Some chemistry sources define Arachidonic acid to designate any of the eicosatetraenoic acids. However, almost all writings in biology, medicine and
nutrition limit the term to all-cis-5,8,11,14-eicosatetraenoic acid.
Arachidonic acid is a polyunsaturated fatty acid
present in the phospholipids (especially phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositides) of membranes of the body's cells,
and is abundant in the brain.
It is also involved in cellular signaling as a second messenger.
It is the source of several other molecules with specific roles.
Arachidonic acid is one of the essential fatty acids required by most mammals. Some mammals lack the ability to-or have a very limited capacity
to-convert Linoleic acid
into arachidonic acid,
making it an essential part of their diet. Since little or no Arachidonic acid is found in plants, such animals are obligate carnivores; the cat is
a common example.