2. DNA replication

Question 1

what is DNA replication called?

Answer 1

semi-conservative replication

Question 2

outline the process of semi-conservative DNA

Answer 2

1. DNA helicase unwinds the DNA strands, as it hydrolyses the hydrogen bonds between the two strands
2. free nucleotides join to the exposed bases via complimentary base pairing, AT, CG
3. the complimentary nucleotides and bases are joined via condensation reactions catalysed by DNA polymerase, forming hydrogen bonds between the bases of the two strands
4. each new DNA molecule contains one strand from the original DNA molecule and one new strand

Question 3

how does DNA polymerase work

Answer 3

• moves along the strand from the 3 prime to 5 prime direction
• this is due to the fact that DNA polymerase is only complimentary to the 3 prime end
• meaning that DNA polymerase has to constantly attach to and detach in order to work along the strand

Question 4

who proved that DNA replication was semi conservative

Answer 4

Meselson and Stahl

Question 5

outline the Meselson and Stahl experiment

Answer 5

• samples of heavy and light DNA containing varying nitrogen nad isotopes were grown
• the heavy nitrogen were put into a broth containing the light nitrogen
• they found after a generation, the DNA contained a band of each band, with the DNA settling halfway between the original
• this is what they found which supports the theory of semi-conservative DNA replication