Final answer:
DNA polymerase's proofreading activity, through its 3' to 5' exonuclease function, corrects base-pair mismatches during DNA replication, improving replication fidelity by about 100-fold.
Step-by-step explanation:
The proofreading activity of DNA polymerase significantly improves the fidelity of DNA replication. DNA polymerase is equipped with a proofreading function, characterized by a 3' to 5' exonuclease activity, which allows it to detect and excise incorrectly paired nucleotides. If an incorrect base is added during replication, this exonuclease action enables the enzyme to remove the incorrect nucleotide. After excising the wrong base, DNA polymerase re-inserts the correct base, dramatically reducing the number of errors in the DNA sequence. This process enhances the accuracy of DNA replication by enabling the correction of mispairings that might have otherwise remained and led to mutations.
DNA replication is highly accurate to begin with, having an intrinsic error rate of as low as one error per 10 million nucleotides. However, with the addition of the proofreading mechanism, errors are even less frequent, improving the fidelity of DNA replication by a factor of approximately 100-fold.
Therefore, the final answer in two line explanation in 300 words: The proofreading activity of DNA polymerase improves the fidelity of DNA replication by approximately 100-fold. This is achieved through the exonuclease action that excises incorrectly paired bases and allows for their correction, ensuring high replication accuracy.