26.3 Fatty Acid Biosynthesis 1019 in may be saturated or it can contain one or more double bonds. When double present, they are almost always cis. Acyl groups containing 14-20 carbon ate ter of glycerol, the fat substi- he most abundant in triacylglycerols PROBLEM 26. 1 What fatty acids are produced on hydrolysis of 2-oleyl-1, 3 esters of sucrose in which the yl groups are derived from distearylglycerol? What other triacylglycerol gives the same fatty acids and in thefatty acidsOlestra has many same proportions as 2-oleyl-1, 3-distearylglycerol? of the physical and taste the major source of trans fats comes from the processing of natural fats and oils. In the For more about olestra, see course of hydrogenating some of the double bonds in a triacylglycerol, stereoisomeriza- Journal of chemical educa. tion can occur, converting cis double bonds to trans. Furthermore, the same catalysts that tion, pp370-372 promote hydrogenation promote the reverse process--dehydrogenation-by which new double bonds, usually trans, are introduced in the acyl group Fatty acids occur naturally in forms other than as glyceryl triesters, and we'll see numerous examples as we go through the chapter. One recently discovered fatty acid the Journal of Chemical Edu. derivative is anandamide tains an article entitled Trans Fatty Acids. Anandamide Anandamide is an ethanolamine(h,NCH, Ch,oh) amide of arachidonic acid(see table 26.1). It was isolated from pigs brain in 1992 and identified as the substance that nor- mally binds to the cannabinoid receptor. "The active component of marijuana, entists had long wondered what compound in the body was the natural substrate binding site. Anandamide is that compound, and it is now probably more appropriate to Other than that both are speak of cannabinoids binding to the anandamide receptor instead of vice versa. Anan- lipids, there are no obvious damide seems to be involved in moderating pain. Once the identity of the"endogenous structural similarities be. cannabinoid"was known, scientists looked specifically for it and found it in some sur- prising places--chocolate, for example Fatty acids are biosynthesized by way of acetyl coenzyme A. The following sec- tion outlines the mechanism of fatty acid biosynthesis 26.3 FATTY ACID BIOSYNTHESIS We can describe the major elements of fatty acid biosynthesis by considering the for- mation of butanoic acid from two molecules of acetyl coenzyme A. The"machinery responsible for accomplishing this conversion is a complex of enzymes known as fatty acid synthetase. Certain portions of this complex, referred to as acyl carrier protein (ACP), bear a side chain that is structurally similar to coenzyme A. An important early step in fatty acid biosynthesis is the transfer of the acetyl group from a molecule of acetyl coenzyme A to the sulfhydryl group of acyl carrier protein. CH3 CSCOA+HS一ACP—>CH3CS-ACP+ HSCOA S-Acetyl acyl Coenzyme a A Back Forward Main MenuToc Study Guide ToC Student o MHHE Website26.3 Fatty Acid Biosynthesis 1019 chain may be saturated or it can contain one or more double bonds. When double bonds are present, they are almost always cis. Acyl groups containing 14–20 carbon atoms are the most abundant in triacylglycerols. PROBLEM 26.1 What fatty acids are produced on hydrolysis of 2-oleyl-1,3- distearylglycerol? What other triacylglycerol gives the same fatty acids and in the same proportions as 2-oleyl-1,3-distearylglycerol? A few fatty acids with trans double bonds (trans fatty acids) occur naturally, but the major source of trans fats comes from the processing of natural fats and oils. In the course of hydrogenating some of the double bonds in a triacylglycerol, stereoisomeriza￾tion can occur, converting cis double bonds to trans. Furthermore, the same catalysts that promote hydrogenation promote the reverse process—dehydrogenation—by which new double bonds, usually trans, are introduced in the acyl group. Fatty acids occur naturally in forms other than as glyceryl triesters, and we’ll see numerous examples as we go through the chapter. One recently discovered fatty acid derivative is anandamide. Anandamide is an ethanolamine (H2NCH2CH2OH) amide of arachidonic acid (see Table 26.1). It was isolated from pig’s brain in 1992 and identified as the substance that nor￾mally binds to the “cannabinoid receptor.” The active component of marijuana, 9 -tetrahydrocannabinol (THC), must exert its effect by binding to a receptor, and sci￾entists had long wondered what compound in the body was the natural substrate for this binding site. Anandamide is that compound, and it is now probably more appropriate to speak of cannabinoids binding to the anandamide receptor instead of vice versa. Anan￾damide seems to be involved in moderating pain. Once the identity of the “endogenous cannabinoid” was known, scientists looked specifically for it and found it in some sur￾prising places—chocolate, for example. Fatty acids are biosynthesized by way of acetyl coenzyme A. The following sec￾tion outlines the mechanism of fatty acid biosynthesis. 26.3 FATTY ACID BIOSYNTHESIS We can describe the major elements of fatty acid biosynthesis by considering the for￾mation of butanoic acid from two molecules of acetyl coenzyme A. The “machinery” responsible for accomplishing this conversion is a complex of enzymes known as fatty acid synthetase. Certain portions of this complex, referred to as acyl carrier protein (ACP), bear a side chain that is structurally similar to coenzyme A. An important early step in fatty acid biosynthesis is the transfer of the acetyl group from a molecule of acetyl coenzyme A to the sulfhydryl group of acyl carrier protein. O CH3CSCoA Acetyl coenzyme A O CH3CS ACP S-Acetyl acyl carrier protein HSCoA Coenzyme A HS ACP Acyl carrier protein N H OH O Anandamide Instead of being a triacyl es￾ter of glycerol, the fat substi￾tute olestra is a mixture of hexa-, hepta-, and octaacyl esters of sucrose in which the acyl groups are derived from fatty acids. Olestra has many of the physical and taste properties of a fat but is not metabolized by the body and contributes no calories. For more about olestra, see the April 1997 issue of the Journal of Chemical Educa￾tion, pp. 370–372. The September 1997 issue of the Journal of Chemical Edu￾cation (pp. 1030–1032) con￾tains an article entitled “Trans Fatty Acids.” Other than that both are lipids, there are no obvious structural similarities be￾tween anandamide and THC. 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