Why are certain viruses referred to as "retro" viruses?

Certain viruses are referred to as "retro" viruses because they possess the unique ability to transcribe their genetic material from RNA into DNA. This process is facilitated by an enzyme called reverse transcriptase, which allows the viral RNA to be converted into DNA once it has entered the host cell. The newly formed viral DNA can then integrate into the host's genome, enabling the virus to replicate and persist within the host. This characteristic distinguishes retroviruses from other types of viruses that may use different strategies for genetic replication and expression.

The ability to reverse transcribe RNA into DNA is a key function that is critical to the lifecycle of retroviruses, including HIV. Understanding this mechanism is fundamental for developing antiviral therapies that target various stages of the viral replication process.