Final answer:
If a wrong nucleotide is placed during DNA synthesis, DNA polymerase can remove it using exonuclease activity and replace it with the correct one. Nucleotide excision repair is another mechanism that fixes more significant errors by removing a segment of DNA and copying the correct sequence.
Step-by-step explanation:
If a wrong nucleotide is placed during the regular 5' to 3' DNA synthesis, DNA polymerase can remove it and replace it with the correct nucleotide by resuming the exonuclease activity.
Most of the mistakes during DNA replication are promptly corrected by the proofreading ability of DNA polymerase. This enzyme reads the newly added nucleotide and uses its 3' exonuclease activity to cut the phosphodiester bond, releasing the incorrect nucleotide. After this, DNA polymerase resumes synthesis by adding the correct nucleotide.
In nucleotide excision repair, another repair mechanism, incorrect bases are removed along with a few bases on both ends. These bases are then replaced by copying the template with the help of DNA polymerase. DNA ligase then creates the necessary phosphodiester bond to seal the new fragment into the DNA strand.