DN Replication and Repair
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DN Replication genetic information is passed on to the next generation semi-conservative Parent molecule with two complementary molecules Parental strands separate Each parental strand is a template Each daughter DN molecule consists of one parental and one new strand
Overview of replication Initiation DN is unwound and stabilized Origins of replication: Replication bubble and replication fork Priming RN primers bind to sections of the DN and initiate synthesis Elongation Leading strand (5 3 ) synthesized continuously Lagging strand synthesized discontinuously then fragments are joined RN primer replaced by DN Proofreading Mismatch repair by DN polymerase Excision repair by nucleases
Review of DN structure double helix each strand has a 5 phosphate end and a 3 hydroxyl end strands run antiparallel to each other - pairs (2 H-bonds), - pairs (3 H-bonds)
SEP 1 Initiation at origins of replication separation sites on DN strands Depend on a specific -rich DN sequence Prokaryotes one site Eukaryotes multiple sites Replication bubble Replication fork Proceeds in two directions from point of origin
he proteins of initiation 1. Helicase unwinds double helix 2. Single-strand binding proteins holds DN apart 3. opoisomerase relieves strain by breaking, swiveling, rejoining strands
SEP 2 Priming initiation of DN synthesis by RN RN primers bind to unwound sections through the action of primase leading strand only 1 primer lagging strand multiple primers replaced by DN later
SEP 3 Elongation of a new DN strand lengthening in the 5 3 direction DN polymerase III can only add nucleotides to the 3 hydroxyl end Leading strand - DN pol III adds nucleotides towards the replication fork; - DN pol I - replaces RN with DN Lagging strand - DN pol III - adds Okazaki fragments to free 3 end away from replication fork - DN pol I - replaces RN with DN - DN ligase joins Okazaki fragments to create a continuous strand
SEP 4 Proofreading correcting errors in replication Mismatch repair DN pol III proofreads nucleotides against the template strand Excision repair nuclease cuts damaged segment DN pol III and ligase fill the gap left elomeres at 5 ends of lagging strands no genes, only 100 1000 sequences to protect genes telomerase catalyzes lengthening of telomeres
DN Replication and Repair 1. Summarize the central dogma in a diagram. 2. Define antiparallel and semiconservative in terms of the structure of DN. 3. Use the following terms associated with replication and create a flowchart showing the different stages: replication bubble and replication fork, helicase, single-strand binding proteins, RN primer, primase, leading strand, lagging strand, DN polymerase III, DN polymerase I, DN ligase, Okazaki fragments, and 5 à 3. 4. Differentiate between mismatch and excision repair. 5. What are telomeres and what role do they play in protecting the integrity of the lagging strand of the DN?
Modelling 1. By team, create a DN strand that is at least 20 nucleotide pairs long with at least one stretch that has the sequence 2. One member should be sketching the DN strand on the sheet provided 3. Indicate the 5 end and the 3 end for each strand
Modelling 4. You are modeling eukaryotic DN. How would prokaryotic DN be different? 5. Use the clay to create helicase, topoisomerase, and single-strand binding proteins. 6. Show how these act in unwinding, stabilizing and holding the strands apart.
Modelling 7. In real life, RN primers are 7-10 nucleotides long. reate two 3-nucleotide long RN primers that would correspond to the sequence complementary strands closest to the two replication forks. 8. reate primase using clay and use it to attach the RN primers to the correct sequences on the complementary DN strand.