1.5 DNA replication

Question 1

name the 2 hypotheses:

Answer 1

• semi-conservative replication
• conservative replication

Question 2

what does the semi-conservative hypothesis propose

Answer 2

• 2 nucleotide chains separate like a zip,
  ∴ acting as templates for formation of further chains.
• no daughter will me made of exactly the same bases as original molecule

Question 3

what does conservative hypothesis propose

Answer 3

• a new DNA molecule will form alongside the original molecule
• in each generation, one of the DNA molecules will be exactly the same as the original molecule

Question 4

which bacteria was used for the Meselson and Stahl experiment + what isotope does it naturally contain

Answer 4

E.coli
- 14N (light)

Question 5

how was the E.coli cultured

Answer 5

• E.coli grown in a medium containing 15N (heavy), until all N-atoms are replaced by heavy isotope
• swap bacteria to new medium with normal isotope
• remove sample ∴ estimate relative amounts of 2 N-isotopes

Question 6

how are proportions of isotopes estimated?

Answer 6

• 15N are heavier than 14N, ∴ centrifuge.
• density gradient appears

Question 7

explain the process of DNA replication

Answer 7

• DNA Helicase unzips DNA,
  breaking hydrogen bonds between complementary base pairs.
• an RNA primer sequence is added. DNA Polymerase adds nucleotides with complementary bases to DNA