. Biochemistry of plants and animals, an introduction. Biochemistry. 92 GENERAL BIOCHEMISTRY WAXES These compounds, like the fats, are simple lipides. They differ from glycerides, however, in that they are esters of high-molecular- weight alcohols instead of glycerol. In general, these alcohols are long-chain monohydric alcohols, such as cetyl alcohol (CicH;j;^OH), melissyl alcohol (CgoHdOH), and carnaubyl alcohol (C24H49OH). Sometimes the alcohol involved is dihydric as in the case of cocceryl alcohol (CgoHco (OH)2). Waxes may be animal or vegetable in origin. While their solubilities are sim
. Biochemistry of plants and animals, an introduction. Biochemistry. 92 GENERAL BIOCHEMISTRY WAXES These compounds, like the fats, are simple lipides. They differ from glycerides, however, in that they are esters of high-molecular- weight alcohols instead of glycerol. In general, these alcohols are long-chain monohydric alcohols, such as cetyl alcohol (CicH;j;^OH), melissyl alcohol (CgoHdOH), and carnaubyl alcohol (C24H49OH). Sometimes the alcohol involved is dihydric as in the case of cocceryl alcohol (CgoHco (OH)2). Waxes may be animal or vegetable in origin. While their solubilities are similar to those of fats, the waxes, in general, have appreciably higher melting points. They may be saponified like the fats but with much greater difficulty. The waxes are quite widespread in nature, but as a rule they never occur abun- dantly. Many natural waxes are mixtures of esters. Beeswax, which is one of the best known of this group, contains melissyl alcohol (CsoHgiOH), combined with palmitic (C1CH32O2), cerotic (C26H52O2), and melissic (C30H60O2) acids. Waxes are found in thin layers covering the surfaces of the stems or stalks of many plants, where they function as a protective waterproof coating. The "bloom" on many fruits has been identified as a wax or a wax-like substance. STEROLS Although the word sterol literally means solid alcohol, the term has been limited in recent years to include only certain cyclic alcohols of high molecular weight. Sterols contain a characteristic cyclic nucleus made up of three six-membered rings and one five-membered ring which are arranged and numbered as shown in the following diagram:. Sterols occur abundantly in plant and animal tissues as well as in yeasts and molds. On the other hand, they have not been shown to occur in bacteria. Although all sterols have the characteristic steroid nucleus shown, they differ markedly from each other with respect to. Please note that these images are extracted from scanned page images th
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