Citric Acid Cycle

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  1. Acetyl Co-A
    • -formed from pyruvate using pyruvate dehydrogenase complex
    • [-activated by AMP, CoA, NAD+(low nrg) and Ca2+ -inhibited by ATP, acetyl-CoA, NADH, Fatty acids(high nrg)]
    • -first reactant in cycle
    • -condensation reaction(requires water)
    • -requires H2O 
    • -forms two products, Citrate using citrate synthase(not energy requiring) and CoA-SH(leaves cycle)
    • -non reversible reaction
    • -inhibited by NADH, succinyl-CoA, citrate, ATP
    • -activated by ADP
  2. Citrate
    • -formed from Acetyl-CoA using citrate synthase (requires water)
    • -2A reaction in TCA
    • -is dehydrated using aconitase 
    • -products are cis-Aconitase and H2O
    • -reversible reaction
    • -same enzyme is used in reaction 3 as well
    • -one of two 6-C acids in cycle (aconitase)
  3. Aconitate
    • -formed from Citrate using aconitase(requires H2O)
    • -2B reaction in TCA
    • -is hydrated by aconitase to form Isocitrate (requires H2O)
    • -reversible reaction
    • -same enzyme as in reaction 2
    • -one of two 6-C acids in cycle (citrate)
  4. Isocitrate
    • -formed from aconitate using aconitase (requires H2O)
    • -third reaction in TCA
    • -undergoes oxidative decarboxylation by isocitrate dehydrogenase to form α-Ketoglutarate and CO(first C lost in cycle) and NADH
    • -irreversible reaction
    • -inhibited by ATP
    • -activated by ADP and Ca2+ 
  5. α-Ketoglutarate
    • -formed from isocitrate using isocitrate dehydrogenase (NADH and CO2 given off as well)
    • -fourth reaction in TCA
    • -only 5C acid in cyle
    • -undergoes oxidative decarboxylation using α-ketoglutarate dehydrogenase complex to form succinyl-CoA
    • -requires CoA-SH(biproduct of reaction 1 to form citrate, also formed in rxn 5)
    • -gives off CO2 and NADH
    • -irreversible
    • -inhibited by succinyl-CoA and NADH
    • -activated by Ca2+
  6. Succinyl-CoA
    • -formed from α-ketoglutarate using α-ketoglutarate dehydrogenase complex (NADH and CO2 given off as biproducts)
    • -fifth reaction in TCA
    • -undergoes phosphate level phosphorylation by succinyl-CoA synthetase(energy requiring)
    • -requires GDP(or ADP) and inorganic phosphate 
    • -produces succinate, Co-A SH(biproduct of first reaction and required in 4th rxn) and GTP(or ATP)
    • -reversible reaction
  7. Succinate
    • -formed from succinyl-CoA by succinyl-CoA synthetase(nrg requiring ADP or GDP and Pi)
    • -6th rxn in TCA
    • -undergoes dehydrogenation by succinate dehydrogenase to form fumarate and biproduct of FADH2
    • -reversible rxn
  8. Fumarate
    • -formed from succinate by succinate dehydrogenase (biproduct of FADH2)
    • -7th rxn in TCA
    • -undergoes hydration (rxn requires H2O) by fumarase to malate 
    • -reversible rxn
  9. Malate
    • -formed from fumarate in hydration rxn(H2O requiring) by fumarase 
    • -8th rxn in TCA
    • -is dehydrogenated by malate dehydrogenase to oxaloacetate with biproduct of NADH
    • -reversible reaction
  10. Oxaloacetate
    • -formed from malate by malate dehydrogenase with biproduct of NADH
    • -"final product" on TCA, but can be converted to citrate by citrate synthase(like acetyl CoA)
  11. Energy Yielding Reactions
    • -reaction 3-NADH-from isocitrate to α-ketoglutarate(enz:isocitrate dehydrogenase)
    • -reaction 4-NADH-from α-ketoglutarate to succinyl-CoA (enz:α-ketoglutarate dehydrogenase complex)
    • -reaction 5-ATP or GTP-from succinyl-CoA to succinate (enz:succinyl-CoA synthetase) 
    • -reaction 6-FADH-from succinate to fumarate (enz:succinate dehydrogenase) 
    • -reaction 8-NADH-from Malate to oxaloacetate (enz: malate dehydrogenase) 
    • -NOTICE-all "dehydrogenase" enzymes create energy either NADH, or FADH2 and require the acceptor molecules to complete rxn
    • -total production of 10 ATP equivalent
  12. Regulation of TCA
    • -reactions that yield energy are regulated 
    • -generally product inhibition (high energy inhibition) low energy activation
Card Set:
Citric Acid Cycle
2013-04-11 05:03:32
BMSC 230

citric acid cycle
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