J. D. WATSON AND F. H. C. CRICK 



D.N. A. 



BASE SUGAR 



\ 



PHOSPHATE 



BASE SUGAR 



\ 



PHOSPHATE 



/ 



BASE SUGAR 



\ 



PHOSPHATE 



/ 



BASE SUGAR 



\ 



PHOSPHATE 



/ 



BASE SUGAR 



\ 



PHOSPHATE 



Figure 1. Chemical formula (diagrammatic) of a single chain of desox3Tibonu- 

 cleic acid. 



It should be noted that the chain is unbranched, a consequence of the regular 

 internucleotide linkage. On the other hand the sequence of the different nucleo- 

 tides is, as far as can be ascertained, completely irregular. Thus, DNA has some 

 features which are regular, and some which are irregular. 



A similar conception of the DNA molecule as a long thin fiber is obtained from 

 physico-chemical analysis involving sedimentation, diffusion, light scattering, 



194 



