402 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 62 



Figure 1. — The Watson-Crick structure of 

 DNA schematically represented. The paral- 

 lel spiral ribbons represent the paired poly- 

 nucleotide chains. Hydrogen bonding is 

 represented by transverse parallel lines. 

 P=phosphate group, S = sugar unit, A = 

 adenine base, T= thymine base, G=guanine 

 base, C=cytosine base. Arrows indicate 

 that polynucleotide chains run in opposite 

 directions as specified by the sugar-phos- 

 phate linkages. Redrawn form Watson and 

 Crick (1953^. 



