BBMB 405 1st Edition Lecture 24 Outline of Last Lecture XIV Chapter 28 DNA Replication Repair and Recombination A Introduction Central Dogma and Review B DNA replication proceeds by polymerization of deoxyribonucleoside triphosphates along template Outline of Current Lecture XIV Chapter 28 DNA Replication Repair and Recombination B DNA replication proceeds by polymerization of deoxyribonucleoside triphosphates along template C DNA unwinding and supercoiling are controlled by topoisomerases D DNA replication is highly coordinated Current Lecture XIV Chapter 28 DNA Replication Repair and Recombination B DNA replication proceeds by polymerization of deoxyribonucleoside triphosphates along template 1 Replication occurs at replication forks a DNA only synthesized in 5 to 3 direction b RNA makes DNA primer c Leading strands initially unwound makes continuous strand d Okazaki fragments semi discontinuous replication of lagging strand These 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 e Lagging strand fragments needs to be initiated separately f 2 DNA synthesis is initiated by a primer a RNA primers are synthesized by primase RNA doesn t require a primer b Lagging strand synthesis initiation occurs more frequently than leading strand initiation c 3 Multiple replicative polymerases Added line Between DNA polymerase beta and delta DNA polymerase epsilon primary enzyme of DNA synthesis leading more tightly bound DNA polymerase delta lagging strand dissociates quickly 4 DNA ligase joins Okazaki fragments a RNA ends of fragments replaced with DNA by DNA polymerase b DNA ligase joins the gaps between the fragments c Monophosphate at end so need to put in energy for reaction to occur d 5 How is DNA unwound at replication fork 6 Helicase separates DNA strands at replication fork converts energy into chemical work 2 ATP per base pair 7 Single stranded binding SSB protein prevents unwound strands from reannealing coats single strand until primer can get there C DNA unwinding and supercoiling are controlled by topoisomerases 1 Topolgy mathematical study of shapes and topological spaces properties of space that is preserved under continuous deformations including stretching and bending 2 Lk Tw Wr Straight from slide a Linking number Lk Number of times one strand winds about the other independent of superhelical DNA conformation b Twist Tw Number of times one strand winds about the duplex axis in the particular conformation of interest c Writhing number Wr Number of turns that the duplex axis makes about the superhelix axis in conformation of interest d 3 What enzyme can change the topology of DNA molecule topoisomerases work before replication fork a DNA topoisomerase I relax supercoiled structures change Lk number use tyrosine b DNA topoisomerase II introduce negative supercoils removes tangles Green ATP binding N gate Thick yellow DNA cleavage and ligase DNA gate Thin yellow C gate c Chemotherapeutics Top two inhibitors block DNA or ATP from binding to topoisomerase II Top two poisons block regulation of DNA kill turn over and break DNA d Target of Antibiotics broad spectrum antibiotics used for hospital acquired infections inhibit topoisomerase II ligase domain selectively D DNA replication is highly coordinated 1 Sliding clamp improves speed and processivity of DNA polymerase 2 Sliding clamp loader ATP dependent binding to clamp when open then binds clamp to DNA then hydrolysis releases clamp loader 3 Holoenzyme a b Gray epsilon proofreading c Orange theta stimulate proofreading d Orange Yellow Beta 2 sliding clamp e Purple phi and blue x SSB interacting f Properties fast high rates of catalysis processive doesn t fall off substrate low abundance high fidelity composed of many subunits
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