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Virion structure

The virion contains only a single type of nucleic acid, which can be either ds or ss DNA or RNA. This genome is encased by a protein coat called a capsid. This capsid protects the genome by forming an impermeable barrier. It is composed of multiple copies of a single protein (two kinds in more complex viruses). Some animal viruses have a lipid membrane around the capsid, and these are called enveloped viruses. Viruses without this lipid membrane are called naked viruses. There are two capsid shapes:

  • Icosahedrons
  • Helix

To summarize:

  • Nucleic acid is either RNA or DNA.
  • Multiple proteins form a capsid to protect nucleic acid.
  • Capsids either icosohedral or helical in structure.
  • Some viruses are naked; others have an envelope.

There have been 2 important advances in visualization of viruses:

  • Electron microscopy
  • Plaque assay
    • Add dilute suspension containing virus to lawn of susceptible host cells.
    • After infection, cover layer of cells with agar.
    • Incubate.
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