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?

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?

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter23: Fatty Acid Catabolism

Section: Chapter Questions

Problem 21P: Using the ActiveModel for enoyl-CoA dehydratase, give an example of a case in which conserved...

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Ethanol as a Source of Metabolic Energy (Integrates with Chapters 19 and 20.) Acetate produced in ethanol metabolism can be transformed into acetyl-COA by the acetyl thiokinase reaction: Acetate+ATP+CoASHacetyleCoA+AMP+PPiAcetyle-CoA then can enter the citric acid cycle and undergo oxidation to 2 CO2by this route, assuming oxidative phosphorylation is part of the process? (Assume all reactions prior to acetyl-CoA entering the citric acid cycle occur outside the mitochondrion). Per carbon atom, which is a better metabolic fuel, ethanol or glucose? That is, how many ATP equivalents per carbon atom are generated by combustion of glucose versus ethanol to CO2?
Using the ActiveModel for enoyl-CoA dehydratase, give an example of a case in which conserved residues in slightly different positions can change the catalytic rate of 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?
Although most enzymes are quite specific, they can catalyze side reactions with compounds that are structurally similar to their physiological substrates, but usually at much slower rates. For example, glyceraldehyde- 3-phosphate dehydrogenase (GAPDH), which normally catalyzes the oxidative phosphorylation of glyceraldehyde-3-phosphate, can slowly convert erythrose-4-phosphate, an intermediate in the pentose phosphate pathway, to 1,4-bisphosphoerythronate: Draw a plausible mechanism for this side reaction of GAPDH.
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
A mutated IDH1 isoenzyme is found in a high percentage of a type of brain cancer called glioblastoma. Instead of converting isocitrate to α-ketoglutarate, mutated IDH1 converts its substrate to 2-hydroxyglutarate, a circumstance that disrupts the citric acid cycle, among other effects. Review the structures of isocitrate and α-ketoglutarate and determine the structure of 2- hydroxyglutarate
Phosphoglycerate mutase (PGM) catalyzes the interconversion of 3-phosphoglycerate (3PG) and 2-phosphoglycerate (2PG) in the glycolytic and gluconeogenic pathways. a) To what enzyme class does PGM belong? b) There are two distinct classes of PGM, one which is dependent on 2,3-bisphosphoglycerate (2,3-BPG), dPGM, and one which is not, iPGM. dPGM uses acid base chemistry and a phosphorylated histidine residue to interconvert 3PG and 2PG. The dPGM reaction proceeds with formation of 2,3-BPG as an intermediate. Propose a mechanism for the dPGM-catalyzed conversion of 3PG to 2PG that is consistent with this information. c) What is the purpose of 2,3-BPG (i.e., why does dPGM require it)?
Refer to Figure, which indicates ∆G for each glycolytic reaction under intracellular conditions. Assume that glyceraldehyde-3-phosphate dehydrogenase was inhibited with iodoacetate, which reacts with its active site cysteine sulfhydryl group. Which glycolytic intermediate would you expect to accumulate most rapidly, and why?
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.
The conversion of 1 mol of fructose 1,6-bisphosphate to 2 mol of pyruvate by the glycolytic pathway results in what type of net formation?
Because dichloroacetate inhibits the enzyme pyruvatedehydrogenase kinase, this compound has been used,with limited results, to treat lactic acidosis. The phosphorylation of the a-subunit of the pyruvate dehydrogenasecomponent of the pyruvate dehydrogenase complex bypyruvate dehydrogenase kinase causes complete loss ofenzymatic activity. Describe the theory behind the clinicaluse of dichloroacetate.
What is the overall net reaction for the Pyruvate Dehydrogenase Complex? What enzyme(s) in the Citric Acid Cyclecatalyze(s) substrate-level phosphorylation? What enzyme(s) in the Citric Acid Cyclecatalyze(s) decarboxylation reactions? What enzyme(s) of the Citric Acid Cyclecatalyze(s) reactions in which NAD+or FAD is reduced to NADH or FADH2, respectively?