First Direct Image of DNA Double Helix

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.

Comments

Horrible summary of article

[Dahamma]

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

[ColdWetDog]

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

[Dahamma]

It appears that this was translated poorly from the original Italian.

I don't think so. If the full article was in Nano Letters, 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.

for those wondering what the picture shows

[Anonymous Coward]

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.

Re:First confirmation? Really?

[Dahamma]

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?

[AHuxley]

Some fun art from c1910 by a Swedish artist named Hilma Af Klint
http://www.wikipaintings.org/en/hilma-af-klint/what-a-human-being-is-1910