A virus is basically a gene transporter with the express purpose of infecting another cell in order to replicate. The virus consists of genetic material, either DNA or RNA, protected by a protein shell called a capsid. This capsid is typically self-assembled by proteins created by the viral genetic material. Some viruses however do assist in the construction of the capsid.
The first morphological type is the helical virus. The helical virus has a single type of protein in the shape of an enclosed tube, surrounding the genetic material, that resembles a spiral staircase. This causes the virus to be long and flexible, or short and rigid. The longer a helical virus, the more flexible it must be to prevent forces from snapping it. The length of the virus capsid is dependant on the length of the genetic material and the width of the virus depends on the length and arrangement of the proteins of the capsid.
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Virus classification is the process of naming viruses and placing them in a ‘family tree’ in relation to other viruses. This process is different from the one used to classify plants or animals. Thanks to the fossil record, there are clear connections between most animals or plants. Viruses do not leave such a record, so it is more difficult to determine relationships between them. Another factor causing difficulties in virus classification is their pseudo-living nature, many scientists are debating whether viruses should be considered alive because they are missing several criteria considered important for living creatures. This makes viruses very difficult to place in the current classification system for plants and animals.
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Many people are exposed to viruses and become sick, but for the majority of the population, they have no idea what a virus actually is. A virus is something that causes an illness and it is contagious. At its most basic level a virus is just a strand of DNA surrounded by a protein shell, which is what makes it different from other fragments of DNA such as prions and viroids. A virus cannot reproduce outside of a host cell and is considered by many scientists as not being truly ‘alive’. Viruses can infect plants and animals and some are even able to infect bacteria.
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