Final answer:
Nucleotide excision repair (NER) is a DNA repair mechanism fixing damage like pyrimidine dimers from UV exposure. It involves cutting out damaged bases, filling the gap with DNA polymerase, and sealing the repair with DNA ligase.
Step-by-step explanation:
Nucleotide Excision Repair
Nucleotide excision repair (NER) is a crucial DNA repair mechanism that addresses and corrects DNA damage like pyrimidine dimers, which can result from UV exposure. The process involves several steps to ensure the DNA's integrity and proper functioning. Firstly, the damage is recognized, and a cut is made on both the 5' and 3' sides of the lesion. The erroneous nucleotides are then excised and removed. Subsequently, DNA polymerase comes into play, synthesizing new nucleotides to fill the gap based on the intact, complementary DNA strand. Finally, DNA ligase seals the strand by forming a phosphodiester linkage, restoring the phosphate backbone of the DNA molecule.
This mechanism differs from the repair of Okazaki fragments, which are short DNA sequences synthesized on the lagging strand during DNA replication at the origin of replication. While the Okazaki fragments also require DNA ligase to create phosphodiester bonds between fragments, they do not involve the specific removal and replacement of damaged bases.
The excision repair pathway ensures genome stability and is essential for cellular resistance to genotoxic stress, preventing mutations that could potentially lead to diseases such as cancer.