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Gamma phage, an example of a virus.
Virology

Virology is the study of viruses such as the cold virus.

Virologists are responsible for many immunisations against common viruses like the common influenza (Flu) and things like chickenpox and smallpox.

DNA Viruses

DNA viruses use DNA for their genome. An example of a DNA virus is Herpes simplex. Viruses that are not DNA viruses use RNA for their genome and are called RNA viruses.

RNA Viruses

RNA viruses are viruses that use RNA as their genetic material. In humans, well-known RNA viruses are those that cause SARS, Influenza or Hepatitis C.

Viruses that are not RNA viruses use DNA for their genome and are called DNA viruses.

Viruses have a classification system, invented by David Baltimore, a Nobel Prize winner. The RNA viruses in the Baltimore system are classified as:
  • IV: (+)ssRNA viruses (+ strand or sense) RNA (e.g. Picornaviruses, Togaviruses)
  • V: (−)ssRNA viruses (− strand or antisense) RNA (e.g. Orthomyxoviruses, Rhabdoviruses)
  • VI: ssRNA-RT viruses (+ strand or sense) RNA with DNA intermediate in life-cycle (e.g. Retroviruses)
"Sense" in RNA means "ready to make proteins, as messenger RNA does".

"Antisense" in RNA means "complementary to messenger RNA". In complete complementarity each nucleotide is across from its opposite number, so antisense RNA can produce sense RNA.

Another system is run by the International Committee on Taxonomy of Viruses (ICTV). It uses terms from the familiar Linnaean taxonomy, like orders and families.
Mutation rates

RNA viruses have very high mutation rates compared to DNA viruses. This is because viral RNA polymerases lack the proof-reading ability of DNA polymerases. This explains why it is difficult to make effective vaccines to prevent diseases caused by RNA viruses.

Some genes of RNA virus are important to the viral replication cycles and mutations are not tolerated. For example, the bit of the hepatitis C virus genome which encodes the core protein is highly conserved, because it is essential to start translation.
Coronavirus

Coronaviruses are viruses in the family Coronaviridae. They are enveloped viruses with a positive-sense RNA genome. They have a nucleocapsid of helical symmetry. The genome size of coronaviruses are about 26 to 32 kilobases, extraordinarily large for an RNA virus.

The name "coronavirus" is derived from the Latin corona, meaning crown or halo, and refers to how virions look under electron microscopy (E.M.). They have a fringe of large, bulbous surface projections looking like a crown. This morphology is created by the viral spike (S) peplomers, which are proteins on the surface of the virus. They decide which cells the virus can infect.

Proteins that contribute to the structure of coronaviruses are the spike (S), envelope (E), membrane (M) and nucleocapsid (N).
Diseases

Coronaviruses infect the upper respiratory and gastrointestinal tracts of mammals and birds. Six different strains of coronaviruses infect humans.

Coronaviruses are believed to cause many common colds in human adults. The significance and economic impact of coronaviruses is hard to assess. Unlike rhinoviruses (another common cold virus), human coronaviruses are difficult to grow in the laboratory.
Kiddle: Virology
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