Question

What is a prophage, a provirus, and an episome? What is their common role in a viral reproductive cycle?

Short answer

A prophage is a bacteriophage genome integrated into the bacterial DNA chromosome or existing as an extrachromosomal plasmid. A provirus is a virus genome integrated into the DNA of a host cell. An episome is a genetic element that can replicate independently as a plasmid or integrate into the host chromosome. Their common role in a viral reproductive cycle is to integrate their genomes into the host cell's DNA, permitting viral genetic information to be passed on when the host cell divides.

Step-by-step solution

Defining Prophage

A prophage refers to a bacteriophage (type of virus) genome inserted and integrated into the circular bacterial DNA chromosome or exists as an extrachromosomal plasmid. This situation is unique to bacteria and is a stage of the viral reproductive cycle known as lysogeny.

Defining Provirus

A provirus is a virus genome that is integrated into the DNA of a host cell. In the case of HIV, a provirus can remain dormant within the cell while continuing to replicate with the cell. It's an important stage in retroviral reproduction.

Defining Episome

An episome is a genetic element that can replicate independently as a plasmid or can integrate into a host chromosome. It serves as a subset of plasmids.

Common Role in Viral Reproductive Cycle

The common role of a prophage, provirus, and episome in the viral reproductive cycle is to integrate their genomes into the host cell's DNA, allowing for viral genetic information to be passed on when the host cell divides. This process is part of the lysogenic cycle in viruses, allowing them to reproduce without causing immediate lysis (death) of the host.