Influenza Virus Particles Credit: Dr. F. A. Murphy/CDC

Viruses are unique. They have been classified as both living and nonliving at various points in the history of biology.

A virus particle, also known as a virion, is essentially a nucleic acid (DNA or RNA) enclosed in a protein shell or coat.

Viruses cannot replicate or express their genes without the help of a host.

Do you know what viruses that infect bacteria are called? Take the Virus Quiz!

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