196 THE PHYSICS OF VIRUSES 



fected plant cells. The nucleic acid is ribose nucleic acid and it is 

 bound relatively tightly to protein, although this is not charac- 

 teristic of all plant viruses, and TMV is an exception. It is con- 

 siderably radiation sensitive, and so is probably very simjjle and 

 functional in structure. It has a high proportion of internal water 

 of hydration. 



In the representation, the nucleic acid has been divided rather 

 arbitrarily into two parts, one at the center which is supposedly 

 primarily involved in the self-duplication process, and one 



D 



Nucleic Acid 



Protein 



Water 



TMV 



Fig. 8.3. End view of tobacco mosaic virus. Again, the location of the nucleic 

 acid is speculative. The repeated small antigenic pattern is shown, with 

 oriented, aromatic amino acids forming a part of each antigen. 



attached firmly on both sides to protein and having the antigenic 

 characteristic under its control in consequence. It has also been 

 assumed that a relatively small number of surface molecules are 

 concerned with enzymatic digestion of the surface of the plant 

 cell. These are shown separately. The two antigens are indicated 

 by making the small one a substructure in the large. 



In the next figure, the end view of tobacco mosaic virus is 

 shown. The long hexagonal rod shape has already been shown 

 in Fig. 2,13, so only the end is shown here. There are really only 

 two features which need comment. The first is the fact that 6% 

 of the virus is nucleic acid, which rather readily separates from 



