virus - (n.)

An infectious particle consisting essentially of a protein-coated or membrane enveloped DNA or RNA genome that codes for the constituents of the virus : Some viruses contain additional components, and their genomes additional genes : RNA viruses, in particular, have to provide the replicase or reverse transcriptase needed for their replication : Viruses enter certain prokaryotic or eukaryotic cells and multiply within these cells with the help of the local metabolism and enzyme machinery, often causing injuries or death of the infected cells. ~ See Also: Replicase, Retrovirus, Reverse transcriptase.