MECHANISM OF METABOLISM. 145 



form. Growth is the typical manifestation of anabolism. It is the 

 formation of new cells from dead organic or inorganic matter, and it 

 means the formation of all the compounds necessary for cell life. Of 

 all the substances found in the cell, practically none are contained in the 

 food, and it is wonderful that in such a small unit as a microbial cell, 

 there are contained the powers of making protoplasm, enzymes, nuclear 

 bodies, chromatin-bodies, the substance of the cell wall and probably 

 many other unknown compounds. All these complex substances are 

 generally made from simple food compounds as amino-acids, carbo- 

 hydrates and others. 



These synthetic processes of the cell will, like most endothermic 

 processes, take place only if energy is provided. This condition is usually 

 fulfilled in the living cell, due to the fermenting processes going on con- 

 tinuously. There is a strange interaction between anabolism and intra- 

 cellular fermentation proceeding in the protoplasm and this linking 

 together of destructive and constructive reaction is the basis of life 

 processes. The life processes decompose certain substances, the energy 

 liberated allows the formation of protoplasm, which again liberates 

 energy. Thus a continuous formation of protoplasm is secured. 



An explanation of anabolism based upon chemical experiments is 

 not possible at the present time. In the study of intra- cellular destruction 

 it is possible to trace most processes back to enzymic action. There 

 our knowledge ceases because the nature and mode of action of 

 enzymes is unknown. In the study of anabolism our knowledge has 

 not even progressed so far. The most promising explanation at present 

 is based upon the reversibility of enzymic action. 



REVERSIBILITY OF ENZYMIC ACTION. Chemical reactions between 

 organic compounds proceed quite rapidly at first, then become slower 

 and slower until the reaction stops entirely. The reaction is not com- 

 plete at the time it reaches an equilibrium. If the equilibrium is disturbed 

 by adding more of the reagents, the process will continue. If, however, 

 the products of reaction are added, the reverse process will take place. 

 Reactions between organic compounds can proceed either way, depending 

 upon the relative concentrations of the reacting substances. The stand- 

 ard exaniple is esterification. Acetic acid plus alcohol gives ester plus 

 water, 



CH 3 COOH+ CH 3 CH 2 OH<=>CH 3 COO CH 2 CH 3 + H 2 O 



Acetic acid Alcohol Ester 



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