Final answer:
The statement is false because in nucleotide excision repair, a nuclease makes cuts on both the 3′ and 5′ ends of the damaged DNA to remove the segment, rather than only from the 5′ end. The segment is then replaced and the gaps are sealed to complete the repair.
Step-by-step explanation:
The statement that the first step in repair requires a nuclease to remove a stretch of base pairs from the 5′ end of each strand at the site of the break is false. In DNA repair, the typical process involves recognition of the damaged site, followed by the removal of incorrect or damaged bases. Specifically, in nucleotide excision repair (NER), a nuclease makes cuts on both the 3′ and 5′ ends of the damage, removing a segment of DNA.
This segment is then replaced with the correctly paired nucleotides with the action of DNA polymerase. Once the bases are filled in, the gaps are sealed with a phosphodiester bond catalyzed by DNA ligase. In contrast, the passage refers to a different scenario where, after a double-stranded break, the repair process involves proteins like Ku to first bring the DNA strands together.
This may also involve the creation of staggered ends and the formation of hydrogen bonds before DNA ligase seals the repair. However, the initial nuclease action at a blunt-ended double-stranded break does not specifically remove a stretch from the 5′ end of each strand but rather involves trimming back the DNA and creating overlapping ends suitable for repair.