194 INTERMEDIATE METABOLISM 



7.— FATS 



A large class of substances occurring in living matter 

 are distinguished by having a greasy consistency, by being 

 insoluble in water but soluble in ether. They are known 

 as Lipoids, and they include the fats, oils, waxes, sterols, 

 phosphatides and cerebrosides. The simplest hpoids are 

 the fats. 



A fat is an ester formed by the condensation of one 

 molecule of glycerine CHgOH . CHOH . CH2OH with three 

 molecules of a higher acid of the ahphatic series — the 

 so-called fatty acids. It is therefore called a triglyceride. 

 Fatty acids are of two kinds : — 



(a) Saturated Fatty Acids. — These are homologues of 

 acetic acid, ha\dng the general formula C„H-2„ + iCOOH. 

 The most commonly occurring members of this group are 

 Palmitic Acid — 



CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2CH2 



CH2COOH 

 or C15H31COOH, 



and Stearic Acid — 



C17H35COOH. 



(6) Unsaturated Fatty Acids. — The commonest member 

 of this group is Oleic acid, which belongs to the oleic series, 

 the members of which have one unsaturated hnkage. 

 General formula — 



C'fll' (in - 1)C00H. 



Oleic acid is — 



CH3(CH2)7CH = CH(CH2)7COOH 



or Ci7H33COOH. 



Fatty acids also occur having a higher degree of unsatu- 



