Lecture25-2007 - Citric Acid Cycle II Lecture 25 Chapter...

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1 Citric Acid Cycle II Lecture 25 Chapter 16-4, 16-5 CAC is an Amphibolic Pathway • Amphibolic: both catabolic and anabolic functions. – Catabolic: oxidation of acetate to CO 2 . – Anabolic: intermediates serve as precursors to other molecules. • Depletion of intermediates for anabolic pathways creates a problem for catabolism: slows CAC. Cataplerotic reactions: “empty” CAC Anaplerotic reactions: “fill” CAC
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2 Cataplerotic reactions: Glutamate dehydrogenase: Cataplerotic reactions: Aspartyl aminotransferase Anaplerotic reactions • Amino acid breakdown • Odd-chain fatty acid breakdown • Pyruvate carboxylase (biotin): Pyruvate + CO 2 + ATP + H2O --> OAA + ADP + Pi If insufficient OAA in cycle, Acetyl-CoA builds up. Acetyl-CoA activates pyruvate carboxylase, makes more OAA. Cataplerotic reactions: “empty” CAC Anaplerotic reactions: “fill” CAC
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3 Anaplerotic reactions • Amino acid breakdown • Odd-chain fatty acid breakdown • Pyruvate carboxylase (biotin): Pyruvate + CO 2 + ATP + H2O --> OAA + ADP + Pi If insufficient OAA in cycle, Acetyl-CoA builds up. Acetyl-CoA activates pyruvate carboxylase, makes more OAA. OAA ß-keto acid: decarboxylation is energetically favorable OAA -----> Pyr + CO 2 ! G o’ < 0 Pyruvate carboxylase (biotin) Coupled reaction: use energy in ATP to drive forward the
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Lecture25-2007 - Citric Acid Cycle II Lecture 25 Chapter...

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