Krebs Cycle

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•  In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating

    carbon dioxide

The second stage of aerobic respiration is the Krebs cycle, which occurs within the matrix of the mitochondria

  • The Krebs cycle is also commonly referred to as the citric acid cycle or the tricarboxylic acid (TCA) cycle

In the Krebs cycle, acetyl CoA transfers its acetyl group to a 4C compound (oxaloacetate) to make a 6C compound (citrate)

  • Coenzyme A is released and can return to the link reaction to form another molecule of acetyl CoA

Over a series of reactions, the 6C compound is broken down to reform the original 4C compound (hence, a cycle)

  • Two carbon atoms are released via decarboxylation to form two molecules of carbon dioxide (CO2)
  • Multiple oxidation reactions result in the reduction of hydrogen carriers (3 × NADH + H+ ; 1 × FADH2)
  • One molecule of ATP is produced directly via substrate level phosphorylation

As the link reaction produces two molecules of acetyl CoA (one per each pyruvate), the Krebs cycle occurs twice

  • Per glucose molecule, the Krebs cycle produces:  4 × CO2  ;  2 × ATP  ;  6 × NADH + H+  ;  2 × FADH2

The Krebs Cycle

krebs cycle