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!?
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.
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.
Re:Polymerase chain reaction (Score:3, Informative)
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 [cam.ac.uk]. It can be used for some awesome experiments - here's an example from the same lab (Fig. 3) [sciencedirect.com].