2. Evidence Of DNA Replication Flashcards
Who validated the theory of semi conservative replication?
Meselson and stahl
What were people initially unsure about ?
If dna replication was semi conservative or conservative.
What would happen if the method was conservative ?
The original strands would stay together and new dna molecules would contain 2 new strands.
What did the experiment use ? 2 things.
2 isotopes.
Heavy nitrogen 15N
Light nitrogen 14N
What are isotopes?
Different forms of the same element
- How many samples of bacteria where grown and for how long ?
2 samples of bacteria.
One in nutrient broth of light nitrogen and one in broth of heavy nitrogen.
Grown for generation.
- What happened as the bacteria in broth reproduced?
They took up nitrogen from the broth to make new nucleotides for new dna.
So nitrogen gradually became part bacteria’s Dna
- A sample of dna took from both batches of bacteria , what was done to them ?
Spun in a centrifuge.
- What did the results show when bacteria’s were put in centrifuge?
The dna from heavy nitrogen bacteria settled lower down centrifuge tube than the dna from light nitrogen bacteria - because it’s heavier.
- The bacteria grown in heavy nitrogen was taken out and where was it put?
In broth containing only light nitrogen.
Left here for 1 round of dna replication.
Then dna sample was taken out and spun in centrifuge.
- So after adding heavy nitrogen with light nitrogen, what would happen if it was conservative?
The original heavy dna would still be together at bottom and new light dna would settle at the top.
- What would happen is replication was semi conservative?
New bacterial dna molecules would contain 1 strand of old dna containing heavy nitrogen and one new strand containing light nitrogen.
So dna would settle between where light nitrogen settled and heavy nitrogen settled.
- So what did replication of our dna show ?
Dna settled in the middle showing dna contained mixture of heavy and light nitrogen. - semi conservative
