Multiple Choice
In the context of Gibbs free energy and energy coupling in cells, the reaction ATP ADP ATP is best described as which of the following?
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1. Introduction to Biochemistry
Gibbs Free Energy
Multiple Choice
In the context of Gibbs free energy, what happens when a terminal phosphate group is removed from ATP by hydrolysis?
A
ATP remains unchanged because breaking the phosphate bond requires exactly as much energy as is released, so .
B
ATP is converted to ADP and inorganic phosphate, and free energy is released (the reaction has under typical cellular conditions).
C
ATP is converted to ADP only (no inorganic phosphate is produced), and the reaction is strongly endergonic.
D
ATP is converted to AMP and pyrophosphate, and free energy is absorbed (the reaction has under typical cellular conditions).
Verified step by step guidance1
Understand that ATP hydrolysis involves breaking the bond between the terminal phosphate group and the rest of the molecule, resulting in the formation of ADP (adenosine diphosphate) and inorganic phosphate (Pi).
Recall that Gibbs free energy change (\$\(\Delta\) G\$) indicates whether a reaction releases or requires energy: \$\(\Delta\) G < 0\$ means the reaction is exergonic (releases energy), and \$\(\Delta\) G > 0\$ means it is endergonic (requires energy).
Recognize that under typical cellular conditions, ATP hydrolysis is exergonic, meaning it releases free energy, so \$\(\Delta\) G < 0\$ for this reaction.
Note that the reaction can be summarized as: \$\(\mathrm{ATP}\) + \(\mathrm{H_2O}\) \(\rightarrow\) \(\mathrm{ADP}\) + \(\mathrm{Pi}\) + \(\text{free energy}\)\$, where the free energy released is used to drive many cellular processes.
Conclude that the removal of the terminal phosphate group from ATP by hydrolysis converts ATP to ADP and inorganic phosphate, releasing free energy, which is why the reaction has a negative Gibbs free energy change (\$\(\Delta\) G < 0\$).
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