Fatty acid
Malonyl-CoA is then involved in a repeating series of reactions that lengthens the growing fatty acid chain by two carbons at a time. Almost all natural fatty acids, therefore, have even numbers of carbon atoms. When synthesis is complete the free fatty acids are nearly always combined with glycerol (three fatty acids to one glycerol molecule) to form triglycerides, the main storage form of fatty acids, and thus of energy in animals. However, fatty acids are also important components of the phospholipids that form the phospholipid bilayers out of which all the membranes of the cell are constructed (the cell wall, and the membranes that enclose all the organelles within the cells, such as the nucleus, the mitochondria, endoplasmic reticulum, and the Golgi apparatus).
Omega-3 fatty acid
Omega−3 fatty acids, also called ω−3 fatty acids or "n"−3 fatty acids, are polyunsaturated fatty acids (PUFAs) characterized by a double bond three atoms away from the terminal methyl group. They are widely distributed in nature, being important constituents of animal lipid metabolism, and they play an important role in the human diet and in human physiology. The three types of omega−3 fatty acids involved in human physiology are α-linolenic acid (ALA), found in plant oils, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both commonly found in marine oils. Marine algae and phytoplankton are primary sources of omega−3 fatty acids. Common sources of plant oils containing ALA include walnut, edible seeds, clary sage seed oil, algal oil, flaxseed oil, Sacha Inchi oil, "Echium" oil, and hemp oil, while sources of animal omega−3 fatty acids EPA and DHA include fish, fish oils, eggs from chickens fed EPA and DHA, squid oils, and krill oil.
Omega−3 fatty acids are important for normal metabolism. Mammals are unable to synthesize omega−3 fatty acids, but can obtain the shorter-chain omega−3 fatty acid ALA (18 carbons and 3 double bonds) through diet and use it to form the more important long-chain omega−3 fatty acids, EPA (20 carbons and 5 double bonds) and then from EPA, the most crucial, DHA (22 carbons and 6 double bonds). The ability to make the longer-chain omega−3 fatty acids from ALA may be impaired in aging. In foods exposed to air, unsaturated fatty acids are vulnerable to oxidation and rancidity. Dietary supplementation with omega−3 fatty acids does not appear to affect the risk of death, cancer or heart disease. Furthermore, fish oil supplement studies have failed to support claims of preventing heart attacks or strokes or any vascular disease outcomes.
The terms "ω–3 ("omega–3") fatty acid" and "n–"3 "fatty acid" are derived from organic nomenclature. One way in which a fatty acid is named is determined by the location of the first double bond, counted from the methyl end, that is, the omega (ω-) or the "n"- end (see illustration). In general terminology using either "n–x" or ω–"x", the dash is a minus sign (although it is never read as such), and the number "n–x" (or ω–"x") refers to the locant of the double bond linking two carbon atoms. Thus, in omega"–"3 fatty acids in particular, there is a double bond located on the carbon numbered 3 lower than the highest carbon number. By example, α-linolenic acid (ALA; illustration) is an 18-carbon chain having three double bonds, the first being located at the third carbon from the methyl end of the fatty acid chain, known as the "n" end. Thus, α-linolenic acid is a polyunsaturated "n−3" (omega-3) fatty acid with lipid number, 18:3 (18 carbon atoms, 3 double bonds).