1024 CHAPTER TWENTY-SIX Lipids 26.5 WAXES Waxes are water-repelling solids that are part of the protective coatings of a number of living things, including the leaves of plants, the fur of animals, and the feathers of birds hey are usually mixtures of esters in which both the alkyl and acyl group are unbranched and contain a dozen or more carbon atoms. Beeswax, for example, contains the ester triacontyl hexadecanoate as one component of a complex mixture of hydrocar- bons. alcohols. and esters CH3(CH2)14COCH,(CH2)28CH3 Triacontyl hexadecanoate PROBLEM 26.5 Spermaceti is a wax obtained from the sperm whale. It contains among other materials, an ester known as cetyl palmitate, which is used as an emollient in a number of soaps and cosmetics. The systematic name for cetyl palmitate is hexadecyl hexadecanoate. Write a structural formula for this sub- Fatty acids normally occur naturally as esters; fats, oils, phospholipids, and waxes all are unique types of fatty acid esters. There is, however, an important class of fatty acid derivatives that exists and carries out its biological role in the form of the free acid This class of fatty acid derivatives is described in the following section 26.6 PROSTAGLANDINS Research in physiology carried out in the 1930s established that the lipid fraction of emen contains small amounts of substances that exert powerful effects on smooth mus- cle. Sheep prostate glands proved to be a convenient source of this material and yielded a mixture of structurally related substances referred to collectively as prostaglandins. We now know that prostaglandins are present in almost all animal tissues, where they carry out a variety of regulatory functions Prostaglandins are extremely potent substances and exert their physiological effects at very small concentrations. Because of this, their isolation was difficult, and it was not until 1960 that the first members of this class, designated PGE and PGFla(Figure 26.5), were obtained as pure compounds. More than a dozen structurally related prostaglandins have since been isolated and identified. All the prostaglandins are 20-carbon carboxylic acids and contain a cyclopentane ring. All have hydroxyl groups at C-ll and C-15(for the numbering of the positions in prostaglandins, see Figure 26.5). Prostaglandins belong ing to the F series have an additional hydroxyl group at C-9, and a carbonyl function is COOH COOH CH FIGURE 26.5 Struc HO tures of two representative Prostaglandin el Prostaglandin Fla bering scheme is illustrated PGEj (PGFla) in the structure of PGE1 Back Forward Main MenuToc Study Guide ToC Student o MHHE Website1024 CHAPTER TWENTY-SIX Lipids 26.5 WAXES Waxes are water-repelling solids that are part of the protective coatings of a number of living things, including the leaves of plants, the fur of animals, and the feathers of birds. They are usually mixtures of esters in which both the alkyl and acyl group are unbranched and contain a dozen or more carbon atoms. Beeswax, for example, contains the ester triacontyl hexadecanoate as one component of a complex mixture of hydrocar￾bons, alcohols, and esters. PROBLEM 26.5 Spermaceti is a wax obtained from the sperm whale. It contains, among other materials, an ester known as cetyl palmitate, which is used as an emollient in a number of soaps and cosmetics. The systematic name for cetyl palmitate is hexadecyl hexadecanoate. Write a structural formula for this sub￾stance. Fatty acids normally occur naturally as esters; fats, oils, phospholipids, and waxes all are unique types of fatty acid esters. There is, however, an important class of fatty acid derivatives that exists and carries out its biological role in the form of the free acid. This class of fatty acid derivatives is described in the following section. 26.6 PROSTAGLANDINS Research in physiology carried out in the 1930s established that the lipid fraction of semen contains small amounts of substances that exert powerful effects on smooth mus￾cle. Sheep prostate glands proved to be a convenient source of this material and yielded a mixture of structurally related substances referred to collectively as prostaglandins. We now know that prostaglandins are present in almost all animal tissues, where they carry out a variety of regulatory functions. Prostaglandins are extremely potent substances and exert their physiological effects at very small concentrations. Because of this, their isolation was difficult, and it was not until 1960 that the first members of this class, designated PGE1 and PGF1 (Figure 26.5), were obtained as pure compounds. More than a dozen structurally related prostaglandins have since been isolated and identified. All the prostaglandins are 20-carbon carboxylic acids and contain a cyclopentane ring. All have hydroxyl groups at C-11 and C-15 (for the numbering of the positions in prostaglandins, see Figure 26.5). Prostaglandins belong￾ing to the F series have an additional hydroxyl group at C-9, and a carbonyl function is O CH3(CH2)14COCH2(CH2)28CH3 Triacontyl hexadecanoate O HO CH3 COOH Prostaglandin E1 (PGE1) HO HO Prostaglandin F1 (PGF1) HO 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 CH3 COOH HO FIGURE 26.5 Struc￾tures of two representative prosta-glandins. The num￾bering scheme is illustrated in the structure of PGE1. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website