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Why is a large negative free energy change a good candidate for a controlling step in a metabolic pathway while a step in a metabolic pathway with a AG 2 0 is NOT? Be sure to explain your answer.

Why is a large negative free energy change a good candidate for a controlling step in a metabolic pathway while a step in a metabolic pathway with a AG 2 0 is NOT? Be sure to explain your answer.

Biochemistry
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
Problem 1P
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### Question: Why is a large negative free energy change a good candidate for a controlling step in a metabolic pathway while a step in a metabolic pathway with a ΔG ≈ 0 is NOT? Be sure to explain your answer. ### Explanation: In metabolic pathways, steps with a large negative free energy change (ΔG) often serve as control points because they are essentially irreversible under physiological conditions. This irreversibility means that once the pathway reaches this step, the reaction is committed to proceed in a specific direction. Therefore, these steps can be tightly regulated, ensuring that metabolic flow is responsive to cellular demands and environmental conditions. On the other hand, steps with a ΔG ≈ 0 are near equilibrium and reversible. They do not significantly impact the overall directionality of the pathway because small changes in substrate or product concentrations can easily reverse the reaction. Therefore, these steps are not effective control points, as they don’t commit the flow of metabolites in the same manner. Control of flux through these reactions is weak, so they are less often the targets of regulation.
Transcribed Image Text:### Question: Why is a large negative free energy change a good candidate for a controlling step in a metabolic pathway while a step in a metabolic pathway with a ΔG ≈ 0 is NOT? Be sure to explain your answer. ### Explanation: In metabolic pathways, steps with a large negative free energy change (ΔG) often serve as control points because they are essentially irreversible under physiological conditions. This irreversibility means that once the pathway reaches this step, the reaction is committed to proceed in a specific direction. Therefore, these steps can be tightly regulated, ensuring that metabolic flow is responsive to cellular demands and environmental conditions. On the other hand, steps with a ΔG ≈ 0 are near equilibrium and reversible. They do not significantly impact the overall directionality of the pathway because small changes in substrate or product concentrations can easily reverse the reaction. Therefore, these steps are not effective control points, as they don’t commit the flow of metabolites in the same manner. Control of flux through these reactions is weak, so they are less often the targets of regulation.
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