All the dehydrogenases of glycolysis and the citric acid cycle use NAD+ (E°' for NAD+/NADH is -0.32 V) as the electron acceptor, except succinate dehydrogenase, which uses covalently bound FAD (E°' for FAD/FADH2 is +0.050 V). Suggest why FAD is a more appropriate electron acceptor than NAD+ in the dehydrogenation of succinate, based on the E°' values of fumarate/succinate (E°' = +0.031 V)

All the dehydrogenases of glycolysis and the citric acid cycle use NAD+ (E°' for NAD+/NADH is -0.32 V) as the electron acceptor, except succinate dehydrogenase, which uses covalently bound FAD (E°' for FAD/FADH2 is +0.050 V). Suggest why FAD is a more appropriate electron acceptor than NAD+ in the dehydrogenation of succinate, based on the E°' values of fumarate/succinate (E°' = +0.031 V)

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter18: Glycolysis

Section: Chapter Questions

Problem 24P: Based on your knowledge of the structure of NAD+ and an assumption that coenzyme dissociation is the...

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All dehydrogenases of glycolysis and the TCA cycle use NAD* (E° for NAD*/NADH is -0.32V) as electron acceptor except succinate dehydrogenase (which uses FAD (E° for FAD/FADH2 is 0.05V). Based on AG° = -NFEº, show and state (1-2 sentences) why is FAD a more appropriate electron acceptor than NAD* in the dehydrogenation of succinate (consider the E° values of %3D Uptake in Na+ Vmax Uptake in absence of Na+ Vmax substrate K: (mM) Kt (mM) L-leucine 420 0.24 23 0.2 D-Leucine 310 4.7 5 4.7 L-valine 225 0.31 19 0.31 fumarate/succinate (E° = 0.031), NAD*/NADH, and the succinate dehydrogenase FAD/FADH2).
All the dehydrogenases of glycolysis and the citric acid cycle use NAD+ (?′°E′° for NAD+/NADH is −0.32 V−0.32 V) as electron acceptor except succinate dehydrogenase, which uses covalently‑bound FAD (?′°E′° for FAD/FADH2 in this enzyme is 0.050 V).0.050 V). The ?′°E′° value for fumarate/succinate is 0.031 V.0.031 V. a)Calculate the Δ?′°Δ⁢G′° value for the oxidation of succinate using NAD+. b)Calculate the Δ?′°Δ⁢G′° value for the oxidation of succinate using covalently‑bound FAD.
The reaction catalyzed by malate dehydrogenase has a ΔG°′ value of +29.7 kJ⋅mol−1. Given what this says about the occurrence of the reaction catalyzed by malate dehydrogenase in cells explain how the reaction catalyzed by citrate synthase (−31.5 kJ⋅mol−1) influences that activity of malate dehydrogenase. In addition, explain how the activity of citrate synthase functions as a regulatory point for the citric acid cycle
The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate by glyceraldehyde 3-phosphate dehydrogenase has an unfavourable equilibrium constant (K'eq= 0.08; G′° = 6.3 kJ/mol), yet the flow at this point in the glycolytic pathway is smooth. How does the cell get out of the unfavourable equilibrium?
Consider one of the reactions of the citric acid cycle shown below Malate + NAD+ ⇆ Oxaloacetate + NADH + H+ (malate dehydrogenase) ΔG˚′ = +29.7 kJ/mol. Describe two factors that allow this thermodynamically unfavorable reaction to occur in the direction of malate to oxaloacetate.
What is unique about how acetyl-CoA carboxylase 1 is regulated compared to any enzyme in glycolysis? Some phospholipid species can be phosphorylated beyond the phosphate attached to the #3 carbon. Describe the likely structure of such a phospholipid. Would the mass / charge (m/z) ratio of this molecular increase or decrease upon modification? Mechanistically, how does NADPH facilitate the removal of an oxygen atom from intermediates in fatty acid synthesis? Will a phosphatidylcholine or a phosphatidylethanolamine have a larger mass / charge (m/z) ratio?
Compare the delta ΔG0' values for the oxidation of succinate by NAD+ and by FAD. Use the data given in Table 18.1 to find the E0' of the NAD+-NADH and fumarate-succinate couples, and assume that E0' for the FAD – FADH2 redox couple is nearly 0.05 V. Why is FAD rather than NAD+ the electron acceptor in the reaction catalyzed by succinate dehydrogenase?
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…
In the citric acid cycle, malate dehydrogenase catalyzes the following reaction: Malate + NAD+ à oxaloacetate + NADH Calculate the standard free energy change for this reaction (∆Go’). Will it proceed as written under standard conditions? What do you think affects the actual free energy change (∆G) allowing for formation of oxaloacetate from malate?
The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate, catalyzed by glyceraldehyde 3- phosphate dehydrogenase, proceeds with an unfavorable equilibrium constant ( K'eq= 0.08; ΔG′° = 6.3 kJ/mol), yet the flow through this point in the glycolytic pathway proceeds smoothly. How does the cell overcome the unfavorable equilibrium?
Some bacteria use the citric acid cycle intermediate, a-ketoglutarate, plus acetyl-CoA, as the starting point for lysine biosynthesis. The first part of this biosynthetic pathway uses the same chemical strategy found in the citric acid cycle. Propose a four-step pathway for the conversion of a-ketoglutarate to 2-oxoadipate. Draw the three missing intermediates, and indicate the chemistry involved in each reaction. Include any cofactors that you think might be required for specific steps.
ATP is an ALLOSTERIC INHIBITOR of the phosphofructokinase enzyme, which is a key catalyst for one of the first steps of Glycolysis. Citrate (citric acid) is a 6-carbon product of the first reaction of the Krebs Cycle (aka Citric Acid Cycle). Interestingly, Citrate enhances the inhibitory effect of ATP on phosphofructokinase. What is a likely explanation for the inhibitory effects of these molecules? Excess ATP and Citrate signal the cell that Glycolysis should be speeded up. Excess ATP and Citrate signal a positive feedback loop. Excess ATP and Citrate signal the cell that Glycolysis should be slowed. Excess ATP and Citrate compete for the active site of phosphofructokinase.