DNA repair is an important line of defense against mutations. DNA repair mechanisms are responsible for correcting DNA damage created by mutations.  DNA repair mechanisms are divided into two categories in which they either repair damaged bases or repair incorrectly paired bases during replication. DNA repair is a multistep process that involves 3 main steps: 1) detection of irregularity within DNA structure, 2) removal of abnormal DNA, 3) replace error with normal synthesized DNA.

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Types of DNA Repair

 

One-step repair- MGMT, DNA repair protein, repairs the naturally occurring mutagenic DNA lesion back to guanine and prevents mismatch and errors during DNA replication and transcription.

Nucleotide excision repair (NER)- primarily repairs pyrimidine dime and bulky DNA adducts

Base excision repair (BER)-  repairs chemically modified bases such as uracil disincorporation and oxidative damage. DNA glycosylases recognize lesion and remove the base at glyosidic bonds producing abasic or AP site by base flipping out.

Mismatch repair (MMR)- corrects replication errors that have escaped DNA repair by using polymerases.

Recombination repair-repairs harmful double-strand breaks in DNA

 

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When genes such as tumor suppressor genes, and the various DNA repair mechanism are not functioning properly and do not fix DNA mutations, cells rely on apoptosis to rid the unwanted or damaged cells.