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Metabolism of Carbohydrates: Glycolysis and Gluconeogenesis , Citric Acid Cycle [Tricarboxylic acid (TCA) cycle] [Krebs cycle]
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Pyruvate Dehydrogenase Links Glycolysis to the Citric Acid Cycle
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The Citric Acid Cycle Oxidizes Two-Carbon Units
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Entry to the Citric Acid Cycle and Metabolism Through It Are Controlled
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The Citric Acid Cycle Is a Source of Biosynthetic Precursors
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The citric acid cycle is the final common pathway for the oxidation of fuel molecules.
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Most fuel molecules enter the cycle as acetyl coenzyme A.
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The function of the citric acid cycle is the harvesting of high energy electrons from carbon fuels.
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The citric acid cycle itself neither generates a large amount of ATP nor includes oxygen as a reactant.
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The citric acid cycle constitutes the first stage in cellular respiration, the removal of high-energy electrons from carbon fuels in the form of NADH and FADH2 (left).
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These electrons reduce O2 to generate a proton gradient (red pathway),
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which is used to synthesize ATP (green pathway). The reduction of O2 and the synthesis of ATP constitute oxidative phosphorylation.
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Pyruvate dehydrogenase component
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1 |
TPP
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Dihydrolipoyl transacetylase
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2 |
Lipoamide
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Dihydrolipoyl dehydrogenase
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3 |
FAD
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Oxidative decarboxylation of pyruvate
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Transfer of acetyl group to CoA
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3 |
Regeneration of the oxidized form of lipoamide
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1-Carbanion of TPP Carbanion of TPP + Pyruvate -> Hydroxyethyl-TPP |
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1-Hydroxyethyl-TPP + Lipoamide -> Carbanion of TPP + Acetyllipoamide(high energy) |
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2-Coenzyme A+Acetyllipoamide -> Acetyl CoA(high energy)+Dihydrolipoamide |
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3-Dihydrolipoamide+FAD->Lipoamide+FADH2--NAD+-->FAD+NADH+H+ |
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