Fatty acid Metabolism


This pathway depicts the degradation of palmitic acid (C16:0). Fatty acid degradation and synthesis are relatively simple processes that are essentially the reverse of each other. The process of fatty acid degradation, also known as Beta-Oxidation, converts an aliphatic compound into a set of activated acetyl units (acetyl CoA) that can be processed by the citric acid cycle. An activated fatty acid is first oxidized to introduce a double bond; the double bond is then hydrated to introduce an oxygen; the alcohol is then oxidized to a ketone; and, finally, the four carbon fragment is cleaved by coenzyme A to yield acetyl CoA and a fatty acid chain two carbons shorter. If the fatty acid has an even number of carbon atoms and is saturated, the process is simply repeated until the fatty acid is completely converted into acetyl CoA units. Fatty acid synthesis is essentially the reverse of this process. Because the result is a polymer, the process starts with monomers—in this case with activated acyl group and malonyl units. The malonyl unit is condensed with the acetyl unit to form a four-carbon fragment. To produce the required hydrocarbon chain, the carbonyl must be reduced. The fragment is reduced, dehydrated, and reduced again, exactly the opposite of degradation, to bring the carbonyl group to the level of a methylene group with the formation of butyryl CoA. Another activated malonyl group condenses with the butyryl unit and the process is repeated until a C16 fatty acid is synthesized.

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References

  1. Lehninger, A.L. (2005) Lehninger principles of biochemistry (4 th ed.). New York: W.H Freeman.
  2. Lodish, H., et al. (2004) Molecular cell biology. New York: W.H Freeman.
  3. Salway, J.G. (2004) Metabolism at a glance (3 rd ed.). Alden, Mass. : Blackwell Pub.
  4. Vance, D.E., and Vance, J.E. (2002) Biochemistry of lipids, lipoproteins, and membranes (4 th ed.) Amsterdam ; Boston : Elsevier.