6. DNA+replication


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Unformatted text preview: ing Strand­directed mismatch repair Strand­directed mismatch repair DNA replication summary DNA replication summary • DNA replication takes place at replication forks. • DNA replication takes place continuously only on the leading strand. On the lagging strand, short DNA fragments are made by a backstitching process. • DNA replication requires the cooperation of many proteins: DNA polymerase DNA primase, DNA helicases, Single­strand DNA­binding proteins DNA ligase et al • DNA replication fidelity DNA synthesis starts at replication origins DNA synthesis starts at replication origins Eukaryotic chromosomes contain multiple origins of replication. DNA synthesis phase (S phase): 40 min­ 8 hour Identifying replication origins Identifying replication origins How to make a DNA library How to make a DNA library DNA restriction enzyme ARS and ORC ARS and ORC • Autonomously Replicating Sequences (or ARSs for short) • ORC = Origin Recognition Complex • ARSs contain a DNA sequence termed the ACS (ARS Concensus Sequence) and ORC binds to the ACS. Histone modification can be inherited Histone modification can be inherited during replication Centromeres Centromeres Centromeres Centromeres End replication problem End replication problem Telomere and telomerase Telomere repeating sequences Why need to add sequence •Problem with how they are replicated completely •Leading vs lagging •Needs double strand template to bind to Telomerase shorter (info lose)cell death •As important genetic elements at the end of chromosomes lose crucial info each time of replication • protect genetic integrity •Require 3’ hydroxyl group so primer needed end of lagging becomes shorter need telomerase (reverse transcriptase activity) Telomere and telomerase Telomere and telomerase • Replication • Capping of chromosome ends • Measuring stick for cell divisions: replicative cell senescence http://www.ibioseminars.org/lectures/cell­bio­a­med/elizabeth­ blackburn.html...
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