Arachidonic acid is an omega-6 fatty acid with the chemical formula C20H32O2. In physiological literature, it is given the name 20:4(n-6). Its systematic chemical name is all-cis-5,8,11,14-eicosatetraenoic acid and its molecular weight is 304.5. Chemically, arachidonic acid is a carboxylic acid with a 20-carbon chain and four cis double bonds; the first double bond is located at the sixth carbon from the omega end. 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 that is present in the phospholipids (especially phosphatidylethanolamine, phosphatidylcholine and phosphatidylinositides) of membranes of the body's cells, and is abundant in the brain. It is a precursor in the production of eicosanoids: the prostaglandins, thromboxanes, prostacyclin and the leukotrienes (through enzymes including cyclooxygenase, lipoxygenase and peroxidase). The production of these derivatives, and their action in the body, are collectively known as the arachidonic acid cascade; see Essential fatty acid interactions for details.
Arachidonic acid is freed from phospholipid molecule by the enzyme phospholipase A2. It is also involved in cellular signaling as a second messenger.
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 obligatory carnivores; the cat is a common example.