November 30, 2012 | 5
This blog often covers small things: insects, spiders, slime molds and so on. In the scheme of biology, though, the usual fare here is pretty big.
In contrast, here is something truly small- the first high-contrast microscope image of an isolated
molecule bundle of DNA:
Researchers at the Istituto Italiano di Tecnologia strung a molecule between two nano-towers and subjected it to transmission electron microscopy at extreme magnification. Until last week the double helix model had been an indirect inference, albeit an extremely robust one, from techniques like crystallography. The new paper, in Nano Letters, is just the thing for those who like to see evidence with their own eyes.
update: Stephen Curry provides a clarification and correction:
What is actually new in the paper is that the authors have been able to take a high-contrast image of a DNA fibre (made up of a bundle of DNA double-helices) using electron microscopy. They did this by drying out a drop of DNA dissolved in water over a layer of silicon that had been micro-fabricated to have an array of tiny pillars across its surface. As the water evaporated, strands of DNA were left stretched between the pillars. Because they are suspended above the silicon base, it was possible to get a good image of the DNA fibres (you get poorer contrast if the DNA is lying on a solid surface)…
And what do they see? There is certainly some fine structure in the image. There are repetitive features of the size expected for the helical structure in DNA. But it was clear to the Italian researchers and should have been clear to anyone looking at the picture in their online abstract, that the image is not of a single molecule of DNA but a bundle of them.
source: Gentile, F. et al. 2012. Direct Imaging of DNA Fibers: The Visage of Double Helix. Nano Lett. DOI:10.1021/nl3039162