1 DNA Replication. 2 Video 3 Replication Facts DNA has to be copied before a cell dividesDNA has to...
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Transcript of 1 DNA Replication. 2 Video 3 Replication Facts DNA has to be copied before a cell dividesDNA has to...
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DNA Replication Video
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Replication FactsReplication Facts
• DNA has to be DNA has to be copiedcopied before a cell before a cell dividesdivides
• DNA is copied during DNA is copied during the the SS or synthesis phase or synthesis phase of interphaseof interphase
• New cells will need New cells will need identicalidentical DNA strands DNA strands
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First Steps of First Steps of ReplicationReplication
• Begins at Begins at Origins of ReplicationOrigins of Replication• Two strands open forming Two strands open forming
Replication Replication ForksForks (Y-shaped (Y-shaped region)region)
• NewNew strands grow at the forks strands grow at the forks
ReplicationReplicationForkFork
Parental DNA MoleculeParental DNA Molecule
3’
5’
3’
5’
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Separating DNASeparating DNA
• Enzyme Enzyme HelicaseHelicase unwinds and separates unwinds and separates the 2 DNA strands by the 2 DNA strands by breakingbreaking the weak the weak hydrogenhydrogen bonds bonds
• Single-Strand Binding Single-Strand Binding ProteinsProteins attach and keep the 2 DNA strands separated and untwisted
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Adding on Adding on NucleotidesNucleotides
• BeforeBefore new DNA strands can form, there must be RNA RNA primersprimers present to start the addition of new nucleotides
• PrimasePrimase is the enzyme that synthesizes the RNA Primer
• DNA polymerase can then add on freely floating new nucleotides
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Proofreading New Proofreading New DNADNA
• DNA polymerase initially DNA polymerase initially makes about 1 in makes about 1 in 10,00010,000 base base pairing errorspairing errors
• Enzymes Enzymes proofreadproofread and and correctcorrect these mistakes these mistakes
• The new error rate for DNA The new error rate for DNA that has been proofread is 1 that has been proofread is 1 in 1 in 1 billionbillion base pairing errors base pairing errors
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Semiconservative Model Semiconservative Model of Replicationof Replication
• Idea presented by Idea presented by WatsonWatson & & CrickCrick
• TheThe two strands of the parental molecule separate, and each acts as a template for a new complementary strand
• New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA