"Conservative vs Semi-conservative DNA replication"

• What should you be able to describe by the end of the video on DNA replication?

  How scientists determine that DNA replication is semi-conservative
• Why is the topic of DNA replication considered tricky?

  It involves complex concepts that require careful understanding
• What type of replication mechanism 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
• What is produced at the end of DNA replication?

  Two molecules of DNA from one original molecule
• What does each of the two copies of DNA contain after replication?

  One strand from the original DNA molecule and one new strand
• When was the structure of DNA first discovered?

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

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

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

  Nitrogen 14 and nitrogen 15
• Which nitrogen isotope is the most 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 spun it in a centrifuge
• What does the position of the DNA band in the centrifuge depend on?

  How heavy the DNA is
• What happens to DNA containing nitrogen 14 in the centrifuge?

  It forms a band near the top of the tube
• What happens to DNA containing nitrogen 15 in the centrifuge?

  It forms a band near the bottom of the tube
• What did scientists do after culturing bacteria in nitrogen 15?

  They transferred the bacteria to nitrogen 14
• What was the result after extracting and spinning the DNA from bacteria grown in nitrogen 14?

  It produced a band in between the two bands produced before
• What does the presence of one strand with nitrogen 14 and one strand with nitrogen 15 indicate?

  That DNA replicated semi-conservatively
• What happens when the bacteria replicate one more time on nitrogen 14?

  It produces a bond pattern with an intermediate bond and another bond near the top
• How many DNA molecules are produced after two rounds of replication?

  Four DNA molecules
• What would happen in conservative replication after one round of replication?

  One DNA molecule containing only nitrogen 15 and one containing only nitrogen 14
• What would happen in conservative replication after two rounds of replication?

  One DNA molecule containing only nitrogen 15 and three containing only nitrogen 14
• What would be the bonding pattern in conservative replication?

  No DNA molecules would contain both nitrogen 14 and nitrogen 15
• What is the experiment that demonstrates DNA replication is semi-conservative?

  • Bacteria grown in nitrogen 14 produce lighter DNA.
  • Bacteria grown in nitrogen 15 produce heavier DNA.
  • Transferring bacteria from nitrogen 15 to nitrogen 14 shows intermediate DNA.
  • After two rounds of replication, DNA shows both nitrogen isotopes.
• What are the differences between semi-conservative and conservative replication?

  Semi-conservative replication:

  • Each new DNA molecule has one original and one new strand.
  • Produces intermediate bands in centrifuge.

  
  

  Conservative replication:

  • One DNA molecule has two original strands, another has two new strands.
  • Produces distinct bands without intermediates.