Question

Biosynthesis of essential fatty acids linoleic acid

Answer 1

The term omega, as it relates to fatty acids, refers to the terminal carbon atom farthest from the functional carboxylic acid group (–COOH). The designation of a polyunsaturated fatty acid (PUFA) as an omega-3 fatty acid, for example, defines the position of the first site of unsaturation relative to the omega end of that fatty acid . Thus, an omega-3 fatty acid like α-linolenic acid (ALA), which harbors three carbon-carbon double bonds (i.e sites of unsaturation), has a site of unsaturation between the third and fourth carbons from the omega end. There are four major omega-3 fatty acids that are synthesized from precursor fatty acids or ingested in foods and then used by the body. The omega-3 fatty acids are ALA, eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA). Once eaten, the body converts ALA to EPA and then to DPA and finally to DHA as shown in the Figure below. EPA and DHA are the two primary omega-3 PUFAs that serve as bioactive lipids themselves by binding to and activating the G-protein coupled receptor (GPCR) first identified as GPR120 which is encoded by the free fatty acid receptor 4 (FFAR4) gene. In addition to activating a transmembrane GPCR, EPA and DHA are known to bind and activate members of the nuclear receptor family, specifically peroxisome proliferator activated receptor-alpha (PPARα) which is activated by DHA and PPARγ which is activated by EPA. EPA and DHA also serve as important precursors for lipid-derived modulators that are known to contribute to the prevention of cardiovascular diseases, to exert anti-inflammatory effects, to reduce the level of circulating lipids (hypolipedemic effect) while simultaneously increasing lipid catabolism via the activation of the transcriptional co-activator, PPARα, and to reduce the likelihood for non-alcoholic fatty liver disease, NAFLD.


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