DNAreplicationSemiconservative replicationCopies information from one strand to a new complementary strand·Melt double-stranded DNA? Polymerize new strand complementary to each melted single-strandOriginXParentalstranXINewdaughterstrandsIReplicationforkReplicationfork
DNA replication Semiconservative replication Copies information from one strand to a new complementary strand • Melt double-stranded DNA • Polymerize new strand complementary to each melted single-strand
Replication ForkWhereparental strands separate and new strands synthesizedBeginsatoneOrisiteinbacteriaBegins at numerous sites in eukaryotic cellsParentalstrandsNewstrandsReplicationfork
Replication Fork Where parental strands separate and new strands synthesized Begins at one Ori site in bacteria Begins at numerous sites in eukaryotic cells
Replication Modelslocomotive model of replicationReplication machinery moves along DNA like train on tracksFactory model of replicationReplication machinery is stationary and feeds DNA throughThis is the true modelFluorescentfoci:stationaryDNA synthesis
Replication Models locomotive model of replication Replication machinery moves along DNA like train on tracks Factory model of replication Replication machinery is stationary and feeds DNA through This is the true model
DNAReplicationDNA polymerase synthesizes 5'to 3"Reads3'to 5'3'OH of last nt attacks P of incoming ntBreaks phosphoanhydride bond of dNTP:forms phosphodiester bond in DNAIrreversible due to hydrolysis of PPi (G ~ O). Must have 3'-OH to add ontoPXP. Has proofreading ability
DNA Replication DNA polymerase synthesizes 5’ to 3’ Reads 3’ to 5’ 3’OH of last nt attacks P of incoming nt Breaks phosphoanhydride bond of dNTP; forms phosphodiester bond in DNA Irreversible due to hydrolysis of PPi (ΔG ≈ 0) • Must have 3’-OH to add onto • Has proofreading ability
ObstaclestoDNAPolymeraseCan only extend existing chain needs 3'-OH to build onSolutionUseRNA polymerase (DNA primase) to make RNA primerRemovedlater(noproofreading)TemplateDNAstrandDirectionofchaingrowthRNANewlysynthesizedprimerDNA
Obstacles to DNA Polymerase Can only extend existing chain needs 3’-OH to build on Solution Use RNA polymerase (DNA primase) to make RNA primer Removed later (no proofreading)