DNA Replication and Repair
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During cell division nucleus is divided _________________
Cytokinesis
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Cell is split into two cells, each daughter cell has an ____________copy of the parent’s cells
__________
Each DNA strand acts as a ______________to build the complementary strand
______________ bonds between complementary bases break and DNA ___________
DNA Replicates Semi-conservatively
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Each DNA molecule is composed of one _________strand and one
_______________________strand
Meselson & Stahl
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Experimented with ______________(bacteria)
Grew E. coli in _____________medium rich in________
Bacteria reproduced ________ generations
Same bacteria is ____________to nutrient medium containing ________
M & S devised a new centrifugation method to measure __________________before and
after switch to light N
Experiment
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Samples of DNA were ________________in a solution of cesium chloride, for many hours
at high speeds
____________________stops once the DNA reaches the same density in the gradient as its
own
M & S hypothesized that DNA strand of_______________, therefore
______________________density
Process of DNA Replication
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Step 1: ________________the DNA Strands
Begins when ____________at a specific site on DNA
__________________unwinds the double helix by breaking the hydrogen bonds between
bases
Strands have a natural tendency to ___________- pairing of bases
Single Stranded Binding Proteins
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SSB’s bind to the ________________single strands and block H bonding
______________: enzyme that relieves any tension brought about by the unwinding of DNA
in bacteria
DNA cannot be _______________because of its large size
Replication Fork
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The replication fork is the __________ where the DNA strands are still joined.
When two replication forks are quite near each other a ______________________forms (See
figure 4 page 220)
Eukaryotes
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In eukaryotes there are ________________of replication forks, eventually bubbles become
______________and two new double-stranded daughter molecules are completely formed
Building the Complementary Strands
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_______________________enzyme responsible for synthesizing complementary strands of
DNA during DNA replication in prokaryotes
________complementary nucleotides in the ______ direction using RNA primers as starting
points
RNA Primer
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RNA Primer is a sequence of __________________which is annealed to the template
because DNA polymerase III ____________________a complementary strand by itself
Primase
 Primase is the enzyme that ____________________.
 RNA primer is ________________once DNA polymerase III starts elongation
 Deoxyribonucleoside triphosphates are added, the _____________obtained from breaking
the bond between the P’s __________a complementary nucleotide to the elongating strand
Direction
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DNA is always synthesized in the _________direction
Therefore __________strand can be built continuously
__________________- 5’ to 3’ direction - is built towards replication fork
Lagging Strand
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The lagging strand is the strand tht is synthesized in _______fragments - known as
___________ fragments
__________________is an enzyme that removes RNA primers and replaces them with the
appropriate deoxyribonucleosides
______________- joins the Okazaki fragments
See figure 7 page 221
Quality Control
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_______ DNA polymerase III and DNA polymerase I act as quality control checkers (search
for _________)
If error is detected either can act as an ___________
This enzyme backtracks and __________the incorrect nucleotide
Review
1. How does the DNA strand unzip?
2. What does it mean when we say DNA replicates semi-conservatively?
3. How did Meselson & Stahl demonstrate this semi-conservative form of replication?
4. What is the name of the enzyme that unwinds the double helix?
5. What keeps the individual strands from annealing to each other?
6. What is the name of the enzyme that relieves any tension brought about by the unwinding of
DNA?
7. What is a replication fork?
8. What is the name of the enzyme responsible for synthesizing strands of DNA during DNA
replication?
9. In what direction does this enzyme add nucleotides?
10. What is a RNA primer?
11. What happens to RNA primer once DNA polymerase III starts elongation?
12. What is the difference between the leading strand and lagging strand?
13. What are the short fragments in the lagging strand called?
14. What enzyme joins the Okazaki fragments together?
15. How does the cell ensure that it has made DNA with the nucleotides in the correct sequence?