Joklik, W. K. Department of Microbiology and Immunology, Duke University Medical Center, Durham, North Carolina.
Pierce, Marcia M. Department of Biological Sciences, Eastern Kentucky University, Richmond, Kentucky.
Last reviewed:March 2019
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- Recognition of viruses
- Morphology and size
- Viral genomes
- Viral proteins
- Virus–cell interaction
- Lytic interaction
- Transforming interaction
- Antiviral chemotherapy
- Links to Primary Literature
- Additional Readings
Any of the elementary infectious agents that possess some of the properties of living systems, such as having a genome and being able to adapt to changing environments. Viruses comprise a large group of infectious agents ranging from 10 to 400 nanometers in diameter. They are capable of infecting all animals, plants, and bacteria. However, because viruses are not functionally active outside their host cells, they are totally dependent on living cells for reproduction and metabolism. In general, viruses share three characteristics: (1) a simple, acellular organization consisting of a nucleic acid genome surrounded by a protective protein shell, which may itself be enclosed within an envelope that includes a membrane; (2) the presence of either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), but not both; and (3) an inability to reproduce independent of host cells. In essence, viruses are nucleic acid molecules, that is, genomes that can enter cells, replicate in them, and encode proteins capable of forming protective shells around them (Fig. 1). See also: Animal virus; Deoxyribonucleic acid (DNA); Genomics; Infection; Nucleic acid; Ribonucleic acid (RNA); Virus classification; Virus infection, latent, persistent, slow
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