SELECTED PAPERS 



the chaos of dissolved substances could then continue until the supply 

 of one or more of the specific building blocks had become exhausted. 



There are indications from cell physiology that the nucleic acids of 

 the nucleus also give rise to the formation of the chemically somewhat 

 different ribonucleic acids that are dispatched into the protoplasm 

 surrounding the nucleus, where they function as catalysts for the syn- 

 thesis of proteins. Although our understanding of the mechanism of 

 these processes is still limited, it remains possible that, during the 

 hundreds of millions of years that are available, local conditions have 

 fortuitously been realized under which could be produced a system 

 composed of desoxyribose nucleic acid - ribose nucleic acid - protein. 

 Now the process of ordering the organic matter with the production of 

 self-multiplying primeval living entities could proceed until the supply 

 of some of the indispensable building blocks of the system had been 

 depleted. 



We have already seen that modern genetic research has convincing- 

 ly shown the occurrence in microbial cells of spontaneous modifica- 

 tions, with a surprisingly high frequency, and referable to an alteration 

 in the arrangement of the building blocks in the nucleic acids of the 

 genes. On the other hand, investigations of the microbial mutations 

 induced by irradiations have demonstrated that the various elemen- 

 tary reactions to which metabolism can be reduced are individually 

 determined by specific genes. In this manner one can assume - and 

 here I follow the line of reasoning developed by Horowitz - that an 

 incidental mutation in a gene of a primeval living entity has caused 

 this system to acquire the property of manufacturing the lacking 

 building block from another kind of molecule with a closely corre- 

 sponding composition. At this point metabolism proper made its en- 

 trance on the scene of life. Consecutive mutations, each one adding a 

 new reaction step to the existing ones, thus caused the genesis of sys- 

 tems that became progressively more independent of the nature of 

 organic substances present in the medium. Starting with a system that 

 originally was heterotrophic with respect to every one of its building 

 blocks, a situation that at present is still approximated by the oblig- 

 atorily parasitic micro-organisms, there would gradually have arisen 

 systems that became autotrophic with reference to an increasing num- 

 ber of building blocks. Ultimately this would have led to a completely 

 autotrophic metabolism such as that which to-day we still encounter, 



5 U 



