Why does a virus not have both DNA and RNA?

Answer 1

Because it doesn't use it's DNA or RNA to function, it uses it to inject into a cell and switch the cell's instructions to its own so the cell will make more viruses. Cells have DNA and RNA to tell the cell what to do, but viruses just do it naturally. Viruses have no use for both.

Answer 2

Viruses that are made of DNA use the host cell's enzymes to synthesize the RNA needed to synthesize viral proteins. Viruses that contain RNA have an enzyme called reverse transcriptase which they can use to synthesize DNA from an RNA template. Thus, they don't need to have both.

Answer 3

Different kinds of viruses can contain either DNA or RNA. This is encapsulated in a protein shell. Some viruses are also enclosed in a lipid bilayer, like cells.