Write about the discovery and structual organization of viruses .

Explanation

In 1982 , the Russian Pathologist Dmitri Iwanowski ,while studying Tobacco mosaic disease , he filtered the sap of diseased tobacco leaf through filters and is injeted into a healthy plant . He found th symptoms of Mosaic disease in it . Finally he reportes that , a filetrable agent was responsible for the disease .Later martinus Beijerinck repeated Iwanowski.s experiments and concluded that m the disease causing agent was a .cantagious living fluid . (cantagium vivium fludium ) . V. Stanley (1935) purified the sap and announced that the virus causing mosaic diseases in tobacco could be crytailized and was named TMV. Franlanke conreal (1956) confirmed that the genetic material of TMV is RNA.
Structure :- Viruses range in size from 300 nm as in TMV to 20 as in Paroviruses .All viruses consist of two basic components ,a core of nucleic acid that forms the genome and the surrounding coat of protein known as capsid . The capsidgives shape to the virus and provides a protective covering for the genome. It is made up of protein sub - units called capsomeres. A virus contains its genetic information in either a double stranded (ds) DNA or single stranded (ss) DNA.In general ,phytophage have ss RNA and zoophages hav ds DNA. bacteriophages are usually ds DNA viruses .
Shape :-
(a) Helical viruses resemble long rods .
Eg : Rabies Virues Tobacco Masaic Virus .
(b) Polyhedral viruses . They resemble polyhedral shape (many sided )
Eg: Herpes simplex and polio viruses .
(c ) Enveloped viruses : -
The capsid is covered by an envelope which are roughly spherical .
Rg : Influenz virus .
(d) Complex viruses :- Viruses which infect bacteria have complicated structures .
Eg : Bacteriophages have polyhedrial symmetry in the head and helical symmetry in the tall sheath .