12.5 What does "omega-3 fatty acids" mean?
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This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.
12.5 What does "omega-3 fatty acids" mean?
Chemists recognise that they should always number carbon chains from the
end with the functional group, so the location of double bonds in
unsaturated fatty acids are numbered from the carboxylic acid end, and
are usually designated by "delta" in their abbreviated names.
Biochemists are more interested in the actual role that chemicals play,
consequently they will consider the position from the end that is important.
In the case of natural fatty acids the double bonds are usually cis
configured, and it is the distance of the first double bond from the
terminal end of the carbon chain that is important. They use "omega" to
signify that the double bond is cis, and they are counting from the other
end. The great advantage is that chain length can be ignored, and compounds
that are subjected to the same biochemical processes are grouped together.
In 1967, the IUPAC/IUB commission responsible for lipid nomenclature
recommended that for unsaturated fatty acids with cis double bonds, that
the "omega" symbol be replaced with "n-x", where n = the length of the
carbon chain, and x is the distance from the terminal end.
Some examples:-
Common Chemical Chemical Biochemical Name Name d = delta o = omega Oleic cis-9-octadecenoic c-C18:1d9 C18:1o9 Elaidic trans-9-octadecenoic t-C18:1d9 - Ricinoleic D-(+)-12-hydroxy-octadec-cis-9-enoic c-C18:1d9-12OH - Linoleic cis-9,12-octadecadienoic c-C18:2d9 C18:2o6 alpha Linolenic cis-9,12,15-octadecatrienoic c-C18:3d9 C18:3o3 gamma Linolenic cis-6,9,12-octadecatrienoic c-C18:3d6 C18:3o6 Arachidonic cis-5,8,11,14-eicosatetraenoic c-C20:4d5 C20:4o6 EPA cis-5,8,11,14,17-eicosapentaenoic c-C20:5d5 C20:5o3 Erucic cis-13-docosenoic c-C22:1d13 C22:1o9 DHA cis-4,7,10,13,16,19-docosahexaenoic c-C22:6d4 C22:6o3
EPA and DHA are widely known as the omega-3 fatty acids present in high
concentrations in marine lipids, and are considered beneficial in diet,
although research is not complete [4,5].
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