Electron crystallography is a method to determine the arrangement of atoms in solids using an electron microscope. It can complement X-ray crystallography on proteins (such as membrane proteins), that cannot easily form the large 3-dimensional crystals required for that process. Structures are usually determined from either 2-dimensional crystals (sheets or helices), polyhedrons such as viral capsids, or dispersed individual proteins. Electrons can be used in these situations, whereas X-rays cannot, because electrons interact more strongly with atoms than X-rays do. Thus, X-rays will travel through a thin 2-dimensional crystal without diffracting significantly, whereas electrons can be used to form an image. Conversely, the strong interaction between electrons and proteins makes thick (e.g. 3-dimensional) crystals impervious to electrons, which only penetrate short distances. This article does not cite its references or sources. ... X-ray crystallography is a technique in crystallography in which the pattern produced by the diffraction of X-rays through the closely spaced lattice of atoms in a crystal is recorded and then analyzed to reveal the nature of that lattice. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle. ... Quartz crystal In chemistry and mineralogy, a crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered, repeating pattern extending in all three spatial dimensions. ... A helix (pl: helices), from the Greek word έλικας/έλιξ, is a twisted shape like a spring, screw or a spiral staircase. ... A polyhedron is a geometric shape which in mathematics is defined by three related meanings. ... The outer shell of a virus is called the capsid. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...

One of the main difficulties in X-ray crystallography is determining phases in the diffraction pattern. Because no X-ray lens exists, X-rays cannot be used to form an image of the crystal being diffracted, and hence phase information is lost. Fortunately, electron microscopes contain electron lenses, and phase information tends to be much more reliable in electron crystallography. To meet Wikipedias quality standards, this article or section may require cleanup. ... Diffraction is the apparent bending and spreading of waves when they meet an obstruction. ... A lens. ...

A common problem to X-ray crystallography and electron crystallography is radiation damage, by which proteins are damaged as they are being imaged, limiting the resolution that can be obtained. This is especially troublesome in the setting of electron crystallography, where that radiation damage is focused on far fewer atoms. One technique used to limit radiation damage is electron cryomicroscopy, in which the samples undergo cryofixation and imaging takes place at liquid nitrogen or even liquid helium temperatures. Because of this problem, X-ray crystallography has been much more successful in determining the structure of proteins that are especially vulnerable to radiation damage. Electron cryomicroscopy is a form of electron microscopy (EM) where the sample is studied at cryo temperatures (generally liquid nitrogen temperatures). ... General Name, Symbol, Number Nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15 (VA), 2 , p Density 1. ... Helium exists in liquid form only at very low temperatures. ...

The first electron crystallographic protein structure to achieve atomic resolution was bacteriorhodopsin, determined by Richard Henderson and coworkers at the Medical Research Council Laboratory of Molecular Biology in 1990. Since then, several other high-resolution structures have been determined by electron crystallography, including the light-harvesting complex, the nicotinic acetylcholine receptor, and the bacterial flagellum. Bold textLink titleLink title Bacteriorhodopsin is the photosynthetic pigment used by archaea, most notably halobacteria. ... Richard Henderson (b. ... Current MRC logo The Medical Research Council (MRC) is a UK organisation dedicated to promot[ing] the balanced development of medical and related biological research in the UK. Organisation The MRC is one of seven Research Councils and is answerable to, although politically independent from, the Office of Science and... MRC Laboratory of Molecular Biology, Cambridge EXTERNAL LINKS www. ... This article is about the year. ... A light-harvesting complex is one or more polypeptide chains containing photosynthetic pigments, which surrounds a photosynthetic reaction centre and focuses light inward toward its core. ... Nicotinic acetylcholine receptors, or nAChRs, are ionotropic receptors that form ion channels in cells plasma membranes. ... A flagellum (plural, flagella) is a whip-like organelle that many unicellular organisms, and some multicellular ones, use to move about. ...

External links

• Interview with Aaron Klug Nobel Laureate for work on crystallograph electron microscopy Freeview video by the Vega Science Trust.