Pyrimidine Moieties in Animals, Plants, and Bacteria 109 



This paradox appears to have been resolved by the hypothesis 

 that ribosomal-RNA is not the intermediate carrier of information 

 from gene to protein, but rather that ribosomes are non-specialized 

 structures wliicii receive genetic information from the genes in 

 the form of an unstable intermediate or messenger (4). Although this 

 radical revision in concepts was introduced as recently as May, 

 1961, an impressive array of supporting evidence has now been 

 amassed. This evidence will be discussed briefly in this section. 

 A schematic representation of the mechanism of information 

 transfer between DNA and informational-RNA (messenger-RNA) 

 is shown in Figure 8. 



DNA DOUBLE HELIX 









NEW RNA CHAIN 



Fig. 8. Hypothetical representation of the transcription of genetic information 

 from the DNA double heUx to "Informational-RNA." 



It is assumed that DNA can act as a template for the syn- 

 thesis of a new messenger-RNA chain. The mechanism is not 

 unlike tliat by which the DNA chains are replicated. Probably, 

 the DNA double helix partially unwinds. Each base then attracts 

 a complementary free ribonucleotide already available for poly- 

 merization within the cell. The free ribonucleotides, whose phos- 

 phate groups already possess the free energy necessary for poly- 

 esterification, then link up with one another, after being held in 

 place by the DNA template chains, to form a new ribopoly- 

 nucleotide molecule. Thus, DNA serves as a template for the 

 synthesis of a complementary RNA strand. The newly formed 



