DNA
Replication
http://www.youtube.com/watch?v=9u4Zo7U
Vyi4
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What is replication?
• The process of making an
EXACT copy of DNA.
• Why does the copy need to be
EXACT?
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When does
replication occur?
• DNA has to be copied
before a cell divides
• New cells will need identical
DNA strands
• When do you need new
cells? Growth, healing,
making sex cells…
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Replication video
• http://www.youtube.com/watch?
v=4jtmOZaIvS0&feature=related
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DNA Replication
• Helicase (a protein called
an ENZYME) unwinds and
separates the 2 DNA
strands by breaking the
weak hydrogen bonds
• Single-Strand Binding
Proteins attach and keep
the 2 DNA strands
separated and untwisted
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DNA Replication
•
•
DNA polymerase can then add
the new nucleotides
What chemical reaction is this?
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Proofreading New DNA
• DNA polymerase initially makes
about 1 in 10,000 base pairing
errors (MUTATIONS)
• If you have about 3 billion base
pairs, how many errors is this?
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Telephone – the
written version
• One side of the room versus the
other.
• You need a scrap piece of paper
and something to write with.
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DNA polymerase
• proofreads and correct these
mistakes
• The new error rate for DNA
that has been proofread is 1
in 1 billion base pairing
errors
• Much better!!!
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Semiconservative Model of
Replication
• Idea presented by Watson & Crick
• The two strands of the parental
molecule separate, and each acts as a
template for a new complementary
strand
• New DNA consists of 1
PARENTAL (original) and 1 NEW
DNA Template
strand of DNA
Parental DNA
New DNA
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DNA Damage & Repair
• Chemicals & ultraviolet radiation
damage the DNA in our body cells
• Cells must continuously repair
DAMAGED DNA
• Excision repair occurs when any of
over 50 repair enzymes remove
damaged parts of DNA
• DNA polymerase and DNA ligase
replace and bond the new nucleotides
together
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<3
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Question:
• What would be the
complementary DNA
strand for the following
DNA sequence?
DNA 5’-CGTATG-3’
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Answer:
DNA 5’-CGTATG-3’
DNA 3’-GCATAC-5’
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