1.2.10 DNA replication

Question 1

What must be produced when a cell divides?

Answer 1

When a cell divides, an exact copy of the DNA must be produced

Question 2

What is the first step of DNA replication?

Answer 2

The double helix unwinds from one end to the other, breaking the H-bonds

Question 3

What happens in DNA replication after the two strands have split?

Answer 3

Free nucleotides line up along each strand of DNA

Question 4

What enzyme bonds the new DNA nucleotides?

Answer 4

The DNA-polymerase enzyme binds the new DNA nucleotides

Question 5

What is the name given to DNA replication?

Answer 5

Semi-conservative replication. This is because half of the original DNA strand is conserved in each of the new DNA molecules

Question 6

What was the experiment carried out by Meselson and Stahl?

Answer 6

• Used DNA from E-coli, grown in N15
  
  • All the nucleotides contained heavy nitrogen
  • DNA was very dense
• They moved this DNA into N14
  
  • All new nucleotides were light, but originals were heavy
• They allowed the bacteria to divide and replicate once
  
  • The DNA was extracted and centrifuged
  • Heavy DNA at the bottom, light at the top
• The result was a single band in the middle
• No heavy DNA remained, meaning they could rule out conservative replication
• They then let the DNA replicate again
  
  • This resulted in one medium and one light band
  • This ruled out fragmentary replication