|Transmission electron micrograph of Avian coronavirus|
|Illustration of a SARS-CoV-2 virionspike proteins (S) Red: lipid bilayer envelope Grey: Yellow: envelope proteins (E)membrane proteins (M) Orange:|
Coronaviruses are a group of RNA viruses. They cause diseases in birds and mammals, including humans. These diseases can be mild, or they can be fatal. In humans and birds, they cause respiratory tract infections. Mild illnesses in humans include some cases of the common cold (which is also caused by other viruses, for example rhinoviruses). More lethal varieties can cause SARS, MERS, and COVID-19.
They are enveloped viruses with a positive-sense RNA genome. The genome size of coronaviruses is about 26 to 32 kilobases, which is extraordinarily large for an RNA virus. There are four major groups of coronaviruses, called alpha, beta, gamma and delta.
The most famous coronavirus is one of the betas, the kind that causes Coronavirus disease 2019 in humans.
The name "coronavirus" comes from the Latin word corona, meaning "crown" or "halo", and refers to how virions look under an 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 of coronaviruses are the spike (S), envelope (E), membrane (M) and nucleocapsid (N).
Diseases[change | change source]
- Severe acute respiratory syndrome coronavirus 2, which causes the disease coronavirus disease 2019 and is the cause of the COVID-19 pandemic (formerly referred as the "2019–20 coronavirus outbreak")
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 easy to grow in the laboratory.
Structure[change | change source]
Coronaviruses are large, spherical particles with unique surface projections. Their size is variable, averageing 80 to 120 nms The total molecular weight is on average 40,000 kDa. They are enclosed in an envelope studded with projecting protein molecules. These layers protect the virus when it is outside the host cell.
The viral envelope is made up of a lipid bilayer in which the membrane (M), envelope (E) and spike (S) structural proteins are anchored. The ratio of E:S:M in the lipid bilayer is approximately 1:20:300. The E and M protein are the structural proteins that combined with the lipid bilayer to shape the viral envelope and maintain its size. S proteins are needed for interaction with the host cells. But human coronavirus NL63 is peculiar in that its M protein has the binding site for the host cell, and not its S protein. The diameter of the envelope is 85 nm.
Related pages[change | change source]
References[change | change source]
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- enveloped = has viral envelopes covering their protective protein capsids; positive sense = the RNA sequence may be directly translated into the desired viral proteins.
- One kilobase = 1000 base pairs
- virion = complete virus particle.
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Virions acquired an envelope by budding into the cisternae and formed mostly spherical, sometimes pleomorphic, particles that averaged 78 nm in diameter (Figure 1A).
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See Figure 10.
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