DNA mutation, excision repair of DNA lesions, triple repeat mutations

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Soil + Crop Sciences
SOCR 330
Sarah Ward

7 November Molecular Basis for Mutation Mutations result from Rearrangement of sections of genome Change in nucleotide sequence Change in single nucleotide pair is a point mutation Change on one base always results in change in complementary base on opposite DNA strand Effect of point mutation varies from none to major depending on location of change in DNA sequence Point Mutations Substitution (changing one base for another) Transitions change purine → purine (A ↔ G) or pyramidine → pyramidine (C ↔ T) Transversions change purine ↔ pyramidine (T ↔ A, C ↔ G, etc.) Transitions less likely to be detected and repaired Frameshift Mutations Deletion: loss of base AAT(A)GCA → AATGCA Addition: insertion of extra base AATAGCA → AATTAGCA Frameshifts have major effects: change all codons downstream Silent, Mis-Sense and Non-Sense Point Mutations Silent mutation has no effect on gene function AGA (ser) → AGG (ser) Mis-sense mutation changes amino acid GAA (leu) → GGA (pro) Non-sense mutation causes premature termination of translation ATG (tyr) → ATC (stop) All downstream amino acids in polypeptide lost Effect of a Missense Point Mutation Normal beta-globin polypeptide Glutamic acid is 6 amino acid (GAG) Sickle-cell beta-globin polypeptide Valine is 6 amino acid (GTG) Common Causes of Spontaneous Point Mutations Deamination Loss of NH 2roup from a
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