VIRUS

Virus literally means ‘poison’. They are also called as filterable molecules during olden days as they are able to pass through filter pores which do not permit bacteria to pass. They are the submicroscopic entities. Andre Luoff, a virologist and Nobel Laureate, defined the viruses as “Viruses are Viruses”.
The general characteristics of Viruses are :
1. Viruses are a cellular organisms that are infectious in nature.
2. They are 10 to 100 times smaller than most bacteria and range from 20 to 200nm size.
3. They exist in two states namely extra cellular and intracellular.
4. They are obligate intracellular parasites
5. Viruses are incapable of independent growth in artificial media. They lack metabolic machinery of their own to generate energy or to synthesize proteins. Viruses depend on host cell machinery to carry out vital metabolic functions. However, they consist some genetic information for reproduction.
6. They reproduce only in living host cells such as plants, animals and microorganisms.
7. They structurally complete nature and infectious virus is called viron.
8. They possess either DNA or RNA as genetic material but never both.
9. The nucleic acid can be either single stranded or double stranded.
10. Genetic material is enclosed in a highly specialized protein coat called capsid.
11. The capsid may be naked or enveloped.
12. Some viruses such as bacteriophases possess a banal structure of head and tail attached.
13. They are neither prokaryotic or eukaryotic. They do not consist cytoplasm and cytoplasmic organelles.
14. Several viruses cause different diseases in plants, animals and human beings.