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Lecture 26.pdf

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Biology (Sci)
BIOL 202
Daniel Schoen

Sarah Margareta IbrahimFriday March 15th 2013BIOL 202Basic GeneticsLecture 26 Mutations II Mutagens RepairConsequencesWhat were going to talk about today001234564Questions are similar to the exam type of 7383questions9623Some questions from last classoMutagensinduced mutations Mechanisms Detection of mutagensAmes test oCan the codon AAG be altered by spontaneous deamination of methlyC to ToDNA repair Mechanisms Hipfner Biol 202 1 oIn thinking about effects of base substitution have to remember that there are always two strands to DNA But we often only write one usually the First question Yes If you have an AAG codon you coding strand which is the same in sequence as have to remember that the DNA is double stranded the mRNAwith U substituted for T in mRNA So that means on the other stand you have a TTC Hipfner Biol 202 3 Which will change it to a GC mismatch So even if theres no C in the sequencealways remember that DNA is double stranded Think about the complementary strand by convention we only write the coding strand but remember that theres a noncoding strand as wellQuestion two The difference is that the mutation in the case of a nonsense mutationits the site of the mutation that creates the stop codon whereas in a oWhats the difference between a nonsense and frameshift mutation the insertion or deletion causes frameshift mutation if both lead to early truncation of the encoded protein the rest of the coding sequence to shift and somewhere downstream of that youll hit an out of oCan an indel mutation create a nonsense frame stop codon thats now in framemutation rather than a frameshift or both Question three related Yes If you have a sequence like TATAGAif you insert a G after the rst A you get TAG which is the stop codon Then downstream you still have a frameshift and everything downstream is out of sync But the actual Hipfner Biol 202 4 base pair that youve inserted has created a nonsense mutation so there are examples of insertions that are both a frameshift and a nonsenseQuestion four You can change a stop codon to an amino acid coding one So if you have TAA and you oWhat do you call a base substitution mutation that convert it to TAC youve changed the stop codon changes a stop codon to an amino acidcoding one into an amino acid coding codon Youre going to get Nonstop mutationReadthrough mutation a longer protein and youre going to again go until you hit the next random in frame stop codon This is called a nonstop change There are diseases that happen because of this1Hipfner Biol 202 5
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