Methyl Mismatch Repair

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1. Methyl Mismatch Repair (MMR)
To repair mismatched bases, the system has to know which base is the correct one. In order to recognize the parental strand, the characteristic than can be detect isi it is a DNA strand that has been methylated. Once in a while, there will be times when the polymerase would accidentally place the wrong base across the template DNA strand during the replication of DNA. Usually it would detect it mistakes, and correct itself. But, if polymerase failed to fix its mistakes, there are some types of repair enzymes that would scan the DNA strand and proof reed the strand again. However, there might still be a wrongly placed base pair of the new strand compare to the parental strand. Figure 7 in page 15 show the pathways
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Nucleotide Excision Repair (NER)
NER is more complex biochemical complex than BER. The problem that needs NER system to repair the cell is when pyrimidine dimers occur. The nuclease will detect the mutation and remove the lesion on the DNA strand. Then polymerase will go through the DNA strand again and add new and correct base needed on that stand. Then ligase will seal the strand, and a new healthy DNA strand is born. Figure 9 in page 19 show the pathways in illustration of the process of MMR.

Consequences of DNA damages, cancer could be develop. This is because an unrepaired DNA damages, can cause errors when the cell is dividing. The cells will synthesis wrong code in DNA strand that lead to mutation and eventually to cancer. First and foremost, the DNA was damaged through exogenous or endogenous sources. When the damaged DNA were failed to be repair when it replicates in a new cell with a proliferative capacity (ability to spread rapidly), mutation conferring cellular growth will take advantages. Then, large areas of cells at a tissue surface or within any organ will be affected by the damaged DNA (Pre-malignant field defect). This damaged DNA is called as carcinogenic alteration, where, normal cells were converted into cancer cells. Figure 10 in page 21 explains on the process of cancer cell development. It all started with DNA damages that lead to mutation. Eventually, it leads to cancer if it is failed to be repair or remove the mutated DNA
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