BIOSYNTHESIS OF PROTEINS 



265 



tion of amino acids, while synthetic phosphorylated amino 

 acids which are artificially introduced into an organism do 

 not enter directly into the synthesis of proteins. It must 

 therefore be admitted that the actual mechanism of the 

 transfer of energy during the synthesis of proteins is still not 

 quite clear. H. Borsook"^ considers that there first occurs 

 the activation of the carboxyl groups of free amino acids by 

 ATP, either directly or through coenzyme A. Afterwards 

 the activated amino acids combine with nucleic acid accord- 

 ing to the following scheme : 



base 



base 



base 



base 



sugar sugar [e — co — chRi — NHg 



/I / 1 / 



o o o o + i + 



1/1/ 



0=P 0=P ^E — CO — CHRg — NH2' 



OH 



OH 



sugar 



/ I 



o o 



I / 



o=p 



I 



o 



sugar 



I / 

 o o 



1/ 



0=P + 2EH 



I 

 O 



0=G — CHNH2 0=C — CHNH2 

 / / 



Ri 



Peptide bonds are then created, after which the finished 

 protein molecule is liberated from the nucleic acid. 



On the other hand, according to S. E. Bresler,^^^ energy 

 is necessary for the last stage of the process, the desorption 

 of the polypeptide chain from the surface of the polynucleo- 

 tide. According to this author, the biosynthesis of proteins is 

 based on the chemosorption of amino acids on the energy- 

 bearing phosphorylated gioups of ribonucleic acid. Under 

 the conditions of the adsorbed layer the equilibrium is 

 shifted towards synthesis. The action of proteolytic enzymes 

 will therefore lead to the joining together of amino acids 

 and the synthesis of protein molecules, which does not 

 require the additional expenditure of energy. Energy is 

 required for desorption of the finished protein molecule and 

 this is derived from high-energy bonds in the phosphorylated 

 nucleic acid. The surface which has been freed from the 

 protein is again phosphorylated and the cycle repeats itself. 



