94 LIPIDES (fats and RELATED SUBSTANCES) 



Note particularly the high carbon number of most of the components 

 listed, and the fact that the hydrocarbons all contain odd rather than 

 even numbers of carbon atoms. Although lanolin is one of the most 

 common and important waxes, it is not included in Table 4-8 because 

 of its unique composition. It contains over 20 unusual branched chain 

 acids and hydroxyacids combined as esters with a variety of alcohols, 

 among which are ceryl alcohol, cholesterol, other sterols, and at least 

 two alcohols of the triterpene type. Another unusual type of wax con- 

 stituent, reportedly present in Chinese urushi wax, is represented by two 

 of the higher dibasic acids, H00C(CHo)i8C00H, and HOOC(CH2)2o- 

 COOH. 



STEROLS 



Sterols are solid, cyclic alcohols usually containing 27-29 carbon atoms, 

 17 of which are arranged in a characteristic ring system consisting of 

 three six-membered rings and one five-membered ring (sjee Fig. 4-2). 

 Over thirty sterols have been found in nature. They occur in the tissues 

 of animals, in plants, abundantly in yeasts and molds, but apparently not 

 at all in bacterial cells. Some are saturated; others contain one, two 

 or three double bonds. Various side chains and one or more hydroxyl 

 groups complete the sterol structure (see formulas of cholesterol below, 

 and ergosterol, p. 213). The sterols may occur free, or combined with 

 fatty acids as esters, or with carbohydrates as glycosides. 



Fig. 4-2. Diagram and numbering of the steroid ring system. 



Several types of substance closely related to the sterols are of particular 

 biological importance. They include the bile acids, sex hormones (p. 

 292), adrenal cortical hormones (p. 290), vitamins D (p. 210), several 

 heart-stimulating drugs {e.g., digitalis) , saponins, and others. The sterols 

 and their related substances are collectively designated as steroids. All 

 contain the characteristic steroid ring system (Fig. 4-2). 



Cholesterol 



This substance is the characteristic sterol of higher animals. Although 

 present in every cell of the body, it is most abundant in egg yolk, animal 

 fats like cream and butter, cod liver oil, and especially in nerve and brain 

 tissue. In fact, the concentration in the human brain may reach the 



