3.7: Virions

Viruses, when not within a host cell, exist as viral particles known as virions. A virion consists of some genetic material (DNA or RNA), a protein coat known as a capsid which protects the genetic material, and in some cases an outside envelope of lipids. Shapes are variable and size is typically on the order of \(\frac{1}{100}\) the size of bacterial cells.

Unlike Bacteria and Archaea, viruses do not grow by cellular division. Viruses do not have cells. Instead, they rely on their host cell to make copies of the virus, as noted at the end of Chapter 2. Their life cycle begins when they attach to a host cell and gain access to the cell interior. Next, they remove their capsid and release their DNA or RNA, which causes the host to replicate viral genetic material and proteins. Lastly, the viral particles assemble and can be released from the host cell.

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