DNA mismatch
From EvoWiki
DNA mismatch is a type of DNA damage where two non-complementary bases are paired, e.g. adenine with cytosine or thymine with guanine1. Mismatch errors occur during DNA replication.
Mismatch repair
The mismatch repair system is active shortly after DNA replication, before DNA methylation takes place. This means that the mismatch repair system knows which DNA strand is the parent strand, and which is the new strand, as the parent strand will be methylated, but the offspring strand will not be. This is important, as in a mismatch error it is the offspring strand which has the error.
The mismatch repair system begins with an enzyme called DNA glycosylase which travels along the DNA molecule, and upon finding a mismatch will remove the incorrect base leaving a gap. Another enzyme, apurinic/apyrimidinic endonuclease, which identifies the apurinic site and cuts the DNA backbone. An exonuclease then takes over and removes the backbone and a number of bases surrounding the mismatch site. DNA polymerase and DNA ligase then repair the DNA.
Footnotes
- Since adenine and guanine are larger than cytosine and thymine they are rarely paired, since they physically will not fit in the DNA molecule.
References
- Garrett, R.H. & C.M. Grisham, 1998. Biochemistry, 2nd ed. Saunders College Publishing, Orlando FL. Ch 29.
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This page is part of the EvoWiki encyclopedia of genetics and molecular biology. Topics: Genetics - Transmission genetics - Molecular genetics - Population genetics - Quantitative genetics - Molecular biology - Genomics |
