Which of the following best describes a virion?

• A. The host cell’s cytoplasm
• B. A bacterial cell that helps viruses replicate
• C. The infectious virus particle containing genetic material in a protein shell
• D. The viral enzyme that replicates DNA

Answer: (C)

A virion is the complete, infectious virus particle outside a host cell. It contains the viral genome (DNA or RNA) packaged inside a protective protein shell called a capsid, and many virions also have a lipid envelope with surface proteins. This structure protects the genome as the virus moves between hosts and provides the means to attach to and enter a new cell, delivering the genome to begin replication. The host cell’s cytoplasm is part of the cell that can be infected, not the infectious particle itself. A bacterial cell that helps viruses replicate isn’t describing the particle at all. A viral enzyme that copies DNA might be present inside some virions, but the virion is best defined as the infectious particle that contains the genome enclosed in a protein shell (and sometimes an envelope).