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2011-12-04 19:14:35

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  1. What is the Citric Acid Cycle?
    A specific mechanism to produce NADH and FADH2 for the electron transport chain
  2. How is glycolysis linked to TCA?
    Glycolysis provides AcetylCoA from pyruvate. Pyruvate condenses with oxaloacetate to form citrate.
  3. What enzyme catalyzes this reaction:
    Pyruvate + CoA + NAD+ <---> AcetylCoA + Co2 + NADH
    The pyruvate dehydrogenase complex
  4. what are the five required CoFactors for the pyruvate dehydrogenase complex?
    • Lipoic Acid
    • Coenzyme A (sCoA)
    • Thiamine pyrophosphate (TPP/B1)
    • Nicotinamide dinucleotide (NAD+)
    • FAD
  5. What are the three enzymes that make up the pyruvate dehydrogenase complex?
    • E1: Pyruvate Dehydrogenase
    • E2: Dihydrolipoyl transacetylase
    • E3: Dihydrolipoyl dehydrogenase
  6. What is the mechanism of action for the pyruvate dehydrogenase complex?
    • In E1 Carbon 2 of pyruvate is decarboxylated by TPP creating the CO2 product and hydroxyethyl-TPP.
    • The acetyl group is then transferred to S-Lipoamide in E1.
    • In E2, the acetyl mo iety is transferred to CoA producing Acetyl CoA.
    • In E3, lipoamide is oxidized by FAD, then NAD+ by FADH2 to recycle the lipoamide forming NADH and H+.
  7. What are the products of the pyruvate dehydrogenase complex?
    Acetyl CoA, NADH+H+ and CO2
  8. How many moles of acetyl CoA are transferred into the mitochondria per mole of glucose?
  9. What is step 1 of the TCA cycle?
    • The condensation of OAA and Acetyl CoA to form Citrate via citrate synthase.
    • Driven by hydrolysis of CoA - nearly irreversinle.
  10. What is step 2 of the TCA cycle?
    • Citrate <---> CisAconitate <---> Isocitrate via aconitase.
    • OH group on C2 relocates to C3.
    • dehydration, then hydration.
  11. What is step 3 of the TCA cycle?
    • Isocitrate ---> a-Ketoglutarate via isocitrate dehydrogenase.
    • Nad+ is reduced to NADH and CO2 is produced (2/glucose).
  12. What is step 4 of the TCA cycle?
    • a-KG ---> Succinyl CoA via a-KG dehydrogenase complex.
    • Dehydrogenation rxn.
    • NAD+ is reduced to NADH and CO2 from C5 is produced in a similar mech. as pyruvate dehydrogenase complex.
  13. What is step 5 of the TCA cycle?
    • Succinyl CoA <---> Succinate via Succinyl CoA Synthase.
    • GTP + ADP <---> ATP + GDP, favorable sCoA hydrolysis is linked to unfavorable GTP formation.
  14. TCA only forms 2 moles of GTP/glucose. Is this a waste of time?
    No because each mole of glucose produces 6 NADH and 2 FADH2 which is important for the ETC.
  15. How many NADH are made for the ETC from glycolysis and TCA? Where are they formed?
    • 10.
    • 2 from glycolysis
    • 2 during acetyl CoA formation
    • 2 during a-KG formation
    • 2 during Succinyl CoA formation
    • 2 during OAA formation.
  16. What is step 6 of the TCA cycle?
    • Succinate <---> Fumarate via succinate dehydrogenase.
    • FAD <---> FADH2
  17. What does malonate inhibit?
    Fumarate production. Malonate is a competitive inhibitor for succinate dehydrogenase.
  18. What is step 7 of the TCA cycle?
    • Fumarate <---> Malate via fumarase.
    • This is a steroselective addittion of H2O across a double bond.
  19. What is step 8 of the TCA cycle?
    • Malate <---> Oxaloacetate via malate dehydrogenase.
    • NAD+ <---> NADH. This is an oxidation.
  20. What are the enzymes for each step of the TCA cycle and what kind of reaction do they catalyze?
    • 1) Citrate Synthase: condensation
    • 2) Aconitase: dehydration/hydration
    • 3) Isocitrate dehydrogenase: Oxidative decarboxylation
    • 4) a-KG dehydrogenase complex: oxidative decarboxylation
    • 5) Succinyl CoA synthetase: substrate level phos
    • 6) succinate dehydrogenase: oxidation
    • 7) Fumarase: hydration
    • 8) Malate dehydrogenase: oxidation
  21. What are the nine TCA intermediates?
    • 1) Citrate
    • 2) CisAconitate
    • 3) Isocitrate
    • 4) a-KG
    • 5) Succinyl-CoA
    • 6) Succinate
    • 7) Fumarate
    • 8) Malate
    • 9) Oxaloacetate
  22. What must occur in order for bionsynthesis to happen? (OAA ---> cell components)
    Energy level must be high. OAA is needed to condense with Acetyl-CoA to produce e- carriers for ETC
  23. what is the reaction that produces OAA directly from pyruvate?
    • Pyruvate + ATP + CO2 ---> ADP + OAA via pyruvate carboxylase.
    • Requires biotin to carry CO2.
  24. What are the key TCA control points?
    • Pyruvate dehydrogenase down regulated by high energy charge, ATP, NADH and feedback by Acetyl CoA.
    • Citrate synthase allosterically inhibited by ATP and NADH, activated by ADP.
  25. What are the secondary control points for TCA?
    • Isocitrate dehydrogenase inhibited by ATP, allosterically activated by ADP.
    • a-KG dehydrogenase feedback inhibition by succinyl COA and NADH.
  26. What does the DHAP/G3P shuttle do?
    Brings electrons into the ETC.
  27. What is the corey cycle?
    Lactate from working muscle tissue is transported via the blood stream to the liver where it is converted baack to glucose to be transported to other tissues.
  28. What does biotin do?
    Biotin is a coenzyme that carries CO2. CO2 can be added to another carbon onto a small carbon chain.
  29. How is pyruvate converted back to PEP in gluconeogenesis?
    Pyruvate <--> OAA <--> PEP
  30. What is activated Biotin?
    Biotin w/CO2 attached is unstable. Activation of Biotin requires ATP
  31. By what mechanism is OAA converted to PEP?
    OAA + H20 + GTP <---> GDP + Pi + CO2 + PEP via PEP Carboxy Kinase
  32. What is the malate shuttle?
    • NADH carrier if going into mitochondria, makes sugars for gluconeogenisis if coming out.
    • Pyruvate <---> OAA <---> Malate <---> OAA <---> PEP <---> Glucose
  33. What drives gluconeogenesis and glycolysis?
    • Gluconeogenisis: Plenty of ATP, Citrate, F-1,6BP
    • Glycolysis: Plenty of AMP, ADP
  34. What is this?
  35. What is this?
    Acetyl CoA
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  40. What is this?
    Succinyl CoA
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