Why do RNA viruses appear to have higher rates of mutation?

A) RNA nucleotides are more unstable than DNA nucleotides.

B) Replication of their genomes does not involve the proofreading steps of DNA replication.

C) RNA viruses replicate faster.

D) RNA viruses can incorporate a variety of nonstandard bases.

E) RNA viruses are more sensitive to mutagens.

B) Replication of their genomes does not involve the proofreading steps of DNA replication.

Explanation:

RNA viruses have upto 1 billion time higher mutation rate than their host. As RNA is more fragile than DNA so these mutations are associated with the adaptability of RNA viruses in changing environment as well with their virulence. The higher mutation rates in RNA are the consequences of following factors.

The DNA of eukaryotes as well as of some viruses have the proofreading mechanism to repair mutations. Even some very high RNA viruses also poses this ability. But most of the viral RNA polymerases lack the ability of proofreading i. e. it cannot rectify the replication errors in RNA. It causes the higher mutation rate in viral RNA. Another comparatively small cause is the presence of uracil base in RNA instead of thymine. Sometime cytosine base changes to uracil and this is detected in DNA because DNA don't contain uracil while it cannot be detected in RNA because it already contains uracil.

B) Replication of their genomes does not involve the proofreading steps of DNA replication.

Explanation:j

1. This is because RNA polymerase do not proofread proteins or polymerase components to check for errors and repair.

2. Because RNA viruses usually encoded their replication machinery, therefore they have the ability to replication at high rate which increases chances for mutation, to any length and extent to suits their needs.

Therefore, since there is no check for the number of replication they can go through and no need for correction of replication errors, they have rapid chances for mutation and therefore virulence. Different offspring, with distinct genetic composition from wrong bases insertion and translation and therefore of virulence totally different from the parents will be produced. Thus mutagensis, and virulence continues to increase.