The glucose/glucose-6-phosphate substrate cycle involves distinct reactions of glycolysis and gluconcogenesis that interconvert these two metabolites. Assume that under physiological conditions, [ATP] = [ADP] and [Pi] =1 mM. Consider the following glycolytic reaction catalyzed by hexokinase: ATP + glucose = AG' = -16.7 kJ/mol ADP + glucose-6-phosphate (a) Calculate the equilibrium constant (K) for this reaction at 298 K, and from that, calculate the maximum [glucose-6-phosphate]/[glucose] ratio that would exist under conditions where the reaction is still thermody- namically favorable. (b) The reverse of this interconversion in gluconeogenesis is catalyzed by glucose-6-phosphatase: glucose-6-phosphate + H,0 = glucose + P, AGr = -13.8 kJ/mol K= 262 for this reaction. Calculate the maximum ratio of [glucose]/ [glucose-6-phosphate] that would exist under conditions where the reaction is still thermodynamically favorable. (c) Under what cellular conditions would both directions in the substrate cycle be strongly favored? (d) What ultimately controls the direction of net conversion of a substrate cycle such as this in the cell?
The glucose/glucose-6-phosphate substrate cycle involves distinct reactions of glycolysis and gluconcogenesis that interconvert these two metabolites. Assume that under physiological conditions, [ATP] = [ADP] and [Pi] =1 mM. Consider the following glycolytic reaction catalyzed by hexokinase: ATP + glucose = AG' = -16.7 kJ/mol ADP + glucose-6-phosphate (a) Calculate the equilibrium constant (K) for this reaction at 298 K, and from that, calculate the maximum [glucose-6-phosphate]/[glucose] ratio that would exist under conditions where the reaction is still thermody- namically favorable. (b) The reverse of this interconversion in gluconeogenesis is catalyzed by glucose-6-phosphatase: glucose-6-phosphate + H,0 = glucose + P, AGr = -13.8 kJ/mol K= 262 for this reaction. Calculate the maximum ratio of [glucose]/ [glucose-6-phosphate] that would exist under conditions where the reaction is still thermodynamically favorable. (c) Under what cellular conditions would both directions in the substrate cycle be strongly favored? (d) What ultimately controls the direction of net conversion of a substrate cycle such as this in the cell?
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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![The glucose/glucose-6-phosphate substrate cycle involves distinct reactions
of glycolysis and gluconcogenesis that interconvert these two metabolites.
Assume that under physiological conditions, [ATP] = [ADP] and
[Pi] =1 mM.
Consider the following glycolytic reaction catalyzed by hexokinase:
ATP + glucose = AG' = -16.7 kJ/mol
ADP + glucose-6-phosphate
(a) Calculate the equilibrium constant (K) for this reaction at 298 K, and
from that, calculate the maximum [glucose-6-phosphate]/[glucose] ratio
that would exist under conditions where the reaction is still thermody-
namically favorable.
(b) The reverse of this interconversion in gluconeogenesis is catalyzed by
glucose-6-phosphatase:
glucose-6-phosphate + H,0 =
glucose + P, AGr = -13.8 kJ/mol
K= 262 for this reaction. Calculate the maximum ratio of [glucose]/
[glucose-6-phosphate] that would exist under conditions where the
reaction is still thermodynamically favorable.
(c) Under what cellular conditions would both directions in the substrate
cycle be strongly favored?
(d) What ultimately controls the direction of net conversion of a substrate
cycle such as this in the cell?](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Ffe220f9b-e0f0-46f2-8683-3cfa002b7054%2F07ddcc58-d024-4b82-b9fa-e67ed88c08f1%2Fwnpzu7_processed.png&w=3840&q=75)
Transcribed Image Text:The glucose/glucose-6-phosphate substrate cycle involves distinct reactions
of glycolysis and gluconcogenesis that interconvert these two metabolites.
Assume that under physiological conditions, [ATP] = [ADP] and
[Pi] =1 mM.
Consider the following glycolytic reaction catalyzed by hexokinase:
ATP + glucose = AG' = -16.7 kJ/mol
ADP + glucose-6-phosphate
(a) Calculate the equilibrium constant (K) for this reaction at 298 K, and
from that, calculate the maximum [glucose-6-phosphate]/[glucose] ratio
that would exist under conditions where the reaction is still thermody-
namically favorable.
(b) The reverse of this interconversion in gluconeogenesis is catalyzed by
glucose-6-phosphatase:
glucose-6-phosphate + H,0 =
glucose + P, AGr = -13.8 kJ/mol
K= 262 for this reaction. Calculate the maximum ratio of [glucose]/
[glucose-6-phosphate] that would exist under conditions where the
reaction is still thermodynamically favorable.
(c) Under what cellular conditions would both directions in the substrate
cycle be strongly favored?
(d) What ultimately controls the direction of net conversion of a substrate
cycle such as this in the cell?
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