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Non-Homologous End Joining (NHEJ)

Non-Homologous End Joining (NHEJ) is a DNA repair mechanism that plays a crucial role in repairing double-strand breaks (DSBs) in the genome. DSBs are severe DNA lesions that can occur due to various factors, including exposure to ionizing radiation, certain chemicals, or errors during DNA replication.

Repairing Double-Strand Breaks

When a DSB occurs, NHEJ is one of the primary pathways that cells utilize to repair the break and restore the integrity of the DNA molecule. NHEJ is particularly important during the G1 phase of the cell cycle when the sister chromatid is not available as a template for repair.

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The process of NHEJ involves several steps:

Recognition and Binding: Proteins involved in NHEJ, such as the Ku70/Ku80 heterodimer, recognize and bind to the broken DNA ends.

Processing: The broken DNA ends are processed by nucleases and polymerases to remove damaged or non-complementary nucleotides.

Alignment and Ligation: The processed DNA ends are aligned and joined together by DNA ligase IV, along with other associated proteins.

End Restoration: Additional processing steps may occur to restore the original DNA sequence, although this can sometimes result in small insertions or deletions at the repair site.

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NHEJ is known for its flexibility and ability to repair DSBs in a relatively quick and efficient manner. However, due to its error-prone nature, NHEJ can occasionally introduce mutations or chromosomal rearrangements during the repair process.

Overall, NHEJ is a vital DNA repair mechanism that helps maintain genomic stability by efficiently repairing DSBs, thereby preventing the accumulation of potentially harmful mutations and ensuring the longevity of cells and organisms.

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