CHAPTER 2 



Structure and Function of Nucleic Acids as 

 Cell Constituents'^ 



It is safe to say that living systems require the presence of both 

 types of nucleic acid or, in the case of parasitic systems, the 

 presence of at least one. If, to use a designation of Schr6dinger\ 

 one refers to the chromosomes as "the hereditary code-script", 

 the great biological importance of all components of these nuclear 

 structures, viz., nucleic acids, proteins, and, perhaps, lipids, is 

 obvious, unless one assumes that one or the other of these com- 

 ponents has been added by nature as a meaningless and purely 

 decorative flourish. This is, however, not likely. 



In animals and higher plants the deoxypentose nucleic acids 

 (DNA) are exclusively or almost exclusively situated in the 

 nucleus. Pentose nucleic acids (PNA) are present in the nucleoli 

 and the various cytoplasmic elements, e.g., the mitochondria, 

 submicroscopic particles, etc. Recent work with Elson^ on the 

 nucleotide composition of PNA in different fractions of rat liver 

 cells has provided preUminary evidence of differences in com- 

 position between nuclear and cytoplasmic PNA. It is not yet 

 known whether this will be generally true; but results, recently 

 reported by Magasanik^, seem to point to the presence in pig 

 liver PNA of two differently composed fractions. 



Whether DNA really is hmitedto the nucleus is not entirely 

 certain, since the available cytochemical or cytophysical methods 

 presumably require the presence of a compact mass of DNA 

 and may not reveal its occurrence in a diffusely distributed form, 

 as could be the case in the cytoplasm of egg cells (c/. Ref. 4). 



* Reprinted with permission from Federation Proc, 10 (1951) 654-659. 

 References p. 37 



