DNA Replication

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DNA Replication
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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 why?

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DNA Replication Step 1

• Parent DNA prepares to replicate
• Appears normal

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DNA Replication Step 2

• Enzyme Helicase unzips the DNA strand
• Breaks the weak hydrogen bonds

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DNA Replication Step 3

• Two strands open forming Replication Fork
  (Y-shaped region)

Replication fork
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DNA Replication Step 4
Helicase

• DNA polymerase enzyme adds the new nucleotides
• Enzyme proofreads and corrects mistakes
• DNA polymerase initially makes about 1 in 10,000
  base pairing errors
• The new error rate for DNA that has been
  proofread is 1 in 1 billion base pairing errors

Polymerase
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DNA Replication Step 5

• Replication is complete!
• Result is 2 DNA molecules

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Semiconservative Model of Replication

• 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 strand of DNA

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Question

• What would be the complementary DNA strand for
  the following DNA sequence?
• DNA -CGTATG-

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Answer

• DNA -GCGTATG-