16 



BIOLOGICAL CHEMISTRY 



H 

 C 



or 



HC CH 



C 

 H 



Any group which replaces a hydrogen atom can be placed 

 alongside of the angle corresponding to the carbon atom from 

 which the hydrogen atom has been displaced. The displace- 

 ment of one hydrogen atom from benzine gives rise to the 

 phenyl group. 



FIG. 3. Cholesterol crystals. 



(Redrawn from a photomicrograph.) 



Cholesterol 



Cholesterol is frequently classified with fats under the 

 general term " Lipoid," which also includes the phosphorised 

 fats. The excuse for this classification is that they all dis- 

 solve in ether and other solvents for fats and on extracting 

 tissues with fat solvents they are all extracted together. 



Cholesterol is really a secondary alcohol with a ring forma- 

 tion and the properties of an unsaturated substance. It 

 forms the bulk of the so-called unsaponinable matter associated 

 with fats : it belongs to the terpene series. 



Cholesterol can combine with fatty acids to form cholesterol 

 esters. It crystallises in characteristic flat plates with an 

 indented corner and can be estimated quantitatively by the 



