Viruses are classified mainly by the nucleic acid in their genome. DNA viruses have a genome made of DNA, which in most of them is double-stranded (dsDNA). A few, such as parvoviruses, have single-stranded DNA.Examples of DNA viruses include:
• bacteriophages such as lambda (λ) phage and T4 phage, which infect E. coli
• herpes simplex virus (cold sores) and varicella zoster virus (chickenpox and shingles)
• adenoviruses (some respiratory infections)
• human papillomavirus (HPV) (warts and some cervical cancers)
• variola virus (smallpox)Because the host cell already uses DNA as its genetic material, a DNA virus can often use the host's own enzymes. In eukaryotic hosts, most DNA viruses enter the nucleus, where host RNA polymerase transcribes the viral genes into mRNA, and host (or viral) DNA polymerase copies the viral DNA. The mRNA is translated on host ribosomes to make capsid proteins and enzymes.DNA is chemically more stable than RNA, and DNA polymerase proofreads the new strand. As a result, DNA viruses usually have a lower mutation rate than RNA viruses, so they change more slowly and vaccines against them tend to stay effective for longer. Smallpox, a DNA virus, is the only human disease to have been eradicated by vaccination.Many DNA viruses can follow either a lytic pathway or a latent (lysogenic) pathway inside their host, which are covered in later lessons.
• bacteriophages such as lambda (λ) phage and T4 phage, which infect E. coli
• herpes simplex virus (cold sores) and varicella zoster virus (chickenpox and shingles)
• adenoviruses (some respiratory infections)
• human papillomavirus (HPV) (warts and some cervical cancers)
• variola virus (smallpox)Because the host cell already uses DNA as its genetic material, a DNA virus can often use the host's own enzymes. In eukaryotic hosts, most DNA viruses enter the nucleus, where host RNA polymerase transcribes the viral genes into mRNA, and host (or viral) DNA polymerase copies the viral DNA. The mRNA is translated on host ribosomes to make capsid proteins and enzymes.DNA is chemically more stable than RNA, and DNA polymerase proofreads the new strand. As a result, DNA viruses usually have a lower mutation rate than RNA viruses, so they change more slowly and vaccines against them tend to stay effective for longer. Smallpox, a DNA virus, is the only human disease to have been eradicated by vaccination.Many DNA viruses can follow either a lytic pathway or a latent (lysogenic) pathway inside their host, which are covered in later lessons.