TOPIC 1B- DNA REPLICATION

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ROLE OF DNA HELICASE
Unwinds DNA and breaks hydrogen bonds between bases.
so nucleotides attach
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ROLE OF DNA POLYMERASE
Joins adjacent nucleotides,
forms phosphodiester bonds,
makes polymer DNA from nucleotides
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PROCEDURE BEFORE CELL DIVISION
DNA copies itself so each new cell has full amount of DNA
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DNA REPLICATION STEP 1-3
1. representative portion of DNA undergoes replication
2. DNA helicase separates the 2 strands of DNA by breaking hydrogen bonds between complementary base pairs
3. DNA helicase completes splitting of strands- acts as a template, free activates nucleotide
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DNA REPLICATION STEP 4-5
4. Activated nucleotides joined by DNA polymerase making phosphodiester bonds, remaining unpaired bases continue to attract
5. All nucleotides joined- it forms polynucleotide chain using DNA polymerase
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WHAT DOES DNA REPLICATION FORM?
2 identical strands of DNA, each strand remains half of original DNA material
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WHAT REACTION JOINS NUCLEOTIDES AND WHAT ENZYME?
DNA polymerase joins nucleotides together in a condensation reaction
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MUTATIONS IN DNA REPLICATION
Extra base may be inserted or deleted- DNA polymerase corrects errors in replication process
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DIRECTIONALITY OF DNA
The double helix strands of DNA run antiparallel to each other,
new DNA is always made in 5' to 3' direction because DNA polymerase only works in 3' to 5' direction
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DNA POLYMERASE 3' TO 5' END
DNA polymerase is complementary to the active site of the 3' end therefore the enzyme can only add new nucleotides at the 3' end, it moves down template strand in 3' to 5' direction because strands are antiparallel and DNA polymerase working on one templa
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WHAT IS AT THE 5' AND 3'
5' phosphate group,
3' hydroxyl group
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MESELSON AND STAHL EXPERIMENT
They used two isotopes of Nitrogen- heavy nitrogen (15) and light nitrogen (14)
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MESELSON AND STAHL EXPERIMENT METHOD
2 samples of bacteria were grown, one in nutrient broth containing light nitrogen and one in heavy nitrogen, bacteria reproduced and took nitrogen from broth to make nucleotides for new DNA- nitrogen become part of bacteria's new DNA
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MESELSON AND STAHL EXPERIMENT METHOD 2
Sample of DNA taken from each batch and spun in centrifuge,
DNA from heavy nitrogen settled lower in centrifuge tube than DNA in light nitrogen
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MESELSON AND STAHL EXPERIMENT METHOD 3
Bacteria grown in heavy nitrogen broth were taken out and put in broth with only light nitrogen, it was left for one round of DNA replication and another DNA sample was taken out and spun in centrifuge
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CONSERVATIVE REPLICATION OUTCOME
If it was conservative, original heavy DNA would settle at the bottom and new light DNA would settle at the top
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SEMI-CONSERVATIVE REPLICATION OUTCOME
The new bacterial DNA would contain one strand of old DNA with heavy nitrogen and one new strand containing DNA with light nitrogen,
DNA would settle between light nitrogen and heavy nitrogen
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RESULTS OF THE MESELSON AND STAHL EXPERIMENT
The DNA settled in the middle therefore the DNA molecules contained both heavy and light nitrogen- it replicated semi-conservatively in the light nitrogen
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Other cards in this set

Card 2

Front

ROLE OF DNA POLYMERASE

Back

Joins adjacent nucleotides,
forms phosphodiester bonds,
makes polymer DNA from nucleotides

Card 3

Front

PROCEDURE BEFORE CELL DIVISION

Back

Preview of the front of card 3

Card 4

Front

DNA REPLICATION STEP 1-3

Back

Preview of the front of card 4

Card 5

Front

DNA REPLICATION STEP 4-5

Back

Preview of the front of card 5
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