FRITZ LIPMANN 



part the previous success of the methodology of cleavage into 

 the smallest possible units which now acts almost like a mental 

 block. 



The common denominator in many of our difficulties seems 

 our inability to understand structure in biochemical terms. 

 This is particularly evident in the approach to protein synthesis. 

 With the analysis of protein synthesis, the energy problem now 

 tangibly merges with the propagation problem. This is ob- 

 vious if one realizes that many forms of specificity are an ex- 

 pression of a particular sequential arrangement of the amino 

 acids, a sequential arrangement into chains of various shapes, 

 together with an interlocking through interchain links such as, 

 e.g., disulfide links. 



A lively discussion of the manner in which these sequences 

 are built up has recently sprung up, motivated in particular 

 through ingenious models for deoxynucleic acids (23). These 

 nucleic acids appear to carry a directing force, often referred to 

 as the code of replication. Metabolically speaking, there is 

 still a link missing from predetermined nucleic acid chain se- 

 quences leading to determination of amino acid chain sequences, 

 although dependence of protein synthesis on nucleic acid struc- 

 tures appears to be quite real. In spite of still meager facts, 

 there is a need to start discussion in this biochemical vacuum. 



Before embarking on particulars, it seems important to 

 realize that the synthesis of a fixed sequence can be effected 

 methodologically either by a predominant space pattern, a 

 template, or by a timing device analogous to the assembly line. 

 In reality, it most likely will be effected by a mixture of both. 

 It is my impression that presently template processes have been 

 in the foreground of discussions, including my own (16), because 

 of the greater ease in devising template models. The assembly 

 line procedure, however, is really met with mostly in biochemical 

 systems, including a few cases with sequential arrangement on a 

 relatively small scale (10,21). 



These problems are now in the foreground because it is here 

 that genetics and biochemistry meet, namely, where the trans- 



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