The Problem of Stages in Biopoesis 35 



series of tentative pictures of biopoesis. Particularly important is the problem of 

 the origin of the sugars, whether anteriorly or posteriorly, as I have imagined, 

 to that of the amino acids. Another associated problem is the stage at which 

 photosynthesis and oxidation enter the picture. I have tentatively put it after the 

 appearance of the porphyrins. 



I am inclined now, especially after looking at the results of the synthetic experi- 

 ments of Miller, Terenin, Pavlovskaya and Pasynskii, to think that sugar pro- 

 duction must have come rather earlier in biopoesis. Our preoccupation with 

 proteins, quite rightly as the essential biochemical molecule most difficult to 

 synthesize, has led us to pay particular attention to amino acid synthesis. 



However, in the actual synthesis non-nitrogenous substances, mostly vegetable 

 acids, were in fact the main products. Although in these experiments no sugars 

 were produced, this may have been due to the absence of suitable inorganic 

 catalysts. 



As important, but much more characteristic of living systems than the mole- 

 cules they contain, is the mode in which the chemical reactions between them are 

 carried out. This mode we now observe in living organisms is that of reactions 

 arranged in cycles and operated by means of specific enzymes. This cannot have 

 been the original mechanism, if for no more compeUing reason than that the 

 enzymes themselves are produced by the system and are particularly complex 

 bodies even for the simplest reactions. The problem here is to trace the evolution 

 of such facihtating agents for increasing efficiency and speed of action in relation 

 to the kind of substances available at the corresponding stage of molecular 

 evolution. We have to examine the possible nature of proto-enzymes and pro to- 

 co-enzymes. The relation between the reactions and the facHitators is a comple- 

 mentary one. Suitable enzymes must exist at every stage for all the essential 

 reactions at that stage. However, a newly evolved or modified enzyme may in 

 turn modify the reaction or produce new molecules. To some extent every 

 enzyme system will select its own substrates and thus, by reciprocal interaction, 

 biochemical evolution will advance. The modal elements of all organic and 

 biochemical reactions are extremely simple, they all involve the juxtaposition 

 of two particular atoms at hardly more than the sum of their atomic distances 

 apart, the making or breaking of a bond and usually the insertion or removal of 

 a proton. To secure any reaction at all the two components must be present in 

 the appropriate quantum state; to secure that the reaction is only of one kind the 

 molecules of the reagents must come together in the same configuration; to 

 secure rapid reaction that configuration must be easily made and broken. The 

 actions can be direct or mediated by other molecules with reactive groups of 

 which sulphydryl, phosphate and iron ions are the commonest both in the 

 inorganic and biochemical world. 



The efficiency of the primary inorganic catalysts was probably extremely low, 

 but this was of Uttle importance as there could have been at the start no com- 

 petition. Increase in efficiency and speed of reaction must have run in parallel 

 with increasing complexity and size of structure. Two factors intervene in this 

 evolutionary process : greater specificity of the reaction, implying the production 

 of more stable attachment bases suitable for one particular reaction; and greater 



