Virus

 Viruses:

     Meaning:

       Virus word is derived from Latin word "VENOM" means "POISON'.

    Discovery:

       The first evidence about virus came when in 1884 Charles Chamberland,who worked with Louis Pasteur,found that the causative agents of rabies could pass through the porcelain filter (pore size 100-1000nm).

Tobacco mosaic disease was thought to be caused by bacteria. Iwanosky (1892) extracted the juice from the leaves of tobacco having tobacco mosaic disease.In order to remove the bacteria the juice was pass through porcelain filter .He rubbed the filtered juice on the leaves of healthy plants,expecting no disease to develop but still the healthy leaves showed the disease so because of this he called them filterable agents.

 1n 1900,similar disease producing substance has been seen in both Animls and plants.They named it filterable viruses.

W.M.STANLEY in 1935 prepared the extract of tobacco mosaic virus and purified it after many successful attempts.Under Microscope viruses appeared as silvery crystals.within short time it was shown that silvery crystals made up of nucleoproteins and virus structure was shown as rod type.

   Definition:

      Viruses are small biological entities only seen through Electron microscope are made up of small macromolecules.

  Status of virus:

  Virus lies on border line between living and non living things.

  Living properties of viruses:

1-Viruses are characterized as living because they possess DNA or RNA.

2-They have ability of reproduction.

3-They can undergo mutation and genetic recombination.

4-They have the ability to infect living organisms and show irritability.

5-They get destroyed by UV rays.

  Non living properties of viruses:

1-They are sub-cellular or non-cellular structure.

2-They do not respire,excrete,can be crystallized and stored in much the same way as chemicals.

3-They lack metabolic system.

4-They lack coenzyme and proper enzymatic system.

Classification of viruses on basis of morpholgy and host:

  On basis of morphology viruses are classified into three types;

1)Spherical viruses e.g: Polio etc.

2)Tadpole shape virus e.g:Bacteriophage.

3)Rod shape viruses e.g:Tobacco mosaic virus.

On basis of host they infect viruses are of three types;

1)Animal viruses:

  They are parasites on animals and human beings and cause diseases in them.

  Common diseases in man are polio,small pox,measles,mumps and influenza etc.

  Most animal viruses contain as RNA as genetic material.

2)Plant viruses:

  These viruses cause diseases in plants.

  There are about 2000 plants diseases caused by viruses.

3)Bacteriophage virus:

 This type of virus attacks on bacteria.

 It is a DNA virus with a polyhedral head and tail.

Important mcqs in this topic:

1)Virus is made up _molecule?

Answer: NUCLEOPROTEIN

2)Virus contain _genetic material?

Answer: DNA or RNA

3)Virus stored as chemical ,It is living or non living property of virus?

Answer: Non living

4)Virus was first time purified and studied  by _?

Answer: W.M STANLEY IN 1935

5)Which type of virus attacks on bacteria?

Answer: BACTERIOPHAGE

6)Viruses are _structure?

Answer: SUB CELLULAR OR NON CELLULAR

7)On basis of morphology viruses are classified into _typpes?

Answer: 3

8)Animal viruses are _shape?

Answer: Circular/round

9)Which type of virus is rod shape?

Answer: Tobacco mosaic virus(plants)

10)Virus replication time is _?

Answer: 70 seconds

11)Study of viruses is called?

Answer: VIROLOGY

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