DNA
Replication
Preparing for
mitosis or meiosis
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1
Replication Facts
• DNA has to be copied
before a cell divides
• DNA is copied during the S
or synthesis phase of
interphase
• New cells will need identical
DNA strands
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DNA Replication
• Enzyme Helicase unwinds
and separates the 2 DNA
strands by breaking the
weak hydrogen bonds.
• Two strands open forming
Replication Forks (Yshaped region)
5’
3’
Parental DNA Molecule
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3’
Replication
Fork
3
DNA Replication
•
An enzyme called DNA
polymerase grabs new
nucleotides found floating in
the cell and adds the new
complimentary nucleotides to
the single DNA Strand.
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DNA Replication
• As the new nucleotides are
attached Covalent bonds form
between the sugar of one
nucleotide and the phosphate of
the other nucleotide.
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DNA Replication
• Because each DNA strand is so
long replication does not happen
in just one location of he
Chromosome.
• Multiple bubble of polymerase
will be adding new bases at the
same time. Once done the
polymerase falls off.
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DNA Replication
• In each new DNA strand one
side of the double helix is the
original molecule and the other
side is the new strand.
• This is called Semi-Conservative
replication.
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Replication of Strands
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Proofreading New DNA
• DNA polymerase initially makes
about 1 in 10,000 base pairing
errors
• Enzymes proofread and correct
these mistakes
• The new error rate for DNA that
has been proofread is 1 in 1 billion
base pairing errors
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9
Question:
• What would be the
complementary DNA
strand for the following
DNA sequence?
CGTATG
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