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Structure of Viruses 



I. Introduction 



In the border zone between living cells and separate molecules, there is 

 a class of particles having some characteristics of living cells and some 

 characteristics of separate molecules. These are called viruses. For 

 historical reasons, viruses infecting bacteria are given the separate name 

 bacteriophages, or just phages for short. All viruses — plant, animal, and 

 bacteriophages — have many common properties. These include ex- 

 tremely small size, 10-400 m/x; chemical simplicity (few types of 

 molecules); lack of metabolism or reproduction outside of living cells; 

 ability to attack only very specific cell types ; absence of typical cellular 

 structures such as membrane, nucleus, and granules; and ability to 

 reproduce inside of the cell attacked, eventually destroying the host cell. 

 Virus studies have appealed to persons wishing to apply physics and 

 chemistry to biology for a number of different reasons. First and fore- 

 most, no doubt, is the fact that viruses are simpler and exhibit a greater 

 regularity than any single-celled plant or animal. At the same time, 

 virus particles do reproduce and mutate in a fashion quite analogous to 

 the more complex living organisms of a cellular nature. Another major 

 reason biophysicists have been interested in virus research is that com- 

 plex physical tools are necessary to study viruses ; techniques used include 



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