Nucleotide Excision Repair (NER) is a crucial cellular process that repairs damaged DNA. It specifically targets bulky DNA lesions, such as those caused by ultraviolet (UV) light or chemical exposure. The repair mechanism involves recognizing the damage, unwinding the DNA, and removing a short single-stranded segment containing the lesion. After the damaged segment is excised, DNA polymerase fills in the gap by synthesizing new DNA, and DNA ligase seals the remaining nick in the sugar-phosphate backbone. This process helps maintain the integrity of the genome and prevents mutations that could lead to diseases like cancer.