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.

Re:Horrible summary of article

[ColdWetDog]

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!"

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

Re:First confirmation? Really?

[cnettel]

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.

Polymerase chain reaction

[AlphaWolf_HK]

Any chance they could get visual confirmation of DNA replication? That would be neat to watch.

Re:Polymerase chain reaction

[Biotech_is_Godzilla]

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 cells during replication, then stop, and swap the first one out with a different artificial DNA base analogue to see the new DNA being made after the point that you change analogues. They then use fluorescently labelled antibodies to detect both types of bases, using (for e.g.) a red-labelled one for the first period of replication, and a green labelled one for the second period.

This is a good explanation. It can be used for some awesome experiments - here's an example from the same lab (Fig. 3).

Human DNA?

[jovius]

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.

Re:Human DNA?

[jo_ham]

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...

[fahrbot-bot]

abstract includes the picture that's worth a thousand words

But only four letters: A, C, T and G.

Re:First confirmation? Really?

[Brian Feldman]

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
http://en.wikipedia.org/wiki/Rod_of_Asclepius
http://ghr.nlm.nih.gov/handbook/illustrations/dnastructure.jpg