IX. METABOLISM 291 



pigions and rats, and found appreciable amount of N^^ in the RNA, 

 subsequently isolated from the livers, but only negligible amount in 

 the DNA. It has thus been generally ascertained that at least RNA 

 is metabolically much active than DNA. Griffm et al. (120) have' 

 even concluded that DNA is entirely inert. 



The nucleic acid existing in the gene which always requires the 

 most strong pattern appears to be DNA, whereas as pointed out 

 already DNA is much more stable than RNA. It may be said, there- 

 fore, that DNA is fit for the establishment of strong pattern but unfit 

 for the action as an energy donor for which some brittleness should 

 be required. On the contrary, RNA is suitable for the purpose of 

 providing energy owing to its brittleness although inferior to 

 DNA in the action of pattern formation, so that while DNA is present 

 in nucleus to provide the strong pattern, RNA exists in cytoplasm to 

 deliver the pattern directed by the gene to proteins to be synthesized 

 and also to provide the energy required for the synthesis. .SchSnhei- 

 mer (121) has shown that proteins are continuously being synthesized 

 and hydrolysed so that it is quite possible that part of the energy for 

 synthesis of proteins is obtained from the hydrolysis of other proteins 

 or peptides. Such proteins may possibly be nucleoproteins containing 

 RNA. 



As already considered, in case of protein synthesis, component 

 amino acids are to be adsorbed onto the template, which is probably 

 involved in cytoplasmic particles containing RNA in rich amount, in 

 adapting themselves to the specific pattern of the template, but since 

 they have both amino and carboxylic groups in a free state prior to 

 condensation into polypeptide chain, they may exert a disturbing 

 effect upon the template. This disturbing effect may lead to the 

 partial decomposition of RNA with the liberation of the high energy 

 phosphate bond. Meanwhile, amino acids adsorbed may also be 

 disturbed in their structure and as a result they are activated to be 

 readily united into a polypeptide chain. 



It has been shown by using various isotopes that proteins com- 

 posing animal tissues are constantly being renewed in a considerable 

 speed. For example, liver tissue rapidly takes up amino acids follow- 

 ing the injection or feeding, and the time for half replacement of the 

 liver protein in the rat has been estimated to be about 7 days (122). 

 Such a rapid renewal of tissue protein may partially be dependent 

 upon the decomposition of the nucleoprotein as above mentioned, but 

 there may be another important reason for the renewal. Since all the 

 life phenomena involve the structural alteration of the protoplasm, 

 the pattern of the protoplasm may be more or less deformed during 

 the life process. As was mentioned earlier, the pattern thus deformed 



