Today, we can see viruses using electron microscopes and we know much more about them. Viruses are distinct biological entities; however, their evolutionary origin is still a matter of speculation. In terms of taxonomy, they are not included in the tree of life because they are acellular (not consisting of cells). In order to survive and reproduce, viruses must infect a cellular host, making them obligate intracellular parasites. The genome of a virus enters a host cell and directs the production of the viral components, proteins and nucleic acids, needed to form new virus particles called virions. New virions are made in the host cell by assembly of viral components. The new virions transport the viral genome to another host cell to carry out another round of infection.
Characteristics of Viruses
Characteristics of Viruses
- Infectious, acellular pathogens
- Obligate intracellular parasites with host and cell-type specificity
- DNA or RNA genome (never both)
- Genome is surrounded by a protein capsid and, in some cases, a phospholipid membrane studded with viral glycoproteins
- Lack genes for many products needed for successful reproduction, requiring exploitation of host-cell genomes to reproduce