Multiple Choice
In the context of Gibbs free energy, how does ATP become ADP during a typical cellular energy-yielding reaction?
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1. Introduction to Biochemistry
Gibbs Free Energy
Multiple Choice
In the context of Gibbs free energy, when is the energy stored in ATP released for cellular work?
A
When ATP is hydrolyzed to ADP and inorganic phosphate (Pi), increasing the amount of products and lowering Gibbs free energy.
B
When ATP binds noncovalently to an enzyme without being hydrolyzed, because binding alone always releases the same amount of free energy as hydrolysis.
C
Only when ATP is converted to cyclic AMP (cAMP), because ATP hydrolysis to ADP is not energetically favorable under cellular conditions.
D
When ATP is synthesized from ADP and Pi, because bond formation directly releases free energy.
Verified step by step guidance1
Understand that Gibbs free energy (\$\(\Delta\) G\$) determines whether a biochemical reaction can perform work spontaneously; a negative \$\(\Delta\) G\$ means the reaction releases free energy.
Recall that ATP stores energy in its high-energy phosphate bonds, and this energy is released when ATP undergoes hydrolysis to form ADP and inorganic phosphate (Pi).
Recognize that the hydrolysis reaction increases the number of product molecules (ADP and Pi) compared to the reactant (ATP), which contributes to a decrease in Gibbs free energy (\$\(\Delta\) G < 0\$).
Note that noncovalent binding of ATP to enzymes without hydrolysis does not release the same amount of free energy as hydrolysis; binding energy alone is usually less and does not involve breaking high-energy bonds.
Understand that ATP synthesis from ADP and Pi requires energy input (it is endergonic), so it does not release free energy; thus, energy stored in ATP is released specifically during ATP hydrolysis to ADP and Pi.
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