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?

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?

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter25: Nitrogen Acquisition And Amino Acid Metabolism

Section: Chapter Questions

Problem 22P

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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.
The malaria parasite Plasmodium falciparum does not carry out oxidative phosphorylation and therefore does not use the citric acid cycle to generate reduced cofactors. Instead, the parasite converts amino acid–derived α ketoglutarate to succinate. Write an equation for the α-ketoglutarate → succinate conversion that follows (a) the oxidative (clockwise) path of the citric acid cycle or (b) the reductive (counterclockwise) path of the cycle.
Consider the malate dehydrogenase reaction from the citric acid cycle. Given the listed concentrations, calculate the free energy change for this reaction at energy change for this reaction at 37.0 °C (310 K). AG' for the reaction is +29.7 kJ/mol. Assume that the reaction occurs at pH 7. [malate] 1.25 mM [oxaloacetate] = 0.290 mM [NAD+] = 430 mM [NADH] : = 170 mM AG : kJ-mol-1 * TOOLS x10
Consider the malate dehydrogenase reaction from the citric acid cycle. Given the listed concentrations, calculate the free energy change for this reaction at energy change for this reaction at 37.0 °C (310 K). AG' for the reaction is +29.7 kJ/mol. Assume that the reaction occurs at pH 7. [malate] = 1.43 mM [oxaloacetate] = 0.220 mM [NAD*] = 460 mM [NADH] = 180 mM AG : kJ-mol-1
Consider the malate dehydrogenase reaction from the citric acid cycle. Given the listed concentrations, calculate the free energy change for this reaction at energy change for this reaction at 37.0 ˚C (310 K). AG' for the reaction is +29.7 kJ/mol. Assume that the reaction occurs at pH 7. [malate] = 1.45 mM AG: [oxaloacetate] = 0.130 mM [NAD+ ] = 110 mM [NADH] = 44 mM 47.06 Incorrect kJ.mol-1
Given the following information, calculate the physiological ΔG of the isocitrate dehydrogenase reaction at 25°C and pH 7.0: [NAD+]/[NADH] = 8, [α-ketoglutarate] = 0.1 mM, and [isocitrate] = 0.02 mM. Assume standard conditions for CO2 (ΔG°′ is given in Table). Is this reaction a likely site for metabolic control?
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
Certain microorganisms with an incomplete citric acid cycle decarboxylate α-ketoglutarate to produce succinate semialdehyde. A dehydrogenase then converts succinate semialdehyde to succinate. These reactions can be combined with other standard citric acid cycle reactions to create a pathway from citrate to oxaloacetate. Compare the ATP and reduced cofactor yield of the standard and alternate pathways.
In the citric acid cycle, the coenzyme NAD is required for which of the following reactions (Choose all that apply) O hydration of fumarate to malate O isomerization of citrate to isocitrate O oxidation of succinate to fumarate. O oxidation of isocitrate to the oxalosuccinate intermediate to permit beta decarboxylation of isocitrate to alpha-ketoglutarate condensation of acetyl-CoA and oxaloacetate to form citrate oxidation of malate to oxaloacetate decarboxylation of alpha-ketoglutarte to succinyl CoA O conversion of succinyl-CoA to succinate
(a) Consider the oxidation of malate to oxaloacetate by NAD*: malate + NAD+ → oxaloacetate + NADH + H+ In yeast mitochondria, where the pH = 8.1, this reaction is exergonic only at low oxaloacetate concentrations. Assuming a pH = 8.1, a temperature of 37 °C, and the steady-state concentrations given below, calculate the maximum concentration of oxaloacetate at which the reaction will still be exergonic. malate + NAD*→ oxaloacetate + NADH + H* lactate + NAD →→ pyruvate + NADH + H+ half reaction Pyruvate + 2H+ + 2e → lactate Pyruvate + CO₂ + H + 2e → malate Intracellular steady state concentrations: malate = 410 μM; NAD = 20.0 mM; pyruvate = 3.22 mM; NADH = 290 μM; AG=+29.7 kJ/mol AG¹ = +25.1 kJ/mol E° (V) - 0.190 - 0.330 lactate 1.1 mM CO₂ = 15.5 torr
The half-reactions involved in the lactate dehydrogenase (LDH) reaction and their standard reduction potentials are (see attached)). Calculate ΔG at pH 7.0 for the LDH-catalyzed reduction of pyruvate under the following conditions: (a) [lactate]/[pyruvate] = 1 and [NAD+]/[NADH] = 1. (b) [lactate]/[pyruvate] = 160 and [NAD+]/[NADH] = 160. (c) [lactate]/[pyruvate] = 1000 and [NAD+]/[NADH] = 1000. (d) Discuss the eff ect of the concentration ratios in Parts a–c on the direction of the reaction.
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?