Eukaryotic Cell Division

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Eukaryotic Cell Division

• A DNA Replication Process

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What Are the Important Features of DNA?
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What Are the Important Features of DNA?
Ribose-Phosphate Backbone
5- Carbon
Purines (A G)
If an additional nitrogenous base was added to
this DNA how/where would the base attach?
Pyrimidines (C T)
3- Carbon
Ribose
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Incorporation of a New Base
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The Other Half of the Story
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Hydrogen Bonding in DNA
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Antiparallel Strands of DNA

• 5TGCTGACTG3
• 3ACGACTGAC5

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DNA is Protein Bound
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How Does the Cell Replicate Its DNA?

• When, in the cell cycle, is the DNA replicated?

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The Cell Cycle
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Interphase

• Interphase often accounts for 90 of the cell
  cycle and can be subdivided into three subphases.
• G1 PhasePrimary growth phase
• S Phase DNA synthesis
• G2 phase Organelle replication and chromosome
  condensation

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Interphase

• Interphase often accounts for 90 of the cell
  cycle and can be subdivided into three subphases.
• G1 PhasePrimary growth phase
• S Phase DNA synthesis
• G2 phase Organelle replication and chromosome
  condensation

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Who can find the mistake?
Figure 16.7 A model for DNA replication the
basic concept
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An Extremely Important Point

• DNA Replication MUST Occur in the 5 to 3
  direction

5TGCTGACTG3 3 ACT 5
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An Extremely Important Point

• DNA Replication MUST Occur in the 5 to 3
  direction

5TGCTGACTG3 3 GACT 5
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An Extremely Important Point

• DNA Replication MUST Occur in the 5 to 3
  direction

5TGCTGACTG3 3 CGACT 5
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An Extremely Important Point

• DNA Replication MUST Occur in the 5 to 3
  direction

5TGCTGACTG3 3ACGACT 5
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Synthesis of DNA
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DNA Replication Starts at Origins of
Replication (ORI)
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Synthesis of leading (5 to 3) and lagging (3
to 5) strands during DNA replication
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Summary
Helicase
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The main proteins of DNA replication and their
functions
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Integrity of the Genome

• Mistakes can be made
• Error rate 110,000 base pairs
• DNA polymerase has proof reading function
• Nucleotide excision repair
• The ends of the chromosomes become ragged
• Repeated replication leads to shortening of the
  chromosomes
• Telomerase

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Nucleotide Excision Repair

• Xeroderma pigmentosum
• Inherited defect in nucleotide excision repair
• Increased chance of getting skin cancer

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Telomerase

• Cancer cells overexpress telomerase.
• This contributes to the extended lifespan of
  cancer cells

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Telomerase In Action