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Anaplerotic Reactions

Anaplerotic Reactions. CH339K. Citric Acid Cycle in Anabolism. Anaplerotic Reactions. ana : back; up; again; re- Plhrow : I fill Anaplerotic reactions refill the pools of Krebs cycle intermediates that would otherwise become depleted. Important Anaplerotic (Replenishing) Reactions.

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Anaplerotic Reactions

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  1. Anaplerotic Reactions CH339K

  2. Citric Acid Cycle in Anabolism

  3. Anaplerotic Reactions ana: back; up; again; re- Plhrow: I fill Anaplerotic reactions refill the pools of Krebs cycle intermediates that would otherwise become depleted.

  4. Important Anaplerotic (Replenishing) Reactions

  5. Pyruvate Carboxylase • Mitochondrial enzyme • Two roles • Gluconeogenesis • Anaplerosis • 4 identical subunits • Biotin cofactor

  6. Role of Biotin in the PyruvateCarboxylase Reaction

  7. PEP Carboxykinase • Cytosolic enzyme active in gluconeogenesis • Mitochondrial enzyme active in anaplerosis

  8. PEP Carboxylase • Mechanism involves pyruvate enolate • Phosphate is transferred from PEP to bicarbonate • Pyruvate enolate then attacks the carboxyphosphate anhydride carbon • Sequesters carbon in some plants

  9. Malic Enzyme • Reductive carboxylation • Uses NADP+ as a cofactor instead of NAD+. • Pyruvate carboxyl reduced to hydroxyl

  10. Transaminations • Every a-amino acid has a conjugate a-keto acid. • Amino and keto conjugates are readily interconverted.

  11. Citric Acid Cycle in Anabolism

  12. Gyoxylate Cycle • Critters can make fat from carbohydrates • Plants, fungi, and some bacteria can make carbohydrates from fats via acetyl-CoA • Use a modified version of the Krebs Cycle • Plants use this to grow from stored oils in seeds • Bacteria use this to grow on simple carbon compounds when carbohydrates are unavailable • Critter exception – some nematodes in early stages can perform

  13. The triffids that ate England were apparently quite dependent on the glyoxylate cycle to assimilate there quivering human prey…

  14. The Glyoxylate Cycle --> gluconeogenesis

  15. 2 Acetyl-CoA + NAD+ + 2H2O --> succinate + 2CoA + NADH + H+ The Glyoxylate Cycle Compare with Citric Acid Cycle Acetyl-CoA + 3NAD+ + FAD + GDP + Pi + 2H2O --> 2CO2 + CoA + 3NADH + 3H+ + FADH2 + GTP

  16. Glyoxylate Cycle Takes Place in Glyoxysomes in Plants

  17. Connections Between Glyoxylate Cycle and Citric Acid Cycle

  18. Isocitrate: An Intermediate Common to the Glyoxylate and Citric Acid Cycles

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