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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)
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"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. |
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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. |
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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). |
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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. |
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