Conservative vs Semi-conservative DNA replication

• What type of replication do scientists call DNA replication?

  Semi-conservative replication
• What happens to the DNA double helix during semi-conservative replication?

  It separates into two polynucleotide strands
• How many molecules of DNA are produced at the end of replication?

  Two molecules of DNA
• What does each of the two copies of DNA contain after replication?

  One strand from the original and one new strand
• In what decade was the structure of DNA first discovered?

  1950s
• What were the two possibilities for DNA replication proposed by scientists?

  Semi-conservative and conservative replication
• What element do all bases in DNA contain?

  Nitrogen
• What are the two main forms of nitrogen isotopes?

  Nitrogen 14 and nitrogen 15
• Which nitrogen isotope is more common?

  Nitrogen 14
• How do nitrogen 15 atoms compare to nitrogen 14 atoms?

  Nitrogen 15 atoms are slightly heavier
• What happens to DNA when it is spun in a centrifuge?

  It forms a band based on weight
• Where does DNA containing nitrogen 14 form a bond in the centrifuge?

  Near the top of the tube
• Where does DNA containing nitrogen 15 form a bond in the centrifuge?

  Near the bottom of the tube
• What happens when bacteria grown on nitrogen 15 are transferred to nitrogen 14?

  They replicate their DNA once
• What did the scientists find after extracting and spinning the DNA from bacteria grown on nitrogen 14?

  It produced a bond in between the two bands
• What does the intermediate bond indicate about the DNA strands?

  It contains one strand of nitrogen 14 and one of nitrogen 15
• What happens when the bacteria replicate again on nitrogen 14?

  It produces a bond pattern with two bands
• How would the results differ if DNA replicated conservatively?

  One molecule would contain only nitrogen 15
• What would be the bonding pattern after two rounds of conservative replication?

  One nitrogen 15 and three nitrogen 14 molecules
• What are the key steps in the experiment to determine DNA replication type?

  1. Grow bacteria in nitrogen 14.
  2. Extract DNA and centrifuge.
  3. Grow bacteria in nitrogen 15.
  4. Extract DNA and centrifuge.
  5. Transfer to nitrogen 14 and replicate once.
  6. Extract DNA and centrifuge.
  7. Analyze bond patterns.
• What are the implications of the bond patterns observed in the experiment?

  • Indicates semi-conservative replication.
  • Shows presence of both nitrogen isotopes.
  • Confirms original and new strand combination.