ORIGIN OF THE FIRST ORGANISMS 381 



turn is transformed into fumaric and then into malic acid, 

 etc. The a-oxoglutaric acid may, however, be transaminated 

 and part of it may leave the cycle by a side route and be 

 converted into glutamic acid which later serves as a ma- 

 terial for the synthesis of proteins. In this way part of the 

 a-oxoglutaric acid is always leaving the cycle irreversibly. In 

 just the same way other keto acids (pyruvic and oxaloacetic 

 acids) react with ammonia, i.e. are aminated directly,*® or 

 are transaminated^" to form alanine and aspartic acid respec- 

 tively. These are later transaminated to form other amino 

 acids. 



The acetic acid arising in the cycle may later take part in 

 the formation of the citric acid of the cycle. ^^ Alternatively 

 it may leave the cycle to serve as the starting material for 

 the formation of fatty acids and other lipids. Oxaloacetic 

 acid and glycine are essential materials for the biosynthesis 

 of purine and pyrimidine bases, and glycine and succinic 

 acid for the construction of porphyrins. Thus, all these bio- 

 synthetic processes which form the basis for the synthesis of 

 living protoplasm are intimately associated with catabolism, 

 from which they obtain their structural starting materials. 



At certain definite points on the cycle there is also libera- 

 tion of energy which is derived from high-energ\' bonds. ^^ The 

 energy of the substances in which these bonds were origin- 

 ally present is transferred to ATP in the mitochondrial 

 system. This, in its turn, activates substances taking a direct 

 part in synthetic reactions. 



Owing to the extremely efficient spatial disposition of the 

 enzymes and coenzymes of the respiratory and energetic 

 complex, their orderly assembly in the mitochondria, the 

 cell achieves a maximal effect in the oxidation of substrates 

 and the transformation of energy. The energy made avail- 

 able in this way is intimately associated with the formation 

 of fragments of molecules which serve as materials for the 

 synthesis of the substances of which the cell is made.^^ The 

 intensity of the oxidative processes in the mitochondria is, 

 therefore, regulated by factors responsible for maintaining 

 the balance between the liberation of energy and the supply 

 of materials required for synthesis. 



The direct synthesis of proteins from amino acids takes 



