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Lecture 7

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Biology 1001A
Tom Haffie

IndependentStudyOutcomes 1. mechanism of proofreading and likely result of proofreading defects 2. mechanism of mismatch repair 3. differences among insertion sequences, transposons and retrotransposons 4. implications of insertion of mobile elements into DNA 5. why transposons are not actually "jumping" genes 6. basic structure of retrovirus genome 1. proofreading mechanism = dna polymerase backs up and removes mis-paired nucleotides from dna strand -if mismatched then reverse and use deoxyribonuclease to remove newly added incorrect nucleotide dna repair mechanism = use if proofreading can't detect mistake -repair enzymes move along double helix scanning for distortions -if there is a distortion, they remove portion of new chain and dna polymerase (using template strand as guide) seals the nucleotide chain into dna molecule -result of proofreading defects lead to mutations! 2. -next phase to increase accuracy of dna replication after proofreading mechanism 3. insertion sequence = small, contain only gene for transposition (transposase), at 2 ends of IS, short inverted repeat sequence, which enables transposase to identify the ends of the TE when it catalyzes transposition transposons = inverted repeat sequence at each end enclosing a central region with its genes -carry non insertion sequence genes as TE moves from place to place retrotransposons= transpose by copy and paste mechanism, occurs via intermediate rna copy of TE -reverse transcriptase use rna as template to make dna copy of retrotransposon 4. -TE = biological mutagens and INCREASE GENETIC VARIABILITY! 5. -transposons are never in the air or jumping between one location and another -transport into genes and knock out function CONTACT BETWEEN THE TE AND TARGET SITE -like recombinantion! 6. -direct repeats at eithe
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