

Rosie Redfield: No convincing evidence that As has been incorporated into DNA - bbgm
http://rrresearch.blogspot.com/2010/12/arsenic-associated-bacteria-nasas.html

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bhickey
The comments are great too. In particular I like what chemDroid had to say:

    
    
        Hi. I have posted on many places, they should not be
        doing standard DNA preps and the experiment we need 
        to see is to see a caesium chloride density gradient
        ultracentrifugation (not a gel)... If indeed the DNA 
        has arsenic, it should be getting denser and we would 
        see that as a band shift. Ethidium bromide's mode of
        action would not be affected by arsenic substition. 
    

Gels are used to measure the length of a DNA fragment. Here's how they work:
Ethidium bromide (EtBr) is an intercalating agent -- think of the DNA as a
ladder, it slides between the rungs and gets stuck there. EtBr is also
luminescent under UV. Agarose (purified seaweed extract) is used to make a gel
doped with EtBr. A DNA sample is placed in a well on one end of the gel and an
electric current is applied to the gel. The sample gets dragged through the
gel, the longer it is, the more slowly it progresses.

As chemDroid wrote, there is no reason to believe that arsenic would have any
impact on this process.

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pierrefar
You can extend the density gradient experiemnt and get the DNA out in super
pure form and then run mass spec on it to show that arsenic has indeed been
incorporated.

With a claim this important, we cannot do enough to try to disprove it. Only
after we try everything we know and get consistently convincing evidence that
arsenic is indeed incorporated into the DNA can we start believing it.

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jacquesm
I'm quite surprised at the amount of work done at NASA to push this paper as
something extraordinary without so much as a critical eye. The claim made in
the paper is extraordinary and that alone should be reason for caution, not
for bringing out the big drums.

The bigger problem is that if it turns out the result is bogus this will be a
net negative, both for NASA and for the scientific community, the public at
large will not see this as proof that 'the system works' but as proof that
they were being duped.

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Estragon
They did the same thing with the "life from Mars" thing a few years ago. It's
a way of attracting attention in order to raise money.

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jacquesm
Judging by how that worked out for them they ought to have known better. You
can only cry wolf so many times before you are labeled the village idiot, too
bad for you if the wolf eventually shows up and nobody believes you due to
'past performance'.

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waterlesscloud
I'm a big NASA supporter, but this whole episode has made me think they
deserve a little less funding.

From the way they handled the whole thing from the start with the "aliens, but
living here" spin to finding out the results aren't all that solid, it seems
they need to clean some house.

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nkassis
I don't know, it won't make a change to the way the place is administered to
reduce the budget, it's mostly going to affect the amount of money scientist
can use to advance their research. Making the quality slowly decline more.

Restructuring NASA is a hard problem maybe even impossible. But I do think
it's still producing good enough stuff that removing it would be a mistake.
I'm a believer in public research. It has produce some incredible benefits to
society in the 20th century and hopefully will continue in the 21st.

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pierrefar
You gotta love the peer review process working in public. Now (thanks to the
internet) readers correct mistakes so that by the time the paper reaches the
journals, it's already been vetted quite a bit. Before that, the public pre-
publication vetting process would have been a lot slower (e.g. to be done in
conferences) if done at all.

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waterlesscloud
It would be nice if it happened before the press conference too.

~~~
pierrefar
And miss all the publicity? Imagine a story of line of "hey we thought it was
doing this, but turns out not, so oh well". Not as enticing as "arsenic based
life form" is it?

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MrScience
Rosie Redfield is another eurasian government hack scientist operating through
colonial Canada. She claims to play the atheist card, but is a known eurasian
cheerleader, all those gods be told. Her work is pseudoscience and can never
be trusted or taken seriously. Her principle position in America is to take
American biology for the holey sleigh ride through eurasian political
hierarchy. Fortunately, she has no substantial chance of succeeding.

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kayhi
Extract the DNA. Do X-ray scattering and crystallographic studies, which would
clear this issue up nicely.

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bhickey
What would you expect to see in crystallography? A different pitch and radius
on the helix?

If that is the case, then assuming there is arsenic in the DNA: how did they
manage to PCR it? I would expect it to wreck havoc with the polymerase.

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shadowpwner
Why would arsenic wreak havoc on the polymerase?

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kayhi
My apologies if my comment implies that As creates an issue with the
polymerase. I would guess that it doesn't since amplifying the sequence was
successful.

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bhickey
My fault -- I implied it.

    
    
        I would guess that it doesn't since amplifying the sequence was successful.
    

Or the sequence doesn't contain (enough) arsenate.

