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Definition: How does non-homologous end joining repair double-strand breaks?

NHEJ is a highly efficient and rapid repair mechanism that directly joins the broken ends of the DNA molecule without requiring a homologous template. This repair process is particularly important during the G1 phase of the cell cycle when sister chromatids are not available for homologous recombination.

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The process of NHEJ involves several key steps:

1. Recognition and binding: Proteins involved in NHEJ, such as Ku70 and Ku80, recognize and bind to the broken DNA ends. This binding stabilizes the DNA ends and prevents further degradation.

2. Processing of DNA ends: The DNA ends are processed by nucleases and polymerases to remove damaged or mismatched nucleotides and create compatible ends for ligation.

3. Ligation: The processed DNA ends are then ligated together by a DNA ligase enzyme, which forms a phosphodiester bond between the adjacent nucleotides, sealing the break.

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4. DNA repair synthesis: In some cases, NHEJ may involve a short DNA synthesis step to fill in any gaps or missing nucleotides at the site of the break. This synthesis is carried out by DNA polymerases.

While NHEJ is an efficient repair mechanism, it can occasionally introduce small insertions or deletions at the site of the break, leading to mutations. However, these mutations are generally considered less detrimental than the consequences of an unrepaired DSB.

Overall, non-homologous end joining is a critical DNA repair pathway that helps maintain the integrity of the genome by efficiently repairing double-strand breaks in the DNA molecule.

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Keywords: repair, homologous, joining, double, strand, breaks, molecule, nucleotides, synthesis