Final answer:
In molecular cloning, mismatch repair is finalized by DNA ligase sealing the strand after DNA polymerase fills in the correct nucleotides, restoring the DNA's integrity.
Step-by-step explanation:
During molecular cloning, repairing the phosphodiester backbone of DNA after mismatch repair involves several enzymatic steps. After mismatch repair proteins detect and remove the incorrectly added base from the newly synthesized strand, the gap left behind must be filled with the correct nucleotide. This is done by DNA polymerase, which adds the correct nucleotide. Finally, the DNA strand is sealed by the enzyme DNA ligase, restoring the continuous phosphodiester backbone of the DNA molecule. In the case of nucleotide excision repair, which is similar but deals with damaged bases rather than mismatched ones, the process also concludes with DNA ligase sealing the nucleotides into place after DNA polymerase has added the correct bases.