Question

Why do RNA viruses mutate faster than DNA viruses?

Answer 1

Viral genetic material can vary greatly. Some viruses have RNA in their core, others have DNA. RNA can be single stranded on one copy or more than one, DNA is generally double stranded. As long as the required genes are present that is what matters.

Complete answer:
In DNA viruses, the genetic material will use the host cell’s DNA polymerase to replicate. DNA polymerase is an enzyme that not only makes new DNA strands, but also corrects errors as it goes along. Because of this proofreading function, mistakes made in the growing strand are usually corrected. This ensures that the new DNA molecule is the exact same as the parent strand. When new viral particles are being produced, each length of DNA that has to be packaged into the new viroid will have been checked for errors.

In an RNA virus, the steps are more complicated. First, reverse transcriptase will synthesise the viral DNA, which then integrates into the host cell, allowing the production of viral proteins. However, when it is time for new viroids to be made, the viral RNA has to be transcribed off the DNA. Viral RNA polymerase does not have an efficient proofreading mechanism, allowing for a greater number of errors which can be a million times higher than the host cell. So the new strands of viral RNA are going to have greater mutations.

Note: While this high rate of mutation can be beneficial, it also has the possible chance of causing the virus to become non-viable as the RNA strands are too small to take too many mutations. The virus has to maintain this below the lethal limit.