BIOCHEMICALLY IMPORTANT COMPOUNDS 205 



It has also been sho^vn that when nucleosides are formed 

 in protoplasm it is not pre-formed purines and pyrimidines 

 which combine with the pentoses, but the much simpler 

 compounds Avhich we have already mentioned, which serve 

 as the starting materials for their formation. ^"^ 



Of course one must be very careful here, as in all other 

 cases, in drawing analogies between what happens in the 

 living organism and what might have taken place in the 

 waters of the primaeval ocean. Nevertheless we can construct 

 on this basis hypotheses, though only very rough ones, about 

 the primary formation of nucleosides, as the ribose or desoxy- 

 ribose required can be produced in the ways which we have 

 described for other carbohydrates. 



The possibility of the incorporation of the third com- 

 ponent of nucleotides, orthophosphoric acid, at first glance 

 presents no difficulties. The question of the primary, abio- 

 genic formation of compounds of phosphorus with organic 

 substances is, however, extremely complicated and poorly 

 understood. 



In the powerfully reducing conditions which prevailed on 

 the surface of the Earth in the earliest epoch of its existence, 

 when carbon, nitrogen and sulphur w^ere present in the forms 

 of methane, ammonia and hydrogen sulphide, phosphorus 

 must also have entered into the primitive atmosphere, though 

 only in part, in the form of hydrogen phosphide, which 

 reacted with the hydrocarbons to form substituted phos- 

 phines. 



Unfortunately we only have very old and extremely 

 general information to the effect that the action of electric 

 discharges on mixtures of phosphine and ethylene leads to 

 the occurrence of extensive condensation reactions.^"* Changes 

 of this kind can also come about on ultraviolet irradiation, 

 for phosphines absorb radiations having wavelengths in the 

 region of 2,315-2,290 A. In the outer layers of the atmo- 

 sphere, however, the phosphines must have been oxidised 

 by the oxygen derived from the photolysis of water with the 

 formation of phosphine oxides and alkylphosphinic acids. ^°^ 

 This may be regarded as the formation of phosphorous acid 



