Organization and Replication of DNA in Vivo 



267 



figure 20-3. X ray diffraction photographs of suitably hydrated fibers of DNA, showing the 



so-called B configuration. A. Pattern 

 obtained using the sodium salt of 

 DNA. B. Pattern obtained using the 

 lithium salt of DNA. This pattern 

 permits a most thorough analysis of 

 DNA . ( Courtesy of Biophysics Re- 

 search Unit. Medical Research Coun- 

 cil. King's College. London.) 







♦ * ♦ < 



figure 20-4. The Watson-Crick dou- 

 ble-stranded helix configuration of 

 DNA. 



