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Citric Acid Cycle Generates Reductive Equivalents Utilized in Respiration

Citric Acid Cycle Generates Reductive Equivalents Utilized in Respiration. Citric Acid Cycle: A Two Stage Process . Stage One : C 4 + C 2 condensation C 6 tricarboxylic acid Oxidative decarboxylation 2 CO 2 Succinyl CoA Net Result: 2NADH + 2CO 2 + Succinyl CoA.

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Citric Acid Cycle Generates Reductive Equivalents Utilized in Respiration

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  1. Citric Acid Cycle Generates Reductive Equivalents Utilized in Respiration

  2. Citric Acid Cycle: A Two Stage Process Stage One: C4 + C2 condensation C6tricarboxylic acid Oxidative decarboxylation 2 CO2SuccinylCoA Net Result: 2NADH + 2CO2 + SuccinylCoA

  3. C4 + C2 Condensation Reaction Condensation catalyzed by enzyme dimer Citrate Synthase RxN Driver What undesirable side reactions might occur? How can unfavorable side reactions be minimized?

  4. Citrate Synthase Conformational Forms Oxaloacetate binding leads to acetyl CoA binding site formation (partially closed). CitrylCoA formation closes active site for hydrolysis. Production formation opens active site.

  5. Citrate to Isocitrate Conversion via Aconitase Hydroxyl shift for subsequent oxidative decarboxylation How does fluoroacetate function in aconitase catalysis? (Hint: fluoroaceylCoA & fluorocitrate generated first.)

  6. What benefit might Australian plants from the Gastroblonium genus gain in storing the aconitase suicide-inhibitor fluoroacetate?

  7. IsocitrateDehydrogenase: Oxidation and Decarboxylation Oxalosuccinate not released from the enzyme

  8. α-KetoglutarateDehydrogenase: Oxidation and Decarboxylation How similar is α-ketoglutaratedehydrogenase with pyruvatedehydrogenase in terms of substrate components? Reaction mechanism?

  9. Citric Acid Cycle Part Two: Oxaloacetate Regeneration Succinyl Coenzyme A Synthetase couples hydrolysis of Coenzyme A (-33 kJ/mol) with GTP formation (-30 kJ/mol) The energetics works but what about the reaction mechanism?

  10. SuccinylCoA-Sythetase Generates GTP What is the Nu:-, E, and leaving group with GTP generation? Déjà vu with this phosphate exchange?

  11. Oxaloacetate Enzyme Regeneration from Succinate • SuccinateDehydrogenase • Fumerase • MalateDehydrogenase

  12. A Color-Coded Citric Acid Cycle Isocitrate is prochiral Succinate is a symmetric molecule Generated products include: 2CO2 + 3NADH + 1FADH2 + GTP + CoA

  13. Test Your Knowledge When feeding the shown substrate, none of the radiolabel was lost in generating α-ketoglutarate while succinate was devoid of radiolabel. Why were early investigators surprised with these results?

  14. Citric Acid Energetics

  15. Citric Acid Cycle Regulation Points ATP and NADH are indicators of a high energy state ADP an indicator of a low energy state Regulatory sites include: Isocitratedehydrogenase α-Ketoglutaratedehydrogenase Pyruvatedehydrogenase

  16. Citric Acid Cycle is a Source for Biosynthetic Precursors

  17. Citric Acid Cycle Intermediates: Replenished as Metabolites are Drawn Off for Biosynthesis Anapleurotic reactions lead to a replenishment of pathway components (e.g.pyruvatecarboxylase).

  18. Test Your Knowledge Malonate is a competitive inhibitor of succinatedehydrogenase. How will the concentrations of citric acid cycle intermediates change after the addition of malonate? Why is malonate not a substrate for succinatedehydrogenase?

  19. Chapter 18 Problems: 1, 5, 8, and 9

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