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Flashcards in TCA Cycle Deck (12)
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Substrates for TCA Cycle

  • main substrate = acetyl CoA
  • carbon skeletons of sugars, fatty acids and several amino acids enter the citric acid cycle as acetyl CoA
  • acetyl CoA is not the only site where amino acids can enter the cycle


Key intermediates of TCA cycle

  • Citrate
  • α keto-glutarate
  • Succinyl CoA
  • Fumarate
  • Oxaloacetate (and to a lesser extent malate)


Importance of citrate intermediate in TCA cycle

this is the point @ which fatty acid synthesis takes off


Importance of alpha keto-glutarate intermediate in TCA cycle

α keto-glutarate: because this is an important entrance point for a number of amino acids that contribute to gluconeogenesis.



Importance of succinyl CoA intermediate in TCA cycle

Succinyl CoA: because this is an important entrance point for a number of amino acids and for products of the breakdown of fatty acids with an odd number of carbons that contribute to gluconeogenesis.


Importance of fumarate intermediate in TCA cycle

Fumarate: because this is an entrance point for amino acids and because it is a byproduct of the urea cycle.


Importance of oxaloacetate intermediate in TCA cycle


Oxaloacetate (and to a lesser extent malate): because these are involved in the gluconeogenic pathway from pyruvate.


Entry points into TCA for amino acids

  • AA ==> pyrubate ==> Oxaloacetate
  • AA ==> oxaloacetate
  • AA ==> fumarate
  • AA ==> Succinyl CoA
  • AA ==> alpha-ketoglutarate


Main products of TCA cycle

  • The TCA cycle generates NADH, FADH2, GTP.
  • The GTP produced can be used to generate ATP
  • NADH and FADH2 enter the electron transport pathway to also generate ATP


Metabolic role of TCA

  • Oxidation of glucose to pyruvate has not harnessed the energy stored in glucose completely.  
    • TCAC creates more energy from glucose.
  • It also makes biosynthetic precursors (AA’s, nucleotides).  
    • intermediates are continuously channeled into the pathways of amino acid synthesis, fatty acid synthesis, etc.
    • involved in gluconeogenesis @ liver 


TCA ==> gluconeogenesis @ liver

  • In the liver, during fasting, gluconeogenic precursors are converted to malate
  • malate leaves the mitochondria to enter the pathway of gluconeogenesis in the cytosol. 


Key TCA steps for production of NADH, FADH2, & CO2

  • Isocitrate + NAD ==> alpha-ketoglutarate + CO2 + NADH
  • alpha-ketoglutarate + NAD+ ==> Succinyl CoA + CO2 + NADH
  • Succinate + FAD2+ ==> Fumarate + FADH2
  • Malate + NAD+ ==> Oxaloacetate + NADH