Biochemistry 2280A Chapter Notes - Chapter 16: Exonuclease, Chromosome, Cytochrome C Oxidase
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25 Dec 2016
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Even with proof reading mistakes occur every 1 in 10^7 nucleotides. This results in mismatched pairs that lead to change (mutation) in dna sequence: depurination: Acid results in loss of a or g base this results in an abasic site. When dna polymerase sees the abasic site it stops, so translesion dna polymerase comes and synthesis dna past the site by skipping it or adding in a new base (mutation). Once translesion polymerase passes the abasic site the normal dna polymerase continues dna synthesis: deamination: The amine group of a base (usually cytosine) is converted to carbonyl. Cytosine is usually converted to uracil after the deamination: pyrimidine dimers: Double bonds between adjacent pyrimidines (c,t,u) react to make a cyclobutane ring. This is commonly caused by uv radiation. Translesion dna polymerase is needed to synthesis dna past the pyrimidine dimers. Ionizing radiation(x-rays, gamma rays) cause modification to all 4 bases.