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Happy Hump Day!
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Who gets Doughnuts
ClassGrowth 5% 3.55% 1.9% - 0.45% -2%
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OverviewThe nucleus during Interphase:
-nuclear membrane separates fluid of nucleus from cytoplasm
-DNA is in form of chromatin (not densely coiled into chromosomes)
-enzymes are present: helicase, polymerase, ligase, primase, gyrase
-free nucleotides are present (technically called nucleoside triphosphates)
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DNA Replication 7.2
• DNA replication occurs in a 5’ to 3’ direction–5’ end of the free DNA nucleotide is
added to the 3’ end of the chain of nucleotides which is already synthesized
• Replication begins at a particular sequence of nucleotides called the origins of replication
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7.2– in eukaryotic
chromosomes, replication can be initiated at several different points depending on what gene or genes need to expressed, while in prokaryotes the entire genome is replicated at once
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7.2.2• It is at these points that a special enzyme called
helicase splits the DNA into its two antiparallel strands
• Another enzyme DNA gyrase is inserted in the helix to relieve strain from the coil
• On the strand running in the 3'--->5' direction (called the leading strand), another enzyme called DNA polymerase III latches on at one end of the opening, called the replication bubble
• DNA Polymerase III begins to continuously lay a new DNA strand from free nucleotides in the nucleus( Lay 5’-3’)
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7.2.2• At the same time DNA polymerase III is laying
new DNA, helicase is continuing to split the strands, thus allowing replication to continue uninterrupted
• On the opposite strand running 5'--->3‘ (called the lagging strand), replication is not so simple
• Because new strands have to be laid in the 5'---3' direction, DNA polymerase III cannot lay continuously as it can on the other strand.
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7.2.2
• Instead, RNA primase lays short segments of RNA primer nucleotides at many points along the strand
• When one segment of primer comes in contact with another, DNA polymerase I attaches and replaces the primer with DNA.
• These segments of DNA are called Okazaki fragments
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• Once the Okazaki fragments have been laid, they are joined by yet another enzyme known as DNA ligase
• DNA ligase attaches DNA into the gaps between fragments and completes the new strand.
http://nobelprize.org/educational_games/medicine/dna/a/replication/replication_ani.html
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·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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DNA 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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animation
further reading on experiments to confirm semiconservative replication: p 250-251