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



Figure 4. This figure is diagrammatic. The two ribbons symboHze the two 

 phosphate-sugar chains and the horizontal rods the pairs of bases holding the 

 chain together. The vertical line marks the fiber axis, 



pattern. To fit these observations our structure has a nucleotide on each chain 

 every 3.4 A in the fiber direction, and makes one complete turn after 10 such 

 intervals, i.e., after 34 A. Our structure is a well-defined one and all bond dis- 

 tances and angles, including van der Waal distances, are stereochemically accept- 

 able. 



198 



