Single-strand break repair:

Hereditary defects in the repair of DNA damage are implicated in a variety of diseases, many of which are typified by neurological dysfunction and increased genetic instability and cancer. Of the different types of DNA damage that arise in cells, single-strand breaks (SSBs) are the most common, arising at a frequency of tens of thousands per cell per day from direct attack by intracellular metabolites and from spontaneous DNA decay. Single-strand breaks (SSBs) are discontinuities in one strand of the DNA double helix and are usually accompanied by loss of a single nucleotide and by damaged 5- and/or 3-termini at the site of the break.

Double-strand break repair:

Double-strand DNA breaks are common events in eukaryotic cells, and there are two major pathways for repairing them: homologous recombination (HR) and nonhomologous DNA end joining (NHEJ).

Homologous recombination repair (HR) is a DNA repair process that includes the invasion of an undamaged DNA molecule by a damaged molecule of identical or very similar sequence. Resynthesis of the damaged region is accomplished using the undamaged molecule as a template.

Non-homologous end joining (NHEJ) is a pathway that repairs double-strand breaks in DNA. NHEJ is referred to as “non-homologous” because the break ends are directly ligated without the need for a homologous template.

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