CHAPTER VI 



THE STRUCTURE AND BIOLOGICAL 



FUNCTIONS OF PROTEINS AND 



NUCLEIC ACIDS AND THE 



PROBLEM OF THEIR ORIGIN 



Chemical structure and biological functions 

 of polypeptides and proteins. 



The problem of the primary development of proteins is 

 extremely perplexing, not only on account of its inherent 

 complexity, but also because there is, at present, no agreed 

 definition of the term protein. Many authors of both the 

 nineteenth and twentieth centuries attached a purely chemi- 

 cal meaning to the term while others regarded it as a specifi- 

 cally biological concept. This is reflected in the terminology 

 currently used. In the Russian language the words belok 

 and protein are used synonymously. The Germans generally 

 use the term Eiweissstoff while British and American authors 

 have gone over entirely to the word protein, the older ^vord 

 ' albumen ' having acquired a more specific meaning and 

 being applied only to a particular group of proteins of which 

 egg albumin is one. 



In the beginning the word albumen was only applied to 

 the substance in hens' eggs which forms a ^vhite coagulum 

 when heated. Later on, other substances similar to the white 

 of eggs were included in the term albumen, but this concept 

 was not given any general biological significance in relation 

 to life. On the contrary, it was considered that egg albumen 

 and other analogous substances were no more than the specific 

 products of a few isolated organisms and, in particular, that 

 they were completely absent from plants. Thus, for example, 

 the gluten which had been isolated from flour as early as 

 the end of the eighteenth century was regarded as a curiosity, 

 a freak of nature, and even called matiere vegeto-animale} 

 How^ever, as the study of the chemical substances of living 



229 



