Final answer:
The fidelity of DNA replication is greatly enhanced by the proofreading activities of DNA polymerases, which can correct the majority of errors by detecting and removing mismatched nucleotides, then replacing them with the correct ones. This contributes to a very low error rate in the DNA replication process.
Step-by-step explanation:
The fidelity of DNA replication is significantly increased by the proofreading function of DNA polymerases. DNA polymerases have an inherent error rate of about one mistake per 107 nucleotides. However, with the addition of the proofreading mechanism, these enzymes can correct most mistakes that occur during the replication process. When an incorrect nucleotide is inserted, the polymerase can detect the mismatch, pause replication, and utilize its 3' exonuclease activity to remove the incorrectly paired base. After removal, it can then insert the correct nucleotide.
This proofreading capability is one of several repair mechanisms that work to minimize mutations in the DNA sequence. Collectively, these mechanisms, including those facilitated by DNA polymerases I and II which are known for their proofreading and repair functions, make errors in DNA replication quite rare.
The process is even more remarkable when considering the replication speeds. For example, E. coli can replicate its approximate 4.6 million base pair genome in just 42 minutes, with an average rate of adding 1000 nucleotides per second, thanks in part to these precise and efficient proofreading mechanisms.