VIRUS GENETICS, MULTIPLICATION, AND PHYSICS 



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which means there is a small attraction between the particles. 

 This is not significant because thermal agitation is sufficient to 

 prevent any important binding between virus j)articles at this 

 range of separation. As the distance apart becomes less, there 



Fig. 8.9. Potential energy between two southern bean mcsaic virus particles. 

 The double-layer repulsion and the Van der Waals attraction produce a 

 potential barrier. This varies in character with ionic strength, and may be a 

 factor in keeping constituents together during growth and then forcing them 

 apart at division. 



is a sharp increase in the mutual potential energy, which means 

 a quite definite repulsive force in this region. At a distance of 

 about 6 A, the Van der Waals attraction makes up for the 

 double-lav^er repulsion, so that within a range of 6 A there is 

 quite strong binding between the two particles. 



