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Pyruvate Oxidation: Pyruvate Dehydrogenase and the TCA Cycle

Pyruvate Oxidation: Pyruvate Dehydrogenase and the TCA Cycle. Aerobic “respiration” in mitochondria: important for ATP synthesis and a source of intermediates for other biochemical pathways pyruvate (C 3 H 3 O 3 ) + 4 NAD + + FAD + GDP + Pi + 2H 2 O

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Pyruvate Oxidation: Pyruvate Dehydrogenase and the TCA Cycle

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  1. Pyruvate Oxidation: Pyruvate Dehydrogenase and the TCA Cycle

  2. Aerobic “respiration” in mitochondria: important for ATP synthesis • and a source of intermediates for other biochemical pathways • pyruvate (C3H3O3) + 4 NAD+ + FAD + GDP + Pi + 2H2O • 3 CO2 + 4 NADH + 3 H+ + FADH2 + GTP • First step: pyruvate dehydrogenase

  3. Pyruvate dehydrogenase function

  4. Acetyl-CoA is oxidized in the citric acid (Kreb’s, TCA) cycle

  5. TCA Cycle

  6. Recap TCA cycle: • acetyl-CoA(C2H3O-CoA) + 3 NAD+ + FAD + GDP + Pi + 2H2O • CoA-SH + 2 CO2 + 3 NADH + 3 H+ + FADH2 + GTP • Include pyruvate oxidation: • pyruvic acid(C3H4O3) + 4 NAD+ + FAD + GDP + Pi + 2H2O • 3 CO2 + 4 NADH + 4 H+ + FADH2 + GTP • Complete oxidation of the pyruvate carbons • Reduction of 4 NAD+ and one FAD • Phosphorylation of one GDP

  7. The TCA cycle is a source of biosynthetic precursors But what happens when intermediates are removed from the cycle?

  8. Without intermediates, the cycle stops! “Anaplerotic” reactions replenish the intermediates. Pyruvate + CO2 + ATP + H2O OAA + ADP + Pi + 2 H+

  9. A modification of the TCA cycle (glyoxylate cycle) lets plants and bacteria make carbohydrates from fats. to glucose isocitric lyase malate synthase

  10. Summary • The TCA cycle gives complete oxidation of the pyruvate carbons. • And reduction of 4 NAD+ and one FAD. • And phosphorylation of one GDP. • The TCA cycle is a source of biosynthetic precursors. • Pyruvate carboxylase and the glyoxylate cycle replenish precursors • Replenishment of NAD + and FAD are also essential.

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