Final answer:
Nucleotide Excision Repair (NER) is the DNA repair mechanism that removes bulky lesions such as thymine dimers, commonly resulting from UV light damage, and restores DNA integrity by excision and replacement of a section of the DNA strand.
Step-by-step explanation:
The DNA repair mechanism used to repair bulky lesions in DNA, such as thymine dimers often caused by ultraviolet light exposure, is Nucleotide Excision Repair (NER). This process can handle lesions affecting larger sections of the DNA ranging from 2 to 30 bases, which includes not only thymine dimers but other distortions that alter the DNA helix. Nucleotide excision repair operates by removing a small section of the DNA strand containing the damaged nucleotides.
First, enzymes make a cut on both the 3' and 5' ends of the damaged base or bases. The abnormal segment is then excised and a DNA polymerase synthesizes the correct nucleotides using the undamaged complementary strand as a template. Finally, DNA ligase seals the gap by forming a phosphodiester linkage, restoring the integrity of the DNA molecule.