dna replication. watson and crick noticed the huge benefit of double strands each strand can serve...
DESCRIPTION
DNA Replication Prior to mitosis and meiosis DNA must be copied Like cells, all DNA comes from previously existing DNATRANSCRIPT
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DNA Replication
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DNA Replication
Watson and Crick noticed the huge benefit of double strands
Each strand can serve as a template for making for making the other
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DNA Replication
•Prior to mitosis and meiosis DNA must be copied•Like cells, all DNA comes from previously existing DNA
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Semiconservative Model Each strand serves
as a template for the creation of a new strand of DNA
2 DNA molecules are created, each containing 1 strand of the original DNA
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Semiconservative Replication
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The Beginning
•Topoisomerase unwinds the helix•Helicase separates the strands•Single stranded binding proteins (SSBs) keep the strands separated
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Topoisomerase, Helicase and Single-Strand Binding Protein
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Priming DNA
A short RNA primer is added first by primase
DNA can only be added to an existing primer
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DNA Polymerases
Each nucleotide is added one by one by DNA polymerases
A added to T
G added to C etc.
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Antiparallel DNA StrandsThe two strands are arranged in opposite directions
Each strand has an “end”
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The Leading Strand
Built continuously as the replication fork opens in front of it
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The Lagging Strand
•Built in pieces the opposite direction of replication•Built in fragments, called Okazaki fragments
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Review Helicase separates strands, SSBs help keep
strands apart DNA polymerase adds nucleotides DNA ligase fuses Okazaki fragments of lagging
strands together
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Topoisomerase
Helicase Single Stranded Binding Proteins
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Primase
3’
5’
DNA Polymerase
Leading Strand
Lagging StrandOkazaki Fragments
DNA Ligase