3.1.5.2 DNA replication

Question 1

The process of semi-conservative replication

Answer 1

• double helix unwinds
  -strands unzip
  -hydrogen bonds break between complementary bases in the polynucleotide strands
  └using DNA helicase
  -both strands act as a template
  -free DNA nucleotides align
  -complimentary base pairing occurs
• C to G (3 H bonds) and T to A (2 H bonds)
• hydrogen bonds reform
  └DNA polymerase joins adjacent nucleotides in the condensation reaction
  └DNA polymerase is an enzyme so its active site is specific and can only bind to 1 end (=5’ to 3’ direction)
• sugar-phosphate back bone forms
  └using phosphodiester bonds

Question 2

Role of DNA helicase in semi-conservative replication of DNA

Answer 2

unwinds DNA and breaks its hydrogen bonds

Question 3

Role of DNA polymerase in semi-conservative replication of DNA

Answer 3

joins adjacent nucleotides in the condensation reaction

Question 4

What is the experiment that proved semi-conservative replication?

Answer 4

Meselson and Stahl

1. 2 samples of bacteria grown, one in sample containing light nitrogen and one containing heavy nitrogen
2. centrifuged out, light on top, heavy on the bottom because its heavy
3. heavy nitrogen bacteria replicated in light nitrogen broth
4. conservative: DNA with ONLY heavy original strand would settle at the bottom and ONLY light new strands would settle at top
5. semi-conservation: DNA with combination of the 2 would settle in the middle