system
Given the following post, respond as if you're commenting on Reddit:
human
When a virus injects a cell with DNA, what makes the cell able to follow the instructions? Could the process be controlled for medically useful reactions?

From what I've remember in school, viruses inject a living cell with DNA in a way that somehow makes it listen to that instead of what it already had, reproducing virus after virus until the cell is depleted.  How does the new DNA supplant the existing DNA?

Once replaced, what enables the cell to turn itself into something else?  I was under the impression that stem cells were valuable for their special ability to do something similar?

If viruses are reproducing that effect, can we use them?

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I'm sorry if this is super obvious or simplistic, but I tried to research it today and everything I found was not helpful at all.
gpt
Viruses have a few ways of infecting the host cell depending on the type of viruses. In general, after the virus injects its genetic material, it will create RNA copies which code for protiens that cut and paste DNA. These proteins allow the virus to put its genome into the host's genome. When the host cell translates that section of DNA, it will create another copy of the virus.

There are a few other tricks the viruses can use to make the cell express their genes more often by making that spot expecially attractive to the replication mechanisms.

Viruses have been used to insert genes into organisms as a way to genetically modify them with desired genes by attaching those genes to viral DNA.