Cells tolerate higher rates of error in RNA synthesis because many copies of that RNA will be made, and only some of them have errors, which means that a high number of normal copies are also made, being enough to overcome and correct the problem. Another point is that DNA molecules are temporarily inherited. When it comes to errors in DNA synthesis, the mutation can be permanent if it`s not corrected until the next cell division, which makes errors in DNA synthesis more dangerous and with more consequences than in RNA synthesis, leading the cell to tolarate only a lower rate of errors.
