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Thursday, December 02, 2004

Characterization of Viruses

I) Introduction
A virus is a miniscule, acellular, infectious agent having one or several pieces of nucleic acid, either DNA or RNA, but never both.
Pasteur first defined them as a "living thing smaller than bacteria" and termed them virus- Latin for poison.
In 1884 the first vaccine for rabies was developed. Rabies is 100% fatal without this vaccine.
In 1898, viral studies intensified as foot/mouth disease was discovered and was found to be non-cellular.
In the 1950's the study of virology emerged as a science.
_B) Virus Terminology

  • Non-living agent with either DNA or RNA but never both
  • Nucleic acid is surrounded by a protein coat called a capsid
  • The shape is determined by the capsid
  • They are associated with all life forms- all organisms contain viruses
  • Usual ranges in size is 1/100 to 1/1,000 of the size of a host cell
  • Viruses have an extracellular state, called a viroin, consisting of a protein coat called the capsid.
  • They lack a cytoplasmic membrane and have no cytosol.
  • An envelope can be on selected virus types and is made of a lipid bilayer over the capsid

_C) Virus Types

  • Naked-- lacks an envelope and is hardest to control
  • Enveloped--easier to kill and normally infects humans
  • There are two states of a virus. (1) Chemically inert being outside of the host, and (2) Viroin state- replicating within a host.

Isohedral shape -- Official page

Helical shape, usually infectious of plants and animals (example from tobacco mosaic virus)

Bacteriophage, infects bacteria Official page

Viral envelope (example from herpesvirus family)

Naked vs. Enveloped


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