40 The Chemistry of the Injured Cell 



c. But the genetic control is ultimately exerted by DNA. Neverthe- 

 less, there is sound evidence that protein synthesis can occur even 

 in the absence of DNA. Indeed, interference with DNA synthesis 

 does not, in general, affect the synthesis of protein or of RNA 

 (Chantrenne, 1958; Fincham, 1959) . Though many biochemists 

 like the idea that DNA exerts its control on protein synthesis by 

 passing information on to RNA which then controls protein synthe- 

 sis directly, the view is not accepted by all and much more work is 

 needed to establish the hypothesis. Taking everything into con- 

 sideration, it seems certain that RNA is concerned in at least two 

 distinct ways in protein building, (a) through SRNA, as we have 

 seen, it is involved in the transport of activated amino acid residues 

 to the site of protein synthesis, and (b) through ribonucleoprotein, 

 it is involved at the site of synthesis (Simkin 1959), What- 

 ever may be the intermediate stages there is no doubt that RNA 

 must be present at the site of synthesis and it is generally assumed 

 that this RNA assists in the linkage of amino acid residues to form 

 polymers and in particular in determining the sequence of amino 

 acid residues in the polypeptide chains so formed. We have no 

 direct information about the mechanisms involved although many 

 ingenious suggestions have been offered. Crick (1958) , for instance, 

 thinks that SRNA might provide the activated amino acid with an 

 "adaptor" molecule, the adaptor then playing some part in con- 

 trolling the way in which the amino acids are polymerised together 

 in the correct sequence. Hoagland suggests that the whole of the 

 SRNA molecule might serve as an adaptor. Crick rather fancies a 

 nucleotide. In any case, the existence of a "template" appears to be 

 necessary for polymerisation to form a polypeptide chain (Fincham). 



PROTEIN DISTURBANCES IN THE DAMAGED CELL 



We are on even more shaky ground in assembling facts about 

 protein disturbances in the damaged cell than we were in discussing 

 protein metabolism in the normal cell. Clearly, the most that we 

 can do is to put before the reader such information as we possess at 

 present, knowing full well that much of what we write may be 

 superseded before very long. 



