29. DEOXYRIBONUCLEIC ACIDS AS MACROMOLECULES 



35 



I > 





7^ 



Fig. 18. DNA, globular particles. 



it seems that heterogeneity can be observed. It is, however, not impossible 

 that degradation had taken place during the preparation of DNA in globu- 

 lar form. 



(c) The molecular wheight of DNA particles is very large, certainly of 

 several million. Light-scattering measurements of the mean molecular 

 weight M w of these particles are open to much criticism on technical 

 grounds and "we do not know to what extent the values found for M w are 

 erroneous. These M w values can be divided into two main groups. In the 

 first, M w lies between 6 and 8 million, in the second it ranges from 12 to 16 

 million. Treatment with chymotrypsin does not change the value of M w in 

 the first group, but it reduces the M w values of the second group to those of 

 the first. 



The use of hydrodynamical methods can also be criticized, because it re- 

 lies on assumptions whose adequacy seems difficult to appreciate. The mo- 

 lecular weight obtained by these methods is of the same order as M w , 

 though somewhat higher. 



(d) Tiie particles of DXA in dilute solution have a linear configuration 

 and the value found for the weight per unit length is quite compatible within 



C. Sadron, Onzierm Conseil <lt <'himi< Solvay, Brussels, 1959. 



