Current Views in Science

Although isolated virus particles are just assemblages of chemicals, they consists of chemical substances of a very special kind - the proteins and nucleic acids that are the essential constituents of living matter. In viruses these substances can be studied in isolation, and it was such studies that led molecular biologists to some of their greatest discoveries in the 1950s and 1960s. Nucleic acids are chainlike macro-molecules that carry information for self-replication and protein synthesis. When a virus enters a living cell it is able to use the cell's biochemical machinery to build new virus particles according to the instructions encoded in its DNA or RNA. A virus, therefore, is not an ordinary parasite which takes nourishment from its host to live and reproduce itself. Being essentially a chemical message, it does not provide its own metabolism, nor can it perform many other functions characteristic of living organisms. Its only function is to take over the cell's replication machinery and use it to replicate new virus particles. This activity takes place at a frantic rate. Within an hour an infected cell can produce thousands of new viruses and in many cases the cell will be destroyed in the process. Since so many virus particles are produced by a single cell, a virus infection of a multicelled organism can rapidly destroy a great number of cells and thus lead to disease. Although the structure and functioning of viruses is now well known, their basic nature still remains intriguing. Outside living cells a virus particle cannot be called a living organism; inside a cell it forms a living system together with the cell, but one of a very spcial kind. It is self-organising, but the purpose of its organization is not the stability and survival of the entire virus-cell system. Its only aim is the production of new viruses that will then go on to form living systems of this peculiar kind in the environments provided by other cells.
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