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
• When was the structure of DNA first discovered?

  In the 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 did scientists do with the bacteria to study DNA replication?

  They extracted the DNA and centrifuged it
• What does the position of the DNA band in the centrifuge depend on?

  How heavy the DNA is
• Where did the DNA containing nitrogen 14 form a band in the centrifuge?

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

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

  They replicated their DNA once
• What did the DNA extracted after one round of replication show?

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

  It contains one strand of nitrogen 14 and one of nitrogen 15
• What happens when the bacteria replicate their DNA a second time 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 happen after two rounds of conservative replication?

  One molecule would contain nitrogen 15, three nitrogen 14
• What is the process of semi-conservative replication?

  • DNA double helix separates
  • Each strand is replicated
  • Produces two DNA molecules
  • Each molecule has one original and one new strand
• What are the key differences between semi-conservative and conservative replication?

  Semi-conservative replication:

  • Produces DNA with one original and one new strand

  
  

  Conservative replication:

  • Produces one DNA molecule with two original strands
  • Produces another with two new strands
• What experimental method did scientists use to determine DNA replication type?

  1. Extract DNA from bacteria
  2. Centrifuge to separate based on weight
  3. Grow bacteria in different nitrogen isotopes
  4. Analyze band positions in centrifuge
• What are the implications of the banding patterns observed in the experiment?

  • Intermediate band indicates semi-conservative replication
  • Distinct bands indicate conservative replication