• Pyruvic acid, the product of glycolysis, cannot enter the Krebs cycle directly. In a preparatory step; it must lose one molecule of Co₂ and become a two-carbon compound. This process is called decarboxylation. The two carbon compound called an acetyl group, attaches to Coenzyme a through a high-energy bond, the resulting complex is known as Acetyl Coenzyme A. During this reaction, pyruvic acid is also oxidized and NAD⁺ is reduced to NADH.

• Oxidation of one glucose molecule produces 2 molecules of pyruvic acid, so for each molecule of glucose, 2 molecules of Co₂ are released in the preparatory step, 2 molecules of NADH are produced, and 2 molecules of Acetyl Coenzyme A are formed.

• As Acetyl coenzyme A enters the Krebs cycle, CoA detaches from the acetyl group. The two carbon acetyl group combines with a four carbon compound called oxaloacetic acid to form six carbon compound, called citric acid. This synthesis reaction requires energy, which is provided by the cleavage of the high energy bond between the acetyl group and CoA. The formation of citric acid is the first step in the Krebs cycle.

• Two decorboxylation reactions take place in the Krebs cycle while converting Isocitric acid to α – Ketoglutaric acid and this to succinyl CoA.

• Altogether 3 decarboxylation reactions take place and hence all three carbon atoms in pyruvic acid are eventually released as Co₂ by the Krebs cycle. This represents the conversion to Co₂ by all 6 carbon atoms contained in the original glucose molecule.

• Oxidation-reduction reactions also occurs, where NAD⁺ and FAD picks up hydrogen atoms to be reduced to NADH and FADH₂.

• On the whole, for every two molecules of acetyl CoA that enter the cycle, 4 molecules of Co₂ and 6 for pyruvic acid are liberated by decorboxylation, 6/8 moelucles of NADH and 2 moleucles of FADH₂ are produced by oxidation-reduction reactions, and two molecules of ATP are generated by substrate- level phosphorylation. Many of the intermediates in the Krebs cycle also play a role in other pathways, especially in amino acid biosynthesis.

• Reduced coenzymes NADH and FADH₂ are the important products of the Krebs cycle because they contain most of the energy originally stored in glucose. During the next phase of respiration, a series of reductions indirectly transfers the energy stored in those coenzymes to ATP. These reactions are collectively called Electron transport chain.