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DNA Replication

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DNA Replication Replication and cell division All DNA must be copied before cell division (mitosis) so each daughter cell can receive a complete set. – PowerPoint PPT presentation

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Title: DNA Replication


1
DNA Replication
2
Replication and cell division
  • All DNA must be copied before cell division
    (mitosis) so each daughter cell can receive a
    complete set.
  • DNA replication occurs during the S phase of the
    cell cycle, before chromatin condenses into
    chromosomes.

http//ghr.nlm.nih.gov/handbook/illustrations/chro
mosomestructure.jpg
3
(No Transcript)
4
3 main steps to replication
  • Step 1 Helicase unzips the DNA strand by
    breaking the hydrogen bonds between base pairs
    creates two new template strands
  • Step 2 DNA polymerase inserts new complementary
    bases (and builds P/S backbone)
  • Step 3 DNA polymerase proofreads the sequence
    fixes errors

5
Antiparallel strands of DNA
  • Notice that one strand is always upside-down
    relative to the other strand?
  • The two strands are antiparallel to each other

6
Direction of replication
  • One DNA strand forms in the same direction that
    helicase unzips it
  • The other one must go the other way (because DNA
    is antiparallel)
  • This causes fragments of DNA to form, which are
    then later sealed by another enzyme

YouTube DNA Replication Process
7
The result of replication is
  • two new strands of DNA that are exactly the same
    as the original strand

8
Why is DNA called semi-conservative?
  • DNA replication is called semi-conservative
    because each strand has an old part and a new
    part
  • Semi half or part conservative preserving
    the old ways

9
DNA replication is very accurate
  • DNA polymerase laying down new nucleotides makes1
    error per 1,000,000 nucleotides
  • Sounds good?
  • 3,000,000,000 base pairs in the each human
    cell3,000 possible errors each time our cells
    replicate
  • BUTafter DNA Polymerase is done, other enzymes
    proofread and correct the new strand
  • Afterward, the error rate is about 1 error per
    10,000,000,000 or 1 error every 3 cell divisions.

10
Base pairing practice
  • For each example below, give the correct
    complementary strand of DNA.
  • T T G C T A G
  • A A C G A T C
  • T A G C G C T
  • A T C G C G A
  • A C C G T C A
  • T G G C A G T
  • G C T A T G T
  • C G A T A C A

11
Replication practice
T G C A G A T
T G C A G A T
new strands
old strands
DNA polymerase
new strands
old strands
DNA polymerase
helicase
A C G T C T
A C G T C T
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