3.4.1 dna replication 3.4 · 3.4notes_dnareplication.notebook 1 october 02, 2012 nov 59:03 am dna...
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3.4Notes_DNAReplication.notebook
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DNA Replication3.4
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3.4.1• During Interphase, DNA must be replicated so that mitosis can generate two daughter cells that will each have an identical copy
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3.4.1• The nucleus during Interphase:
nuclear membrane separates fluid of nucleus from cytoplasmDNA is in form of chromatin (not densely coiled into chromosomes)enzymes are present: helicase, polymerase, ligase, primasefree nucleotides are present (technically called nucleoside triphosphates)
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3.4.1• General steps of DNA replication:
1) an enzyme called helicase unwinds and separates the strands of the DNA molecule.
breaks the hydrogen bonds between bases forms the replication "bubble" or "fork"
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3.4.12) Singlestranded binding proteins or helixdestabilizing proteins
keep two strands of DNA molecule apart.
3) RNA primase: an enzyme that synthesizes a short RNA primer on the DNA
4) DNA polymerase III: starts at the RNA primer and catalyzes the addition of free nucleotides to DNA strand.
only work in the 5' to 3' direction (of the new strand) proof reads the DNA
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3.4.1
psst: use the magic pen!!
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3.4.14) continued:
Leading Strand: a DNA polymerase III enzyme moves toward the replication fork adding nucleotides to the 3' to 5' parent strand (creating the 5' to 3' new strand)
= continuous
Lagging Strand: DNA polymerase III moves away from the replication fork on the 5' to 3' parent strand creating pieces called Okazaki fragments.
= discontinuous
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3.4.1
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3.4.15) DNA polymerase I: removes RNA primer and replaces it with nucleotides (DNA)
6) DNA ligase: joins fragments of DNA with sugarphosphate bonds
between Okazaki fragments on lagging strand where RNA primer was removed
animation
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3.4.2• Complimentary base pairing rules are used
A bonds with T C bonds with G
• This ensures the correct base is incorporated into the new DNA strand conservation of the base sequence the newly formed strand is identical to the old strand it is replacing
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3.4.2
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3.4.3DNA replication is semiconservative.• the 2 strands of the original molecule are each used as a template for the formation of the new strands.• The result is two newly formed strands that each consist of one old strand and one new strand
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3.4.3This is opposed to old theories:
• Conservative replication = one completely new double helix is formed and the old is preserved• Dispersive replication = the new double helix and the old are randomly mixed together
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3.4.3animation
further reading on experiments to confirm semiconservative replication: p 250-251
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Follow up activity:• CP Biology text:
Read pages 333335 Answer the Assessment questions 15 on a separate sheet of paper
*write the question OR answer in complete sentences.
• IB Biology text: Read p 252255 "DNA replication is complex and has several unique features" add information to your notes
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