Viruses

Viruses are non-living particles made of genetic material (DNA or RNA) surrounded by a protein coat.They are about 0.02 to 0.3 micrometres (20 to 300nm) in diameter.Viruses enter living cells where the host cell replicates the viral genetic material and the cell's biochemistry and resources are used to make more virus.Viruses reproduce rapidly and evolve quickly by mutation and natural selection by developing adaptations to the host and host immune system. Most viruses are pathogens.Viruses cause diseases in every type of organism including bacteria. Bacteriophages are viruses that take over bacterial cells to produce more viruses, destroying the bacterial cells in the process.Bacteriophages are used by scientists to identify and treat some diseases.