Fatty acid biosynthesis is the process by which the body converts acetyl-CoA and malonyl-CoA into fatty acids. The length of the process may depend on whether the fatty acid being formed is straight-chained or branched and how long it is. The process occurs outside the mitochondria in the cell’s cytosol or cytoplasm. In effect, the process is the opposite of fatty acid degradation.
A fatty acid is a carboxylic acid and an organic compound. Such organic compounds come in two forms: saturated and unsaturated. A saturated fatty acid has only single electron bonds between each of the carbon atoms. An unsaturated fatty acid will have one or more double or triple bonds between any two carbon atoms. Fatty acids are taken from adipose tissue and converted into acetyl-CoA in order to produce energy for the cell as part of the citric acid cycle.
The first step of fatty acid biosynthesis is to convert pyruvate into acetyl-CoA. Acetyl-CoA is a molecule used to carry carbon atoms into a cell’s mitochondria. It is an important part of cellular respiration. In the reverse process, the acetyl-CoA transports the carbon atoms back out of the mitochondria. Pyruvate is found within the mitochondria.
Malonyl-CoA is a derivative of coenzyme A and is formed during fatty acid biosynthesis when a carbon dioxide (CO2) molecule is added to a molecule of acetyl-CoA. It is used to lengthen the carbon chain of a fatty acid during fatty acid biosynthesis, but can also be used to transport alpha-ketoglutarate into mitochondria and is an important element of polypeptide biosynthesis. The addition of a carbon dioxide molecule to acetyl-CoA is an irreversible process.
The formation of a straight-chain fatty acid during fatty acid biosynthesis is similar to the oxidization produce during the citric acid cycle. The molecule goes through a four-stage process of condensation, reduction, dehydration and reduction. Each completion of the cycle adds two carbon atoms to the molecule. The process is repeated continuously until the molecule becomes a 16-carbon palmitic acid. Each stage of the process is conducted by an enzyme called Fatty Acid Synthase.
In the subsequent stage of fatty acid biosynthesis, the palmitic acid is converted into palmityl-CoA. This is done using an enzyme system in the cell’s cytoplasm. Unsaturated fatty acids are synthesized by Fatty Acid CoA desaturase enzymes, which produce double bonds. Each double bond is created at a point in the chain specific to the fatty acid being produced, and each of those bonds is produced by an enzyme specific to that location.