Expansion of virus

1.	Expansion of virus
Answer» \tViruses did not find a place in classification since they are not truly ‘living’.\tThe viruses are non-cellular organisms that are characterised by having an inert crystalline structure outside the living cell.\tOnce they infect a cell they take over the machinery of the host cell to replicate themselves, killing the host.\tVirus means venom or poisonous fluid, this name was given by Pasteur. D.J. Ivanowsky (1892).\tM.W. Beijerinek (1898) demonstrated that the extract of the infected plants of tobacco could cause infection in healthy plants and called the fluid as Contagium vivum fluidum (infectious living fluid).\tW.M. Stanley (1935) showed that viruses could be crystallised and crystals consist largely of proteins.\tViruses are nucleoproteins containing a nucleic acid (RNA/DNA) may be single stranded or double stranded surrounded by a protein coat called capsid made up of smaller units called capsomeres which are arranged in helical forms.

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