endergonic reactions.
learning outcomes
You should be able to:
Explain the characteristics of ATP that account for the high free energy released during its hydrolysis to form ADP and Pi.
Analyze evidence to identify reactions as exergonic or endergonic.
Predict biochemical transformations that require coupling to ATP hydrolysis.
What chemical properties allow ATP to store energy?
ATP has terminal phosphate groups that repel one another, so it takes energy to form a bond between them. Some of this energy is stored as potential energy. Also, hydrolysis of phosphate releases energy because the free energy of the P~O bond is higher than the free energy of the OH bond formed by hydrolysis.
The following is a biochemical reaction that involves ATP:
Phosphoenolpyruvate → pyruvate (ΔG = +10 kcal/mol)
Is the reaction exergonic or endergonic?
The reaction is endergonic (positive ΔG).
Is ATP hydrolyzed or formed during the reaction?
ATP hydrolysis can drive the reaction (ΔG = -7.3kcal/mol).
ATP is synthesized and used up very rapidly. But these biochemical reactions—