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AQA AS Biology spec help needed (DNA)

Hi,

In the spec it says 'evaluate the work of scientists invalidating the Watson–Crick model of DNA replication'.

I'm not really sure what this means? If anyone has notes etc. on it or can tell me what i need to find out, that would be great thanks :smile:

I hope everyone's revision is going well!
Original post by Laurenloops
Hi,

In the spec it says 'evaluate the work of scientists invalidating the Watson–Crick model of DNA replication'.

I'm not really sure what this means? If anyone has notes etc. on it or can tell me what i need to find out, that would be great thanks :smile:

I hope everyone's revision is going well!


I think they're talking about how you should appreciate that other scientists like Rosalind Franklin studied DNA using X-ray diffraction to discover that DNA is a double helix because Watson and Crick initially thought it was a triple helix. I remember reading this somewhere.
It refers to this,https://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120076/bio22.swf::Meselson%20and%20Stahl%20Experiment
The Meselson and Stahl experiment (you dont have to know the name dont worry), was the experiment that proved the semi conservative model of DNA replication
Original post by boredom07
I think they're talking about how you should appreciate that other scientists like Rosalind Franklin studied DNA using X-ray diffraction to discover that DNA is a double helix because Watson and Crick initially thought it was a triple helix. I remember reading this somewhere.


That's DNA structure not about DNA Replication.

Hazan is correct, it is referring to the work of Meelson and Stahl's experiment with a heavy isotope of nitrogen and a light isotope of nitrogen to prove that DNA replicates semi-conservatively.
Original post by CrazyFool229
That's DNA structure not about DNA Replication.

Hazan is correct, it is referring to the work of Meelson and Stahl's experiment with a heavy isotope of nitrogen and a light isotope of nitrogen to prove that DNA replicates semi-conservatively.


Oops, misread it :tongue:
It refers to the evidence for DNA replication being semi-conservative (which was proposed by the Watson-Crick model)- this was done by Meselson and Stahl.
They used 'Heavy' Nitrogen (15N) as a medium to grow 1 generation of bacteria and then transferred the second generation (after 20 minutes) to a 'Light' (14N) medium and separated the two isotopes using centrifugation...
This may help: https://www.youtube.com/watch?v=Kaix15vjmxM
:smile:

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