The \u0394G of ATP hydrolysis in a test tube under standard conditions is -7.3 kcal/mol. The \u0394G for the reaction A+B \u2192 C under the same conditions is +4.0 kcal/mol. How would the addition of an enzyme that catalyzes A+B \u2192 C most likely alter the coupled reactions?
A. It would increase the rate of production of C and increase the overall \u0394G for the coupled reactions
B. It would result in no change in the rate of production of C and decrease the overall \u0394G for the coupled reactions
C. It would increase the rate of production of C and decrease the overall \u0394G for the coupled reactions
D. It would result in no change in the overall \u0394G for the coupled reactions
Answer (2)
The addition of an enzyme that catalyzes the reaction A + B → C will increase the rate of production of C, but it will not alter the overall Δ G for the coupled reactions. Therefore, the correct choice is D: It would result in no change in the overall Δ G for the coupled reactions.
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ATP hydrolysis releases energy ( Δ G = -7.3 kcal/mol), while the reaction A + B -> C requires energy ( Δ G = +4.0 kcal/mol).
The overall Δ G for the coupled reactions is -3.3 kcal/mol.
An enzyme increases the rate of the reaction A + B -> C but does not change the overall Δ G .
Therefore, the enzyme increases the rate of production of C and does not change the overall Δ G for the coupled reactions.
Explanation
Understanding the Reactions The problem describes two coupled reactions: ATP hydrolysis (which releases energy) and the reaction A + B -> C (which requires energy). We're asked how an enzyme that catalyzes the second reaction will affect the overall process.
Gibbs Free Energy The Gibbs free energy ( Δ G ) of ATP hydrolysis is -7.3 kcal/mol, meaning it releases 7.3 kcal of energy per mole of ATP. The Δ G for the reaction A + B -> C is +4.0 kcal/mol, meaning it requires 4.0 kcal of energy per mole of C produced.
Overall Gibbs Free Energy When these reactions are coupled, the energy released by ATP hydrolysis can drive the reaction A + B -> C. The overall Δ G for the coupled reactions is the sum of the individual Δ G values:
Δ G overall = Δ G ATP + Δ G reaction = − 7.3 kcal/mol + 4.0 kcal/mol = − 3.3 kcal/mol
This means the overall coupled reaction is spontaneous (releases energy).
Role of Enzymes Enzymes are catalysts, meaning they speed up reactions by lowering the activation energy. They do not change the overall Gibbs free energy ( Δ G ) of a reaction. Therefore, the enzyme will increase the rate of production of C, but it will not change the overall Δ G of the coupled reactions.
Conclusion Therefore, the addition of the enzyme will increase the rate of production of C and will not change the overall Δ G for the coupled reactions.
Examples
Enzymes are like matchmakers in the cell! Imagine you're trying to build a house (reaction A + B -> C), but it takes a lot of effort to get started. ATP hydrolysis is like a power source that provides the initial energy. An enzyme is like a skilled builder who makes the process faster and more efficient, but doesn't change the overall energy needed to complete the house. This principle applies to many biological processes, from digesting food to building proteins.
