Question

which step of the double holliday junction pathway is directly responsible for ensuring that no information is lost at the site of the original dna double-strand break?

• nuclease trimming of the exposed ends of the dna at the break
• recognition of the dna double-strand break
• holliday junction resolution
• dna strand invasion
• dna synthesis

Explanation:

Identify the biological challenge of a double-strand break

A double-strand break (DSB) results in the loss of physical continuity and often the degradation of nucleotides at the broken ends. To repair this break without losing genetic information, the cell must use an undamaged homologous template to copy the missing sequence.

Analyze the role of homologous recombination

Using the Homologous Recombination Repair pathway, the cell processes the broken ends to generate 3' single-stranded overhangs. These overhangs invade a homologous, intact duplex template.

Evaluate the step that restores lost sequence information

Using the Double Holliday Junction Model, once strand invasion occurs, the invading 3' end serves as a primer. The key step that physically copies the genetic information from the intact homologous template to fill in the gap created by the break is DNA synthesis. Without this synthesis step, the genetic information lost during the break and subsequent resection would not be restored.

Compare the given multiple-choice options

• Nuclease trimming removes nucleotides, actually causing a temporary loss of information at the break site to prepare for invasion.
• Recognition of the break initiates repair but does not restore sequence information.
• Holliday junction resolution cleaves the junctions to separate the duplexes at the end of the process.
• DNA strand invasion aligns the homologous sequences but does not itself copy the missing sequence.
• DNA synthesis uses the homologous template to actively reconstruct the missing genetic information.

Answer:

• Nuclease trimming of the exposed ends of the DNA at the break
• Recognition of the DNA double-strand break
• Holliday junction resolution
• DNA strand invasion
• DNA synthesis (Correct answer)