106 CONTROL MECHANISMS IN CELLULAR PROCESSES 



Before the advent of electron microscopy, various basophilic 

 granules of the cytoplasm were called chromidia and that was the 

 name that many European authors adopted for the Palade granules 

 (Monne, 1948; Weber, 1958). Most biochemists were at that time 

 still talking of microsomes, a term which in the history of cytology 

 has also had manv different meanings. When the ribonucleopro- 

 tein nature of these granules was recognized and when they could 

 be isolated from microsomes, the term ribosomes was introduced 

 and, subsequently, widely accepted. 



RNA and Protein Synthesis. Broken cell preparations consisting 

 of microsomes were shown to be able to synthesize proteins (Za- 

 mecnik and Keller, 1954; Borsook, 1956). Later, the purified ribo- 

 somes were found to be the functional part of microsomes. It could 

 be thus demonstrated that ribonucleoproteins are active in protein 

 synthesis and the original ideas of Caspersson ( 1941 ) and Brachet 

 (1942) bore ample fruit. 



The occurrence of protein synthesis in ribosomes could also be 

 demonstrated in a living cell. When Neurospora was fed H^ leucine 

 and centrifuged 5 to 15 seconds later, the radioactivity newly incor- 

 porated into proteins could be found mainly in the ribosome layer 

 of the cell. The mitochondrial fraction also became labeled, but 

 later it could be shown that probably most of this activity was due 

 to ribosomes which filled the spaces between mitochondria (Zalokar, 

 1961). Radioactivity which was found in nuclei could be assigned 

 to the synthetic function of the RNA which is a constant component 

 of the nuclei. 



The search for the chemistry of protein synthesis and the exact 

 function of RNA is one of the most active fields of biochemistry 

 today, and it is not my domain to report it in more detail. Several 

 recent reviews cover the subject ( Brachet, 1957; Chantrenne, 1958; 

 Roberts et al, 1959; Simkin, 1959). 



It is established today that RNA functions in protein synthesis, and 

 it is assumed that it functions as a template. How the amino acids 

 are assembled on this template is not yet quite clear. It was found 

 that the soluble RNA accepts activated amino acids and that there 

 is a specific RNA for each amino acid ( Schweet et al., 1958a; Berg 

 and Ofengand, 1958 ) . Soluble RNA, carrying activated amino acids, 

 is necessary for ribosomes to perform protein synthesis, and it is 

 believed that the soluble RNA serves as an "adaptor" on the ribosome 



