Meselson and Stahl

Question 1

What did Meselson and Stahl base their research off of?

Answer 1

Watson and Cricks discovery of the DNA structure

Question 2

What did Watson and Crick hypothesise about the way in which DNA replicated?

Answer 2

Watson and Crick hypothesised that DNA replicated either conservatively or semi conservatively

Question 3

Explain what was meant when Watson and Crick said DNA replicated “semi conservatively”

Answer 3

Semi conservative DNA replication meant that each DNA molecule replicated would contain one of the original DNA strands and one newly synthesised DNA strand

Question 4

Explain what was meant when Watson and Crick said DNA replicated “conservatively”

Answer 4

Conservative DNA replication meant that the original DNA would remain intact following DNA replication and the two newly synthesised strands of DNA would join together

Question 5

What did Meselson and Stahl conduct their experiment to prove?

Answer 5

Meselson and Stahl conducted their experiment to prove DNA replication was semi conservative

Question 6

What three facts did Meselson and Stahl base their experiment on?

Answer 6

1. DNA bases are nitrogenous (contain nitrogen)
2. Nitrogen has two isotopes 14N (lighter) and 15N (heavier)]
3. Bacteria takes in the nitrogen isotopes to make new DNA nucleotides

Question 7

If bacteria takes in the nitrogen isotopes to make new DNA molecules; what does this mean will occur?

Answer 7

This means bacteria grown in a medium containing 14N will have DNA which only contains this isotope and be lighter
Bacteria grown in the medium containing 15N will have DNA only containing the isotope 15N and be heavier

Question 8

Based on fact number three, what will have when DNA samples are spun in a centrifuge?

Answer 8

Based on fact number three, DNA samples can be spun in a centrifuge to confirm density. 15N DNA will settle lower down as it is more dense, whereas DNA with 14N will settle higher up as it is less dense