BIOSYNTHESIS OF PROTEINS 285 



thetic reactions. In fact the kinetic conditions which are 

 very important for any biosynthesis, the relative rates of dif- 

 ferent processes, the organisation of protoplasm in space as 

 well as in time, give great flexibility to the biosynthesis. This 

 leads to the formation, not of individual proteins, the mole- 

 cules of which are identical with one another, but of extensive 

 families of proteins which are very like one another. 



This would be hard to achieve by rigid synthesis on a 

 matrix. It would be as though the same type could be used 

 to print several newspapers which, although they were of the 

 same political persuasion, nevertheless had a different scope 

 and arrangement of their articles. This suggestion was also 

 discounted by Gamow in his latest paper. Gamow^"^ regards 

 the variability of the proteins which are synthesised as a 

 possible means of biological evolution, although he gives no 

 explanation of the mechanism of this phenomenon. 



To pursue the typographical analogy, set type is needed 

 to form the matrix. What then corresponds to this type in 

 the living cell? How is the rigidly determinate arrangement 

 of nucleotides in the polynucleic matrix set up? As w^e have 

 seen above, there is a great deal of factual material which 

 indicates that RNA plays a direct part in the synthesis of 

 proteins. Although it is frequently found in the scientific 

 literature, there is less factual evidence for the idea that the 

 specific structure of RNA is in some way determined by the 

 DNA of the nucleus. To use the language now adopted by 

 physicists, the information concentrated in the molecules of 

 DNA is first passed on to the molecules of RNA, after which 

 the synthesis of protein molecules proceeds in accordance 

 w^ith the information which is relayed by the sequence of 

 nucleotides in the RNA chain. ^°® 



However, even if we assume the truth of this hypothesis, 

 it does not carry us much further forward, for the question 

 now arises as to how^ the rigidly determinate arrangement of 

 nucleotides in the DNA was brought into being. 



One can nowadays hardly take the view that DNA does 

 not take part in metabolic activities, does not undergo any 

 changes in the process of development of the cell, but merely 

 reproduces itself in such a way that each new molecule arises 

 directly by autocatalysis from a pre-existing molecule. This 



