THE CHEMISTRY OF LIFE 47 



compounds from inorganic substances. Today we even synthesize 

 such complex organic chemicals as hormones and vitamins. Hence, 

 we can no longer consider such a generalized statement as accurate. A 

 chemical analysis of organic compounds reveals the fact that carbon 

 is always an important part of such compounds. We have, therefore, 

 come to think of organic compounds as those containing carbon as a 

 part of their make-up. Contrariwise, we say that the inorganic com- 

 pounds are those which do not contain carbon, but we must modify 

 this latter statement slightly for there are a few inorganic compounds, 



H H H H H H H 



I I I I I II 



H— C — C— C — C — C — C — H H— C— C — OH 



I I I I I II II 



000000 HH 



1 I I I I 

 H H H H H 



Simple sugar (alucose) Ethyl alcohol 



H H 



I I II 



H — N — C— C — OH 



I 

 H 



Glycine (on amino acid ) 



Fig. 3.5. Structural formulas of some common organic compounds. Note the im- 

 portant, central position of carbon in each of these. 



the carbonates, that do contain carbon. The carbon atom is so con- 

 structed that it can form a greater variety of compounds than is possible 

 for any other element. The variety of organic chemicals, therefore, 

 is very great. Several organic chemicals are shown in their structural 

 formulas in Fig. 3.5. A structural formula shows the relationship of 

 the various atoms which go to make up a molecule. Note that the 

 carbon atoms serve as a central point of attachment for many of the 

 other atoms in such molecules. 



Chemical Composition of Protoplasm 



Water. About 60 to 99 per cent of animal protoplasm is composed 

 of water. The exact amount of this substance varies with different 

 types of cells and different species of animals, but a typical average 

 is about 80 per cent. Water is an indispensable constituent of living 



