The genomic content of viruses can be made of RNA or DNA and can be single-stranded or double-stranded.

All viruses have genetic material made of nucleic acids. You, like all other cell-based life, use DNA as your genetic material. Viruses, on the other hand, may use either RNA or DNA, both of which are types of nucleic acid. Two differences distinguish DNA from RNA: RNA contains the sugar ribose. In contrast, DNA contains the sugar deoxyribose – hence DNA and RNA and RNA has the nucleic acid uracil while DNA contains Thymine.

We often think of DNA as double-stranded and RNA as single-stranded, since that’s typically the case in our cells. However, viruses can have all possible combos of strandedness and nucleic acid type (double-stranded DNA, double-stranded RNA, single-stranded DNA, or single-stranded RNA). Viral genomes also come in various shapes, sizes, and varieties, though they are generally much smaller than the genomes of cellular organisms.

Notably, DNA and RNA viruses always use the same genetic code as eukaryotic and prokaryotic cells. This similarity allows them to infect host cells and use the genetic material and proteins in the host cell to produce copies to reproduce. If they didn’t have similar genetic material, they would have no way to reprogram their host cells!