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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 



