Griffith and his role with DNA discovery

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evointrigued
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Griffith and his role with DNA discovery

Post by evointrigued » Fri Nov 30, 2007 4:16 pm

I'm reading about his experiments with S-strain and R-strain Streptococcus pneumoniae. It says there was "heat-killed" S-stains that were normally pathogenic but weren't after they were heat-killed. Does this literally mean high temperature was applied? If so, would it be accurate to say DNA can withstand much more heat than proteins?

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Post by humbledaisy » Fri Nov 30, 2007 6:23 pm

Someone can please correct me if i am wrong! But I would answer yes to both your questions- I am currently studying DNA analysis, and to extract DNA from a sample we heat it to quite high temperatures to remove whatever RNA and proteins may also be in the sample. Hope this helps!

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Navin
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Post by Navin » Fri Nov 30, 2007 7:22 pm

Yes - I think DNA is heatstable when compared to proteins and RNA.

I think its got to do with its unique structure that makes it more stable than RNA (This is why our genome is made of the more stable DNA, not RNA), and we know that most proteins (particularly enzymes) denature at high temperatures (except a few like the Taq polymerase and such...)

So, I'm guessing that the heat denatured the pathogenic strains' bacterial proteins, and probably broke down the cell wall, thus releasing the DNA into the surroundings. The DNA may have fragmented though - (i'm not sure bout this bit). But i know the next step is transformation followed by homologous recombination - converting the non-pathogenic strain to the pathogenic strain.
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canalon
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Post by canalon » Sat Dec 01, 2007 4:57 am

DNA is really stable. Remember that in PCR you boil it (or almost) and it renatures almost immediatly. In fact by boiling you also degrade most of the surrounnding DNAse that might have been released when the bacteria died. Basically at those temp you lose the double helix, but it forms back as soon as the temp decrease. And in the absence of mechanical forces, the DNA should not even break
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