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DNA ReplicationDNA Replication

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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

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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

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DNA Damage & DNA Damage & RepairRepair

• Chemicals & ultraviolet radiation damage the DNA in our body cells

• Cells must continuously repair DAMAGED DNA

• DNA ligase and DNA polymerase replace and bond the new nucleotides together

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