virions
Summary
A virion is a complete, infectious virus particle outside a host cell: a DNA or RNA genome inside a protein capsid, sometimes with a lipid envelope. It has no metabolism of its own, so new virions are made only when a host cell's machinery assembles them.
Detail
Meaning: A virion is a complete, infectious viral particle outside a host cell. It has a nucleic acid genome (DNA or RNA, single- or double-stranded) inside a protein capsid. Some virions add a lipid envelope taken from host membrane, carrying viral glycoproteins. A virion has no metabolism or ribosomes, so it cannot replicate alone. New virions are assembled in a host cell from newly made parts and released by lysis or budding.
On the MCAT: Passages follow a phage or retrovirus through attachment to a host receptor, genome entry, replication, assembly and release, or contrast the lytic and lysogenic cycles. Hershey-Chase labeled phage protein with 35S and phage DNA with 32P, then showed that the DNA entered the host cell and carried the genetic information.
Common confusion: A virion is not a cell, and it does not grow or divide by binary fission. The number of virions rises because infected cells assemble many new ones. Inside a cell the viral genome is being copied, and intact virions may not be present at that stage. Viroids (naked RNA) and prions (protein) are not virions.
Sources
- Campbell Biology
- Brock Biology of Microorganisms
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.