Principles of Biochemistry, Volume 2 - A. Lehninger 1985

Bioenergetics and Metabolism
Fatty Acid Oxidation in Animal Tissues
Fatty acid oxidation involves two stages

The process of Fatty Acid Oxidation in Cell/35.html">Mitochondria consists of two main stages (Fig. 18-5). In The First stage, two-carbon fragments (in the form of acetyl-CoA) are successively cleaved from the carboxyl end of the fatty acid chain. Each two-carbon fragment is removed via a cycle of enzymatic reactions. For example, The breakdown of the 16-carbon palmitic acid requires seven such repeating cycles, in each of which Enzymes «snip off» one two-carbon fragment as acetyl-CoA from the progressively shortening fatty acid chain. Upon completion of these seven cycles, a final two-carbon fragment remains, also as acetyl-CoA. The net result, therefore, is The conversion of the 16-carbon palmitic acid chain into eight two-carbon fragments in the form of acetyl groups of acetyl-CoA. In each turn of the cycle, The formation of one molecule of acetyl-CoA is accompanied by the removal of four hydrogen atoms from the fatty acid molecule through the action of specific dehydrogenases.

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Fig. 18-5. The two stages of fatty acid oxidation. Stage 1: Oxidation of long-chain Fatty acids yielding acetyl groups in the form of acetyl-CoA. Stage 2: Oxidation of acetyl groups to CO2.

In the second stage of fatty acid oxidation, these acetyl residues of acetyl-CoA are oxidized via The Citric Acid Cycle to CO2 and H2O. This process also takes place within the mitochondria. Consequently, the acetyl-CoA generated by fatty acid oxidation enters the shared final common pathway of oxidation alongside the acetyl-CoA derived from glucose via Pyruvate oxidation (Fig. 17-1).

In both stages of fatty acid oxidation, hydrogen atoms, or their equivalent electrons, are transferred to oxygen via the Mitochondrial Electron Transport chain. This electron flow is coupled to the Oxidative Phosphorylation of ADP to ATP. Therefore, The energy released during both stages of fatty acid oxidation is captured and stored in the form of ATP.



Last update: 06/08/2026

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