Acellular organism - Virus viroids and Prions

• There are so many structure which are non cellular or acellular.

• They exist their presence around the cellular organism. They have some significant impact on living organism.

Virus 

• A   Virus is non cellular organism that have a crystalline structure outside the living cell. 

• Once it come with contact of living cell than it uses the system of host cell and start to replicate with in host cell.

Remember 👌👌Acellular organism like virus, Virioids and Prions are not  getting any place in any Classification.

• Term virus has been taken from the word "Venom" by the Louis Pasteur. 

• Dmitri Ivanowsky in 1992 identified some disease causing particle from Tobacco mosaic disease. 

• These particles are smaller than bacteria because they can pass bacteria proof filters.

• M.W. Beijerineck extracted the some fluid from plant affected  by Tobacco Mosaic disease. This infected fluid was renamed by "Contagium Vivum Fluidium" 

• W.M. Stanley crystalised the virus particle and these Crystal are made up of protein. 

• Virus is non living outside the living cell and behaves like obligate parasite.

• Virus has a protein coat and its infectious genetic material is enclosed inside the protein cost. 

• The protein coat is called capsid which is made up of small subunit called capsomere. 

• Capsomeres are arranged helically or polyhedral geometric form.

• The genetic material or nucleic acid inside the protein is either DNA or RNA which contain nucleoprotein.

• Since virus has no ribosome , mitochondria or other cell organs hence virus is fully depend on cellular machinery on host for replication or protein synthesis.

• Virus with genetic material single stranded RNA infect the plants. 

• Mosaic formation, leaf curling or rolling, yellowing and vein clearing, dwarfism  stunded growth are symptoms of virus infection.

• Virus with genetic material single stranded or double stranded RNA and double stranded DNA  infect the animals. 

• Mumps, small pox, herpes influenza are vital disease.

Viroids - 

• T. O. Dienier discovered a new infectious agent in spindle tuber disease of potato. 

• This agents is smaller than virus. It is devoid of protein coat but has free infectious RNA. Its RNA has low molecular weight.

Prions - 

• It has been found that certain neurological infectious disease is transmitted by folded protein. 

• These infectious protein is called Prions. The size of prions are similar to virus. 

• Bovine Spongiform encephalopathy or mad cow disease in cattle is caused by Prions. Cr Jacob disease in human is also caused by the its variants.