Final answer:
During DNA replication, DNA polymerase can make mistakes by adding wrong nucleotides, but it can correct such errors through its proofreading function. If these errors are not corrected by DNA polymerase or the mismatch repair system, they may lead to persistent mutations with serious consequences such as cancer.
Step-by-step explanation:
During DNA replication, the insertion of a wrong nucleotide is considered a proofreading failure. Typically, DNA polymerase has the ability to correct many of these mistakes through its proofreading function. When a new base is added, the enzyme reads the new base to check if it has paired correctly with the corresponding base in the template strand. If an incorrect nucleotide has been incorporated, the enzyme will excise the wrong nucleotide by making a cut at the phosphodiester bond through its 3' exonuclease activity. The incorrect nucleotide is then replaced with the correct one.
If mistakes go uncorrected, they can potentially result in mutations, which can lead to serious consequences such as cancer. However, there are mechanisms like mismatch repair, which address errors post-replication. The mismatch repair system recognizes the mispaired bases, excises the incorrect part, and fills in the gap with the correct nucleotide. In some cases where the repair mechanisms fail or the enzymes responsible for repair are defective, persistent mutations occur.