Question

How are DNA and RNA viruses alike? How are they different?

Answer 1

Hm alright - I'll start with some of the differences.
You know, of course that they have different genetic material. This in turn requires them to replicate in different manners and require different 'equipment.'

Take, for example, your RNA viruses. You have those that jump right in and begin protein synthesis using that RNA - these viruses require a special enzyme to replicate said RNA to be packaged in the protein coats. You also have RNA viruses which utilize reverse transcriptase to create a DNA copy of itself to be inserted into the host genome - HIV would be the textbook example. Also worth noting here - nearly all animal viruses with RNA genomes have an envelope, as do some with DNA genomes (that factoid was taken out of Campbell's).

DNA viruses, it appears, target the nucleus and take advantage of the host cell's machinery (which is already suited for DNA replicatino and such) but also use their own enzymes. In contrast to RNA viruses (excluding the retroviruses), DNA viruses are able to integrate into the host cell genome - for example, herpesviruses DNA can remain in the nuclei of certain nerve cells.

This is a pretty incomplete answer, and I'll add more onto it as I research....good question though!

Answer 2

Is that cell integration the lysogenic cycle, meaning that RNA viruses (excluding retroviruses), are only able to undergo the lytic cycle? Also, why is it that retroviruses are an exception to this rule - I'm guessing it has something to do with the DNA copy?