BIOL 240 1st Edition Lecture 20Outline of Last Lecture I. Coordinating synthesis of leading and lagging strandsII. TelomeresOutline of Current Lecture I. Telomere DysfunctionII. Holliday Model of Genetic RecombinationIII. Double Strand Break ModelCurrent LectureI. Telomere Dysfunction- Caused by telomerase mutationsII. Holliday Model of Genetic Recombination1. A pair of non-sister chromatids are aligned as a tetradThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Chromatids are nicked in corresponding locations 3. The broken strands exchange with one another—strand exchange enzymes4. The breaks in the strands join—DNA ligase 5. Branches migrate; further strand exchange creates long regions of heteroduplex DNA6. Coordinated nicking at the branchpoint7. Re-ligation creates crossover chromatidsIII. Double Strand Break Model1. Endonuclease Spo11 makes double-strand breaks at random sites along chromatids to initiate recombination.2. MRX “resects” 5’ ends to create long 3’ single-strand tails.3. Strand-exchange enzymes Rad51 and DMC1 form filaments on single-strand tails.These filaments can find and pair with complementary sequences in fully base-paired duplex DNA.4. Rad51 mediates strand invasion to create D-loop. DMC1 filament from other side of break captures extruded strand of
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