56 Nature of the Genetic Material 



c. General conclusions 



In summarizing what is known about the location and nature of 

 the genie material in the chromosomes, we must keep in mind that the 

 nucleus not only has genetic functions but also controls the physi- 

 ological activity of the cell in an exchange of materials. If we find, 

 therefore, chemical differences in protein content between nuclei of 

 differently functioning cells, we cannot draw conclusions in regard to 

 the genie material. 



The biochemists at present are in favor of the idea that DNA is 

 the genie material in the chromosomes. In favor of this view are ( 1 ) 

 the constancy of the amount of DNA in all cells of a species, whereas 

 the protein contents of the chromosomes vary; (2) the location of 

 concentrations of DNA at points of the chromosome which the experi- 

 ment reveals to be genie (the bands in the salivary gland chromo- 

 somes); (3) the facts of bacterial transformation via specific DNA 

 and transduction via phage; (4) the role of the nucleic acids in 

 viruses; (5) the structure of the DNA molecule which permits 

 visualizing self-duplication. 



But it must be reahzed that many of the detailed features of 

 chromosomal behavior and structure fit better into the opinion of some 

 chemists and many geneticists that the nucleic acids are needed as 

 templates of protein synthesis, or as scaffolding to keep the duplicat- 

 ing protein molecules in position ( Haurowitz, 1950 ) . It is, furthermore, 

 so much more probable that the genie functions are based upon an 

 enzymatic nature of the genie material, and enzymes are proteins. A 

 powerful argument against the genie nature of DNA can be derived 

 from the group of facts which show that DNA prepared and some- 

 times mass-fabricated in certain nuclei (nurse cells, tapetum cells, 

 and nurse cells and sperm phagocyted by oocytes) can be transferred 

 to the cytoplasm of an egg cell where it may be used directly in 

 building up the DNA of the embryonic nuclei, and, in addition, may 

 probably be used in cytoplasmic protein synthesis as well. The 

 negative fact that no quantitative constancy has been found for any 

 nuclear constituent but DNA should be used with caution, because 

 the optical methods based upon the Feulgen reaction allow such 

 measurements for DNA; while a comparative direct method for the 

 intact protein in the chromosome does not exist. If DNA is the scaf- 

 folding for protein synthesis, its constancy is to be expected. 



We conclude that a final decision has not been reached and that 

 it cannot be stated as a dogma or as a proved fact that DNA is the 



