2l8 NUTRITION AND METABOLISM 



compounds. All these complex substances are generally made from 

 simple food compounds as amino-acids, carbohydrates 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 continuously. There is a strange interaction between 

 anabolism and intra-cellular fermentation proceeding in the pro- 

 toplasm 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 proto- 

 plasm, 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 destruc- 

 tion 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 or 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 complete 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 standard 

 example is esterification. Acetic acid plus alcohol gives ester plus 

 water, 



CHsCOOH + CH 3 CH 2 OH^CH 3 COOCH2CH3 + H 2 O. 



Acetic acid Alcohol Ester 



The process goes to a certain equilibrium and stops. If ester is mixed 

 with water, it gives acid plus alcohol, until the same equilibrium is 

 reached. If acid and alcohol are added to a system in equilibrium, more 

 ester will be formed. If ester is added, more alcohol and acetic acid 



