Viruses and viroids

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Viruses

Non living  :- 

  • No components of cell 
  • No cell membrane 
  • Inert 
  • No metabolism
  • No reproduction on its own 

Living :-

  • Inert only outside a living host
  • Possess genetic material (DNA/RNA )
  • They can reproduce / mutate when inside a living host

Viruses 

  • Acellular
  • Extremely small
  • "Virus" term is given by ivanowsky
  • Inert outside a host
  • Obligate parasite
They are those parasites that cannot complete its life cycle without exploiting a suitable host 

Structure :
  • It is a nucleoprotein
  • It contains a protein, genetic material in the form of RNA/DNA
  • It has a protein coat :-capsid ensures protection of nucleic acid
  • Capsid contains helical arrangement of capsomeres 
Plant viruses :- single strand of RNA 
Animal viruses :- double strand of RNA/DNA 
Bacterial viruses :-Bacteriophages (double strand of DNA )


Diseases :-AIDS , Small pox , Mumps , Influenza, Dwarfing in plants, Mosaic formation in plants 

Viroids

  • Viroids means virus like 
  • They are smaller than viruses
  • Infectious agents like viruses 
  • They are composed of free RNA 
  • protein coat is absent in them

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