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The process continues until all of the carbons in the fatty acid are turned into acetyl CoA. This acetyl-CoA then enters the mitochondrial tricarboxylic acid cycle (TCA cycle). Both the fatty acid beta-oxidation and the TCA cycle produce NADH and FADH 2, which are used by the electron transport chain to generate ATP.
After activation by ATP, once inside the mitochondria, the β-oxidation of a fatty acids occurs via four recurring steps: Oxidation by FAD; Hydration; Oxidation by NAD + Thiolysis; Production of acyl-CoA and acetyl-CoA; The final product of β-oxidation of an even-numbered fatty acid is acetyl-CoA, the entry molecule for the citric acid cycle. [3]
Fatty acids are broken down to acetyl-CoA by means of beta oxidation inside the mitochondria, whereas fatty acids are synthesized from acetyl-CoA outside the mitochondria, in the cytosol. The two pathways are distinct, not only in where they occur, but also in the reactions that occur, and the substrates that are used.
CoA is acetylated to acetyl-CoA by the breakdown of carbohydrates through glycolysis and by the breakdown of fatty acids through β-oxidation. Acetyl-CoA then enters the citric acid cycle, where the acetyl group is oxidized to carbon dioxide and water, and the energy released is captured in the form of 11 ATP and one GTP per acetyl group.
The resulting acyl-CoA cross the mitochondria membrane and enter the process of beta oxidation. The main products of the beta oxidation pathway are acetyl-CoA (which is used in the citric acid cycle to produce energy), NADH and FADH. [16] The process of beta oxidation requires the following enzymes: acyl-CoA dehydrogenase, enoyl-CoA hydratase ...
However, if the amounts of acetyl-CoA generated in fatty-acid β-oxidation challenge the processing capacity of the TCA cycle; i.e. if activity in TCA cycle is low due to low amounts of intermediates such as oxaloacetate, acetyl-CoA is then used instead in biosynthesis of ketone bodies via acetoacetyl-CoA and β-hydroxy-β-methylglutaryl-CoA .
Fatty acids are broken down to acetyl-CoA by means of beta oxidation inside the mitochondria, whereas fatty acids are synthesized from acetyl-CoA outside the mitochondrion, in the cytosol. The two pathways are distinct, not only in where they occur, but also in the reactions that occur, and the substrates that are used.
Acetyl-CoA is then used in the citric acid cycle while FADH2 and NADH are sent to the electron transport chain. [8] These intermediates all end up providing energy for the body as they are ultimately converted to ATP. [8] Example of Beta Oxidation using Stearic Acid. Beta oxidation, as well as alpha-oxidation, also occurs in the peroxisome. [1]