Cells typically contain large amounts of C18 and C20 fatty acids. Longer chain fatty acids are derived from either dietary sources or from elongation of C16-CoA or C18-CoA formed by the cytoplasmic fatty acid synthetase system. All of the fatty acids needed can be synthesized from palmitate (C16:0) except the essential polyunsaturated fatty acids such as linoleate and linolenate. To create longer, shorter, oxidized, reduced fatty acids, palmitic acid is subjected to enzymatic reactions by reductases, hydroxylases, elongases and mixed function oxidases. There are 3 major processes that modify palmitic acid: elongation, desaturation, and hydroxylation. Elongation of fatty acids may occur at endoplasmic reticulum where fatty acid molecules of length up to C24 may be produced. Mitochondrial elongation may result in fatty acids up to C16 in length. Fatty acid elongation in mitochondria is essentially the reverse of beta-oxidation for fatty acid oxidation. In particular, both pathways make use of acetyl-CoA acyltransferase, 3-hydroxyacyl-CoA dehydrogenase and enoyl-CoA hydratase. The final step of fatty acid elongation uses enoyl-CoA reductase (not part of the beta-oxidation pathway). The mitochondrial pathway is important for elongating fatty acids containing 14 or fewer carbon atoms. Fatty acids with aliphatic tails of less than six carbons are short-chain fatty acids (SCFA). Medium chains (MCFA) have a six to twelve carbon tail and large chains (LCFA) have a tail with greater than twelve carbons. Very long chain fatty acids (VLCFA) have a tail with greater than twenty-two carbons.

Fatty Acid Elongation In Mitochondria References