Viruses have either DNA or RNA as their genomic material, whereas cells—including bacteria—have both. In DNA viruses, the synthesis of viral DNA is similar to how the host cell would normally carry out DNA synthesis; in other words, the virus inserts its genetic material into the host’s DNA. In RNA viruses, transcription (the first stage of protein synthesis, in which messenger RNA is produced from the DNA) takes place with the help of RNA polymerase.