How do you repair broken DNA?

Most damage to DNA is repaired by removal of the damaged bases followed by resynthesis of the excised region. Some lesions in DNA, however, can be repaired by direct reversal of the damage, which may be a more efficient way of dealing with specific types of DNA damage that occur frequently.

What happens when DNA double strand breaks?

Double-strand breaks in DNA can be lethal to a cell. And, if not repaired correctly, DSBs can cause deletions, translocations, and fusions in the DNA. These consequences are collectively referred to as genomic rearrangements, and they are commonly found in cancerous cells (Figure 1) (Aplan 2006).

What is double strand break?

Abstract. The DNA double-strand break (DSB) is the principle cytotoxic lesion for ionizing radiation and radio-mimetic chemicals but can also be caused by mechanical stress on chromosomes or when a replicative DNA polymerase encounters a DNA single-strand break or other type of DNA lesion.

What is the most common form of double stranded DNA repair?

The most common form of homology-directed repair is called homologous recombination (abbreviated HR), which has the longest sequence homology requirements between the donor and acceptor DNA.

What is the role of DNA strand breaks in genetic recombination?

In meiotic cells, double-stranded DNA breaks are programmed, and the ensuing recombination serves to link homologous chromosomes via crossovers to ensure their proper segregation during the first meiotic division.

What is excision repair of DNA?

Excision-repair pathways involve the removal or “excision” of a stretch of DNA containing damaged DNA and the resulting gap is filled in by DNA replication using the undamaged DNA as a template. In the 1960s, several groups discovered key aspects of the NER pathway in bacteria and in mammalian cells.

What is double-strand of DNA?

Double-stranded DNA consists of two polynucleotide chains whose nitrogenous bases are connected by hydrogen bonds. Within this arrangement, each strand mirrors the other as a result of the anti-parallel orientation of the sugar-phosphate backbones, as well as the complementary nature of the A-T and C-G base pairing.

How do you induce double-strand breaks in DNA?

DNA double-strand breaks (DSBs) are one of many types of DNA damage that occur spontaneously in all living organisms. DSBs can be induced by ionizing radiation, radiomimetic chemicals or reactive oxygen species, but also during DNA replication when a polymerase encounters a single-strand lesion at a replication fork1.

How does a DNA repair system work?

Thus, enzymes known as DNA glycosylases remove damaged bases by literally cutting them out of the DNA strand through cleavage of the covalent bonds between the bases and the sugar-phosphate backbone. The resulting gap is then filled by a specialized repair polymerase and sealed by ligase.