1 DNA Replication copyright cmassengale Vyi4.

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DNA DNA ReplicatiReplicati

onon

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http://www.youtube.com/watch?v=9u4Zo7UVyi4



What is replication?

• The process of making an EXACT copy of DNA.

• Why does the copy need to be EXACT?

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When does When does replication occur?replication occur?

• DNA has to be copied DNA has to be copied before a cell dividesbefore a cell divides

• New cells will need New cells will need identical identical DNA strandsDNA strands

• When do you need new When do you need new cells? Growth, healing, cells? Growth, healing, making sex cells…making sex cells…


Replication video

• http://www.youtube.com/watch?v=4jtmOZaIvS0&feature=related


http://www.youtube.com/watch?v=4jtmOZaIvS0&feature=related



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DNA ReplicationDNA Replication• HelicaseHelicase (a protein called (a protein called

an ENZYME) unwinds and an ENZYME) unwinds and separates the 2 DNA separates the 2 DNA strands by breaking the strands by breaking the weak hydrogen bondsweak hydrogen bonds

• Single-Strand Binding Single-Strand Binding ProteinsProteins attach and keep the 2 DNA strands separated and untwisted


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DNA ReplicationDNA Replication• DNA polymerase can then

add the new nucleotides• What chemical reaction is

this?


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Proofreading New Proofreading New DNADNA

• DNA polymerase initially DNA polymerase initially makes about makes about 1 in 10,0001 in 10,000 base base pairing errors (MUTATIONS)pairing errors (MUTATIONS)

• If you have about 3 billion If you have about 3 billion base pairs, how many errors is base pairs, how many errors is this? this?


Telephone – the written version

• One side of the room versus the other.

• You need a scrap piece of paper and something to write with.


DNA polymerase

• proofreads and correct proofreads and correct these mistakesthese mistakes

• The new error rate for The new error rate for DNA that has been DNA that has been proofread is proofread is 1 in 1 billion1 in 1 billion base pairing errorsbase pairing errors

• Much better!!!Much better!!!


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Semiconservative Model Semiconservative Model of Replicationof Replication

• Idea presented by Idea presented by Watson & CrickWatson & Crick• 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

Parental DNA

DNA Template

New 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

• Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA

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


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Question:Question:

•What would be the complementary DNA strand for the following DNA sequence?

DNA 5’-CGTATG-3’DNA 5’-CGTATG-3’copyright cmassengale

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Answer:Answer:

DNA 5’-CGTATG-3’DNA 5’-CGTATG-3’

DNA 3’-GCATAC-5’DNA 3’-GCATAC-5’


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1 DNA Replication copyright cmassengale Vyi4.

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