Arachidonic acid fatty acids

See also Linoleic Acid, Linolenic Acid, Arachidonic Acid, Fatty Acid Desaturation... 

Correct answer = E. Prostaglandins are synthesized from arachidonic acid. Arachidonic acid is synthesized from linoleic acid, an essential fatty acid obtained by humans from dietary lipids. The teenager would be able to synthesize all other compounds, but presumably in somewhat depressed amounts. 

Arachidonic acid Eicosatetraenoic acid cbh31co2h Essential fatty acid... 

Phospholipids — arachidonic acid - Arachidonic acid metabolites appear not to be stored within cells. Their biosynthesis depends upon the appearance of substrate at or near the microsomal synthetase complex(es). According to current thinking, arachidonic acid is stored in the phospholipid fraction of the cell from which the free fatty acid is liberated by the action of a phospholipase... 

CYP4 A Primarily endogenous arachidonic and fatty acids Laurie acid Arachidonic acid None Yes Its induction is associated with peroxisomal proliferation and epigenetic carcinogenicity in rodents... 

The most abundant and therefore the most common precursor of the eicosanoids is arachidonic acid (eicosatetraenoic acid, w6,20 4,A5,8,ll,14), a polyunsaturated fatty acid with 20 carbons and 4 double bonds (see Fig. 35.1). It is esterified to phospholipids located in the lipid bilayer that constitutes the plasma membrane of the cell. Because arachidonic acid cannot be synthesized de novo in the body, the diet must contain arachidonic acid or other fatty acids from which arachidonic acid can be produced. The major dietary precursor for arachidonic acid synthesis is the essential fatty acid linoleate, which is present in plant oils (see Chapter 33). 

The connections between endoeannabinoids and eicosanoids occur in several areas. First, there is the obvious common structural feature based on arachidonic acid (eicosatetraeneoic acid) as well as other long-chain polyunsaturated aeids. In the case of the eicosanoids, all of the members are either cyclization or oxidation produets of arachidonic acid whereas in the endocannabinoids the fatty acid structure is preserved (Figure 8.1). 

It is clear that oxylipin formation occurs in these organisms, and that the production is sensitive to life stage. It is difficult to interpret the significance of these oxylipins to the reproductive biology of Dipodascopsis because virtually all work has been done with exogenous arachidonic acid. Arachidonic acid comprised only 0.1% of the endogenous fatty acids in Dipodascopsis while linoleic and linolenic acids represented 25.6 and 3.3% respectively [27]. It would be interesting to see if 3-HPODE and aspirin-sensitive linoleic-acid-based oxylipins are produced in Dipodascopsis. 

Incorporation of from l C-arachidonate into fatty acids, including 22 5, was similar in the deficient and supplemented ani-... 

PI, a major class of phospholipids, important as intracellular messengers and protein anchor substances Lipid A) in membranes. In animal tissues they often contain high proportions of arachidonic acid eicosatetraenoic acid). Complete hydrolysis gives glycerol, fatty acids (2 moles), phosphoric acid and myo-inositol. See also phosphoinositides. 

CifiHjjOi. A fatly acid which is easily oxidized in air.-It occurs widely, in the form of glycerides, in vegetable oils and in mammalian lipids. Cholesieryl linoleale is an important constituent of blood. The add also occurs in lecithins. Together with arachidonic acid it is the most important essential fatty acid of human diet. 

Arachidonic acid gets its name from arachidic acid the saturated C20 fatty acid isolated from peanut (Arachts hypogaea) oil... 

Prostaglandins arise from unsaturated C20 carboxylic acids such as arachidonic acid (see Table 26 1) Mammals cannot biosynthesize arachidonic acid directly They obtain Imoleic acid (Table 26 1) from vegetable oils m their diet and extend the car bon chain of Imoleic acid from 18 to 20 carbons while introducing two more double bonds Lmoleic acid is said to be an essential fatty acid, forming part of the dietary requirement of mammals Animals fed on diets that are deficient m Imoleic acid grow poorly and suffer a number of other disorders some of which are reversed on feed mg them vegetable oils rich m Imoleic acid and other polyunsaturated fatty acids One function of these substances is to provide the raw materials for prostaglandin biosynthesis... 

Detailed accounts of the biosynthesis of the prostanoids have been pubUshed (14—17). Under normal circumstances arachidonic acid (AA) is the most abundant C-20 fatty acid m vivo (18—21) which accounts for the predominance of the prostanoids containing two double bonds eg, PGE2 (see Fig. 1). Prostanoids of the one and three series are biosynthesized from dihomo-S-linolenic and eicosapentaenoic acids, respectively. Concentrations ia human tissue of the one-series precursor, dihomo-S-linolenic acid, are about one-fourth those of AA (22) and the presence of PGE has been noted ia a variety of tissues (23). The biosynthesis of the two-series prostaglandins from AA is shown ia Eigure 1. These reactions make up a portion of what is known as the arachidonic acid cascade. Other Hpid products of the cascade iaclude the leukotrienes, lipoxins, and the hydroxyeicosatetraenoic acids (HETEs). Collectively, these substances are termed eicosanoids. 

The prostaglandins (qv) constitute another class of fatty acids with aUcycHc structures. These are of great biological importance and are formed by i vivo oxidation of 20-carbon polyunsaturated fatty acids, particularly arachidonic acid [27400-91-5]. Several prostaglandins, eg, PGE [745-65-3] have different degrees of unsaturation and oxidation when compared to the parent compound, prostanoic acid [25151 -18-9]. 

Some fatty acids are not synthesized by mammals and yet are necessary for normal growth and life. These essential fatty aeids include llnoleic and y-linolenic acids. These must be obtained by mammals in their diet (specifically from plant sources). Arachidonic acid, which is not found in plants, can only be synthesized by mammals from linoleic acid. At least one function of the essential fatty acids is to serve as a precursor for the synthesis of eicosanoids, such as... 

Mammals can add additional double bonds to unsaturated fatty acids in their diets. Their ability to make arachidonic acid from linoleic acid is one example (Figure 25.15). This fatty acid is the precursor for prostaglandins and other biologically active derivatives such as leukotrienes. Synthesis involves formation of a linoleoyl ester of CoA from dietary linoleic acid, followed by introduction of a double bond at the 6-position. The triply unsaturated product is then elongated (by malonyl-CoA with a decarboxylation step) to yield a 20-carbon fatty acid with double bonds at the 8-, 11-, and 14-positions. A second desaturation reaction at the 5-position followed by an acyl-CoA synthetase reaction (Chapter 24) liberates the product, a 20-carbon fatty acid with double bonds at the 5-, 8-, IT, and ITpositions. 

FIGURE 25.15 Arachidonic acid is synthesized from linoleic acid in enkaryotes. This is the only means by which animals can synthesize fatty acids with double bonds at positions beyond C-9. 

Eicosanoids, so named because they are all derived from 20-carbon fatty acids, are ubiquitous breakdown products of phospholipids. In response to appropriate stimuli, cells activate the breakdown of selected phospholipids (Figure 25.27). Phospholipase Ag (Chapter 8) selectively cleaves fatty acids from the C-2 position of phospholipids. Often these are unsaturated fatty acids, among which is arachidonic acid. Arachidonic acid may also be released from phospholipids by the combined actions of phospholipase C (which yields diacyl-glycerols) and diacylglycerol lipase (which releases fatty acids). 

Animal cells can modify arachidonic acid and other polyunsaturated fatty acids, in processes often involving cyclization and oxygenation, to produce so-called local hormones that (1) exert their effects at very low concentrations and (2) usually act near their sites of synthesis. These substances include the prostaglandins (PG) (Figure 25.27) as well as thromboxanes (Tx), leukotrienes, and other hydroxyeicosanoic acids. Thromboxanes, discovered in blood platelets (thrombocytes), are cyclic ethers (TxBg is actually a hemiacetal see Figure 25.27) with a hydroxyl group at C-15. 

More than LOO different fatty acids are known, and about 40 occur widely. Palmitic acid (C ) and stearic acid (Cjy) are the most abundant saturated fatty adds oleic and linoleic acids (both Care the most abundant unsaturated ones. Oleic acid is monounsaturated since it has only one double bond, whereas linoleic, linolenic, and arachidonic acids are polyunsaturated fatty acids because they have more than one double bond. Linoleic and linolenic... 

CYP5 synthesizes thromboxane A2, a fatty acid in the arachidonic acid cascade that causes platelet aggregation. Aspirin prevents platelet aggregation because it blocks the cyclooxygenases COX1 and COX2 which catalyze the initial step of the biotransformation of arachidonic acid to thromboxane and prostaglandins. 

---