O " 



C in phosphate 

 -ester chain 



C & N in bases 



FIGURE 1 .2b. Drawing of the DNA molecule in which solid circles illustrate atoms. 

 There are two helical grooves of unequal size on the outside of the DNA molecule 

 (after Feughelman, Langridge, Seeds, Stokes, Wilson, Hooper, Wilkins, Barclay, and 

 Hamilton, 1955, Nature, 175:834). 



11 



