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Types of DNA Repair
To understand this first we have to understand the major types of DNA mutations.
Types of DNA Mutations
There are 3 major types of DNA mutations:
- Thymine Dimer Repair (G1).
- Mismatched Base Repair (G2)
- Cytosine Deamination Repair (G1)
Thymine Dimer Repair
There are Thymine bases that are adjacent to each other.
Due to ultra-violet radiation sometimes two Thymine bases form a dimer with each other by forming a covalent bond.
This is explained in the previous post regarding the disease Xeroderma pigmentosum.
Mismatch repair occurs in the G2 phase.
There are 2 genes responsible, hMSH2 and hMLH1.
These genes make sure if there is any mismatches in DNA, they are repaired.
But if any one of them is missing then there is no repair and this may cause the disease known as HNPCC (Hereditary Non-Polyposis Colorectal Carcinoma), also known as Lynch Syndrome.
Cytosine Deamination occurs in G1 phase.
In this the cytosine deamination occurs and cytosine is converted to uracil.
If the enzymes Uracil glycolase and AP endonuclease are absent, then as a result Uracil is formed and it accumulates.