DNA replication

• What is the role of key enzymes in DNA replication?

  They facilitate the replication process
• What is the structure of DNA?

  A double-stranded molecule of nucleotides
• How are the two strands of DNA held together?

  By hydrogen bonds between the bases
• Which bases pair together in DNA?

  Guanine with cytosine, adenine with thymine
• What is complementary base pairing?

  Specific pairing of DNA bases
• What shape does DNA form?

  A double helix
• What happens during DNA replication?

  All DNA is copied before cell division
• What is the first stage of DNA replication?

  DNA helicase attaches to the DNA molecule
• What does DNA helicase do?

  Breaks hydrogen bonds between complementary bases
• What are the three nucleotides lined up with during replication?

  Complementary bases on the DNA strands
• What are activated nucleotides?

  Nucleotides with three phosphate groups
• Why are activated nucleotides important?

  They provide energy for the reaction
• What type of reaction occurs when phosphodiester bonds form?

  A condensation reaction
• What is semi-conservative replication?

  Each DNA molecule has one original strand
• What is a mutation?

  A change in the DNA sequence
• How do mutations occur?

  They are random and spontaneous
• What direction does DNA polymerase copy DNA?

  From the 5' end to the 3' end
• How does DNA polymerase behave on the two strands during replication?

  One strand is continuous, the other is shorter
• What are the stages of DNA replication?

  1. DNA helicase attaches and unwinds DNA
  2. Nucleotides line up with complementary bases
  3. DNA polymerase forms phosphodiester bonds
  4. DNA ligase joins shorter strands
• What are the key enzymes involved in DNA replication and their roles?

  • DNA helicase: Unwinds DNA and breaks hydrogen bonds
  • DNA polymerase: Synthesizes new DNA strands
  • DNA ligase: Joins shorter DNA fragments together
• 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 semi-conservative replication?

  Two molecules of DNA
• What does each copy of DNA contain after semi-conservative replication?

  One strand from the original DNA
• When was the structure of DNA first discovered?

  In the 1950s
• What was one possibility for DNA replication that scientists considered?

  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 spun in a centrifuge?

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

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

  Near the bottom of the tube
• What did scientists do after growing bacteria in nitrogen 15?

  Transferred them to nitrogen 14
• What was the result after one round of replication in nitrogen 14?

  DNA formed 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 after the bacteria replicate one more time on nitrogen 14?

  Another bond forms near the top of the tube
• 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 would contain nitrogen 14
• What bonding pattern would indicate conservative replication?

  No DNA molecules would contain both isotopes