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Virus Biology Definition

Viruses are the cause of many infectious diseases, and the target of many vaccines. Viruses infect nearly all living things, from plants and animals down to the smallest bacteria. There is debate as to whether or not viruses are living.

  1. General Definition

    • An artist's depiction of DNA.

      Princeton University defines a biological virus as an "ultra-microscopic infectious agent that replicates itself only within the cells of a living host." A biological virus is a piece of genetic material, either DNA or RNA, surrounded by a protein covering. Viruses lack several important characteristics of living organisms, such as the ability to obtain and transform energy.

    DNA Viruses

    • DNA viruses carry DNA as their genetic material. Inside a host cell, the viral DNA is used by the host cell to reproduce the virus. Common DNA viruses include human papillomavirus, herpes and smallpox.

    RNA Viruses

    • RNA viruses, also known as retroviruses, carry RNA as their genetic material. Inside the host cell, viral RNA is copied to viral DNA. This DNA is incorporated into host chromosomes. Human immunodeficiency virus, or HIV, is an RNA virus.

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