6. The AG of the citric acid cycle reaction catalyzed by succinyl-CoA synthetase is approximately 0 kJ/mol. Which of the following statements explains why we would expect this reaction to be highly exergonic, but why the overall AG ≈ 0 in reality. A) The reaction cleaves a thioether linkage, and the released free energy is used to generate a new thioester linkage in a product molecule. B) The reaction cleaves a thioester linkage, and the released free energy is used to generate GTP. C) The reaction cleaves a thioester linkage, and the released free energy is used to generate a new thioester linkage in a product molecule. D) None of the above

6. The AG of the citric acid cycle reaction catalyzed by succinyl-CoA synthetase is approximately 0 kJ/mol. Which of the following statements explains why we would expect this reaction to be highly exergonic, but why the overall AG ≈ 0 in reality. A) The reaction cleaves a thioether linkage, and the released free energy is used to generate a new thioester linkage in a product molecule. B) The reaction cleaves a thioester linkage, and the released free energy is used to generate GTP. C) The reaction cleaves a thioester linkage, and the released free energy is used to generate a new thioester linkage in a product molecule. D) None of the above

Organic Chemistry

9th Edition

ISBN:9781305080485

Author:John E. McMurry

Publisher:John E. McMurry

Chapter29: The Organic Chemistry Of Metabolic Pathways

Section29.SE: Something Extra

Problem 24MP: One of the steps in the pentose phosphate pathway for glucose catabolism is the reaction of xylulose...

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Aldolase catalyzes the glycolytic reaction The standard free-energy change for this reaction in the direction written is +23.8 kJ/mol. The concentrations of the three intermediates in the hepatocyte of a mammal are: fructose 1,6-bisphosphate, 1.4 × 10−5 M; glyceraldehyde 3-phosphate, 3 × 10−6 M; and dihydroxyacetone phosphate, 1.6 ×10−5 M. At body temperature (37 °C), what is the actual free-energy change for the reaction?
TPP is a coenzyme for transketolase, the enzyme that catalyzes the conversion of a ketopentose (xylulose5-phosphate) and an aldopentose (ribose-5-phosphate) to an aldotriose (glyceraldehyde-3-phosphate) and a ketoheptose (sedoheptulose-7-phosphate). Notice that the total number of carbons in the reactants and products is the same (5 + 5 = 3 + 7). Propose a mechanism for this reaction.
TPP is a coenzyme for transketolase, the enzyme that catalyzes the conversion of a ketopentose (xylulose- 5-phosphate) and an aldopentose (ribose-5-phosphate) to an aldotriose (glyceraldehyde-3-phosphate) anda ketoheptose (sedoheptulose-7-phosphate). Notice that the total number of carbons in the reactants and products is the same (5 + 5 = 3 + 7). Propose a mechanism for this reaction.
Given the following information on reduction potentials, calculate the standard free energy in kJ/mol based on your understanding of electron transfer through the pyruvate dehydrogenase complex. Round to nearest whole number. Lipoamide + 2H+ + 2e- → dihydrolipoamide ∆εο = -0.29 FAD + 2H+ + 2e- → FADH2 ∆εο = −0.01
One of the steps in the pentose phosphate pathway for glucose catabolism is the reaction of xylulose 5-phosphate with ribose 5-phosphate in the presence of a transketolase to give glyceraldehyde 3-phosphate and sedoheptulose 7-phosphate. (a) The first part of the reaction is nucleophilic addition of thiamin diphosphate (TPP) ylide to xylulose 5-phosphate, followed by a retro-aldol cleavage to give glyceraldehyde 3-phosphate and a TPPcontaining enamine. Show the structure of the enamine and the mechanism by which it is formed. (b) The second part of the reaction is addition of the enamine to ribose 5-phosphate followed by loss of TPP ylide to give sedoheptulose 7-phosphate. Show the mechanism.
Identify the following intermediate in the citric acid cycle, and tell whether it has R or S stereochemistry:
Which of the reactions are spontaneous (favorable)? 1)DHAP↽−−⇀glyceraldehyde-3-phosphateΔ?=3.8 kJ/mol 2)L-malate+NAD+⟶oxaloacetate+NADH+H+Δ?=29.7 kJ/mol- 3) glutamate+NAD++H2O⟶NH+4+α-ketoglutarate+NADH+H+Δ?=3.7 kcal/ 4) C6H13O9P+ATP⟶C6H14O12P2+ADPΔ?=−14.2KJ/mol 5) −Rh(I)C2H6Δ?=−150.97 kJ/molC2H4+H2→Rh(I)C2H6ΔG=−150.97 kJ/mol 6) C4H4O5⟶C4H2O4+H2OΔ?=3.1 kJ/mol
For the following carbohydrates, please indicate the TRUE alternative: (a) The carbohydrate V is reducing and is hydrolyzed by an enzyme of the type β galactosidase (b) Carbohydrate VI is not reducing or mutating. (c) Carbohydrates I and IV have β-glucosidic bond, while carbohydrate II has α-glucosidic bond. (d) Carbohydrate III is neither reducing nor hydrolyzed by an α-type enzyme such as maltase. (e) Carbohydrate I is reducing and mutating.
An aldopentose "O", is oxidized with HNO3 to a diacid "P" which is optically active. The compound "O", is also degraded to an aldotetrose "Q" which undergoes another oxidation to an optically inactive diacid "R". Assuming that "O" has the configuration D-(4R); what are the structures of "O" to "R"?
1.In the mitochondria, enzymes attached to the membrane use the ______________ to produce a ____________ difference and thus an electrical potential. Making the transfer of _______________ possible a. pH, flow of electrons, hydrogens b. pH, electron flow, oxygen c. electron flow, pH, hydrogens d. Electron flow, pH, Oxygen 2.Which of the following sugars can be a substrate for hexokinase? a.glucose b.fructose c.mannose d.all these e.none of those
3) The enzyme aldolase catalyzes the conversion of fructose-1,6-diphosphate (FDP)to dihydroxyacetone phosphate (DHAP) and glyceraldehide-3-phosphate (G3P). Thereaction isFDP ⇄ DHAP + G3P , ∆rG0(298.15 K) = 23.8 kJ mol−1In red blood cells the concentration of these species are [FDP] = 35 µM, [DHAP] =130 µM, and [G3P] = 15 µM. (Remember that 1.0 µM = 1.0 × 10−6 mol L−1. Thestandard state for reactions in solution can be taken as c0 = 1.0 mol L−1).Calculate ∆rG in a red blood cell at 25 0C. Will the reaction occur spontaneouslyin the cell at this temperature?
The enzyme d-amino acid oxidase has avery high turnover number because the d-amino acids are potentially toxic. The KM for the enzyme is in the range of 1 to2 mM for the aromatic amino acids and in the range of 15 to20 mM for such amino acids as serine, alanine, and the acidicamino acids. Which of these amino acids are the preferred substrates for the enzyme?