In nucleotide excision repair (NER), what role does DNA Helicase play?

In nucleotide excision repair (NER), DNA helicase plays a crucial role by unwinding the DNA helix at the site of damage. This action is essential for the repair process as it creates single-stranded DNA regions that can be accessed by other repair enzymes. Specifically, after the damaged section of DNA is recognized and excised, helicase ensures that the strands are properly separated, allowing for the replacement of damaged nucleotides by DNA polymerase.

The option regarding replacing damaged nucleotides pertains more to the function of DNA polymerase rather than helicase. While helicase does assist in the process by unwinding DNA, it does not have the capability to replace nucleotides itself. Similarly, the function of cutting single-stranded DNA is typically attributed to endonucleases in the repair pathway rather than helicase, which does not cut but rather unwinds. The sealing of the DNA strand is typically performed by DNA ligase, which re-establishes the phosphodiester bonds after the repair has taken place. Thus, while those activities are essential to NER, they are attributed to other enzymes, with helicase specifically responsible for the unwinding aspect of the repair process.