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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
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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)
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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)
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Isocitrate
- -formed from aconitate using aconitase (requires H2O)
- -third reaction in TCA
- -undergoes oxidative decarboxylation by isocitrate dehydrogenase to form α-Ketoglutarate and CO2 (first C lost in cycle) and NADH
- -irreversible reaction
- -inhibited by ATP
- -activated by ADP and Ca2+
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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+
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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
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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
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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
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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
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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)
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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
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Regulation of TCA
- -reactions that yield energy are regulated
- -generally product inhibition (high energy inhibition) low energy activation
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