Final answer:
Nucleotide excision repair is a crucial DNA repair mechanism that fixes mutations like thymine dimers caused by UV light. Enzymes cut and remove damaged DNA, and DNA polymerase and DNA ligase fill in and seal the gap to maintain DNA integrity.
Step-by-step explanation:
Nucleotide Excision Repair
Nucleotide excision repair (NER) is a critical DNA repair process that corrects DNA lesions such as thymine dimers, which are often caused by ultraviolet (UV) light exposure. This mechanism involves an enzyme complex that first recognizes the distorted DNA around the damaged site, such as a thymine dimer, then introduces cuts on both the 3' and 5' ends of the damage. The damaged strand segment is removed, and DNA polymerase fills in the gap with the correct nucleotides, using the undamaged strand as a template to ensure fidelity. Finally, DNA ligase seals the strand by forming a phosphodiester bond, restoring the DNA's integrity.
NER plays a vital role in maintaining genomic stability and protecting against mutations that can lead to cancer. Individuals with defective NER pathways display heightened sensitivity to sunlight and are prone to developing skin cancers at an early age due to the accumulation of unrepaired DNA damage.