First Direct Image of DNA Double Helix 44
New submitter bingbat writes "Scientists at the University at Genoa, Italy have successfully photographed the double-helix structure of a single strand of DNA, using a tunneling electron microscope. This marks the first visual confirmation of its structure." The full paper is behind a paywall, but the linked abstract includes the picture that's worth a thousand words.
Horrible summary of article (Score:5, Informative)
Summary: "structure of a single strand of DNA"
TFA: "Here we report on the direct imaging of double stranded (ds) -DNA"
Summary: "using a tunneling electron microscope"
TFA: "with transmission electron microscopy (TEM)"
Yes, the full paper is beyond a paywall, but couldn't you have even summarized the three sentence abstract correctly!?
Re:Horrible summary of article (Score:5, Interesting)
That's a tad confusing, but so is the 'article':
Direct imaging becomes important when the knowledge at few/single molecule level is requested and where the diffraction does not allow to get structural and functional information. Here we report on the direct imaging of double stranded (ds) -DNA in the A conformation, obtained by combining a novel sample preparation method based on super hydrophobic DNA molecules self-aggregation process with transmission electron microscopy (TEM). The experimental breakthrough is the production of robust and highly ordered paired DNA nanofibers that allowed its direct TEM imaging and the double helix structure revealing.
It appears that this was translated poorly from the original Italian. A strand of DNA could be a single polymer of DNA or double stranded - where complementary sequences are bound together in the traditional 'double helix' - 'strand' being a poor choice of words in this context. It's not clear where the tunneling electron microscope idea came from.
It's also not clear that the picture represents and image of either single or double stranded DNA. It appears to be a linear polymer of a number of double stranded DNA molecules. You can see a helical structure, but it appears that that you are looking at a group of DNA molecules bound together. Unfortunately, the paucity of information in the abstract and the poor translation make it unclear what, if anything, we learn with this technique.
Re:Horrible summary of article (Score:5, Informative)
It appears that this was translated poorly from the original Italian.
I don't think so. If the full article was in Nano Letters [acs.org], they published it in English.
It's not clear where the tunneling electron microscope idea came from.
I'm guessing the poster figured "TEM" meant tunneling election microscope, when it really means transmission electron microscope, vs. "STM" (scanning tunneling microscope). Though jeez, the article actually spells it, out, so it's a pretty lame mistake.
It's also not clear that the picture represents and image of either single or double stranded DNA. It appears to be a linear polymer of a number of double stranded DNA molecules. You can see a helical structure, but it appears that that you are looking at a group of DNA molecules bound together.
Yup, from a different summary I read they claimed it was a bundle of 7 molecules (6 around a core), apparently (for what their explanation is worth) because a single one would be destroyed by the TEM.
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It appears that this was translated poorly from the original Italian.
I don't think so. If the full article was in Nano Letters [acs.org], they published it in English.
You beat me to it. I don't know HOW that abstract made it through. The ACS kept telling me that they could only maintain their current level of quality publishing if I kept giving them money, but I didn't realize they actually meant it!
Yup, from a different summary I read they claimed it was a bundle of 7 molecules (6 around a core), apparently (for what their explanation is worth) because a single one would be destroyed by the TEM.
I am by no means a TEM expert, but I did spend a semester learning to use one in grad school (in a bio class all my materials chemistry classmates taunted me for taking), and it only a m
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You beat me to it. I don't know HOW that abstract made it through. The ACS kept telling me that they could only maintain their current level of quality publishing if I kept giving them money, but I didn't realize they actually meant it!
"Subscribe to our journal or the article gets it!"
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Yes, the full paper
It is not a paper, it is just a letter.
is beyond a paywall
$35 for 48 hours of access? Really?
First confirmation? Really? (Score:1)
Didn't X-ray crystallography visually confirm the structure of DNA long ago?
Re:First confirmation? Really? (Score:5, Insightful)
No, X-ray crystallography was an indirect confirmation - sort of like the current methods for detecting extrasolar planets.
This was actually directly photographing the helix, which is novel - though according to other (much better!) summaries it's still not of a single (or even double) DNA molecule:
"This technique will allow researchers to view single molecules of DNA interacting with other molecules. For now, the method only works with cords of DNA, made up of six molecules wrapped around a seventh acting like a core. This was needed because the energy of the electron streams could break apart a single DNA molecule."
Re:First confirmation? Really? (Score:4, Interesting)
The main problem of the experiments of the Watson-Crick era was that the diffraction pattern was created by the average along the helix, so you could not really discern individual nucleotides. Considering diffraction by itself to somehow be inferior to transmission techniques is not very convincing, in my opinion. It's not even like the scientists can visually see this with their own eyes - and even if they could, the interpretation would be totally dependent on the design of the equipment, just like reconstruction of diffraction data is dependent on a number of assumptions.
What's relevant and interesting is the fact that we get close to observing individual molecules of DNA in detail, but that could be done with techniques for single-molecule diffraction as well.
Re:First confirmation? Really? (Score:5, Interesting)
http://www.wikipaintings.org/en/hilma-af-klint/what-a-human-being-is-1910 [wikipaintings.org]
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Some more on her work at http://www.guardian.co.uk/culture/2006/mar/14/2 [guardian.co.uk]
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No, you are confusing it with the Caduceus (which is itself confused with the Rod of Asclepius). The double-helix is stacked/offset, not intertwined.
http://en.wikipedia.org/wiki/Caduceus [wikipedia.org]
http://en.wikipedia.org/wiki/Rod_of_Asclepius [wikipedia.org]
http://ghr.nlm.nih.gov/handbook/illustrations/dnastructure.jpg [nih.gov]
for those wondering what the picture shows (Score:5, Informative)
the two pillars in the upper pics (SEM images) are some kind of super hydrophobic structure designed to hold the DNA molecule, the thin line connecting the tops of the columns is the DNA itself, the holes in the bottom allow the TEM electron beam to photograph the helix. the bottom right pic is the TEM image.
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Thank you, no idea why the picture could have a caption such as yours to explain this.
Because the audience is not a bunch of nerds on a tech news site, but scientists in a nanofabrication lab.
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Is it writable (Score:2)
Brings to mind the teams which were using an instrument like the SEM to deposit atoms on to a surface. Could the same be done with DNA, ie, use the needle to modify the molecule?
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I think you are confusing the TEM (electron transmission) microscope that operates with the help of an electron beam, with an AFM (atomic force microscope) which does indeed use a needle and can displace atoms on the surface of a material.
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Yes, probably.
First Impression (Score:2)
DNA is a pipe cleaner.
Polymerase chain reaction (Score:3)
Any chance they could get visual confirmation of DNA replication? That would be neat to watch.
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They already have a visual confirmation of DNA replication, obtained by transmission electron microscopy again.
Google "replication fork TEM" for some images. You have to prep DNA from cells, you can't see it happening inside cells, but it's very strong visual evidence of how replication happens.
There's also a cool visualisation method that allows you to see new DNA being laid down during replication using confocal (laser) microscopy. The way it works is: they feed an artificial version of a DNA base to cell
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Hmm...if they saw DNA earlier by seeing a PCR fork, why would this be the first time they "see" DNA? It looks apparent in those other pictures.
Is there something different about this?
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You mean replication fork. "PCR fork" is not a meaningful term. PCR is an artificial way to replicate DNA, and is very different to, and much less complicated than, in vivo (in the cell) DNA replication.
You're right, though, this is not the first time they've visualised DNA. It may be the first time they've visualised it using electron microscopy at a resolution that means you can actually see what its fine structure looks like, instead of it looking like a smooth line, but we already had a good idea what t
Kids^W Scientists these days (Score:2)
I hope everyone on this team has read The Double Helix, so they know just how much imaginative work was done back in the day to figure out what they just confirmed visually. While writing that I also had the amusing thought that I hope James Watson calls them up and tells them to get off his lawn.
Human DNA? (Score:4, Insightful)
If it was human this is the first time DNA took a photo of itself. It took a few million years and much learning and understanding to realize the present capabilities, but finally we are there.
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If it was human this is the first time DNA took a photo of itself. It took a few million years and much learning and understanding to realize the present capabilities, but finally we are there.
Just consider, if you leave hydrogen around for long enough it eventually becomes something that can work out what hydrogen is.
A thousand words... (Score:3)
abstract includes the picture that's worth a thousand words
But only four letters: A, C, T and G.