The second stage of aerobic respiration is the Krebs cycle, which occurs within thematrix 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 twomolecules 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
