VIRAL FUNCTIONS: ORDER AND DISORDER 



superimposed on the cellular order. As a consequence, the cellular 

 order is perturbed, and the results may be as different as "lysogeny" 

 when bacteria are concerned, or cancer when the mammalian cell 

 is involved. 



Various aspects of viral order, viral functions, and cell/virus 

 interactions will be discussed in this chapter. 



\^iRAL order: the infectious viral particle, or virion. The most 

 general idea of a viral particle can be derived from the study of 

 one of the simplest and smallest viruses. In order to simplify things, 

 to spare words, and to be modern, the infectious viral particle will 

 be called virion, which means a unit of virus, according to recent 

 terminology. 



Protein coat 



Subunit 



Nucleic acid 



Figure 24. Schematic Representation of a Viral Infectious Particle 

 (Virion). 



The genetic material (nucleic acid) is folded and enclosed in a coat or capsid. 

 The capsid is made of subunits, the capsomeres, arranged in an orderly fashion. 



The virus of poliomyelitis, the poliovirus, will be taken as a pro- 

 totype of a virion. This virus has been obtained in a high degree of 

 homogeneity and its chemical constitution established. It has been 

 crystallized and its crystals studied by X-ray diffraction. 



The virion is a polyhedron. It is composed of a protein shell en- 

 closing the nucleic acid (Figure 24). X-ray diffraction shows that 



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