Cryo-electron microscopy 2235991 216110643 2008-05-31T03:12:01Z DumZiBoT 6085301 robot Adding: [[es:Criomicroscopía electrónica]] {{Nofootnotes|date=March 2008}} [[Image:cryoem groel.png|thumb|Filtered CryoEM image of [[GroEL]] suspended in [[vitreous ice]].]] '''Electron cryomicroscopy''' ('''cryo-EM''' or sometimes '''cryo-electron microscopy''') is a form of [[electron microscopy]] (EM) where the sample is studied at [[cryogenic]] temperatures (generally [[liquid nitrogen]] temperatures). CryoEM is developing popularity in [[structural biology]]. A version of electron cryomicroscopy is [[cryo-electron tomography]] (CET) where a 3D reconstruction of a sample is created from tilted 2D images, again at cryogenic temperatures (either liquid nitrogen or helium). ==Biological specimens== ===Thin film=== The biological material is spread on an electron microscopy grid and is preserved in a [[Amorphous ice|frozen-hydrated state]] by rapid freezing, usually in liquid [[ethane]] near [[liquid nitrogen]] temperature. By maintaining specimens at liquid nitrogen temperature or colder, they can be introduced into the high-[[vacuum]] of the [[electron microscope]] column. Most biological specimens are extremely [[radiation]] sensitive, so they must be imaged with low-dose techniques (usefully, the low temperature of cryo-electron microscopy provides an additional protective factor against [[radiation]] damage). Consequently, the images are extremely [[Signal noise|noisy]]. For some biological systems it is possible to average images to increase the signal-to-noise ratio and retrieve high-resolution information about the specimen. This approach requires that the things being averaged are identical (e.g. [[ribosome]] particles). Analysis of ordered arrays of protein, such as 2-D [[crystals]] of [[transmembrane proteins]] or [[helical]] arrays of proteins, also allows a kind of averaging which can provide high-resolution information about the specimen. This technique is called [[electron crystallography]]. ===Vitreous sections=== The thin film method is limited to thin specimens (typically < 500 nm) because the electrons cannot cross thicker samples without multiple scattering events. Thicker specimens can be vitrified by plunge freezing in ethane (up to tens of μm in thickness) or more commonly by [[high pressure freezing]] (up to hundreds of μm). They can then be cut in thin sections (40 to 200 nm thick) with a diamond knife in a cryoultramicrotome at temperatures lower than -135 °C (devitrification temperature). The sections are collected on an electron microscope grid and are imaged in the same manner as specimen vitrified in thin film. This technique is called cryo-electron microscopy of vitreous sections (CEMOVIS) or cryo-electron microscopy of frozen-hydrated sections. == See also == * [[Software tools for molecular microscopy]] * [[Resolution (electron density)]] ==References== <div class="references-small"> *{{cite book | last = Frank | first = Joachim | authorlink = Joachim Frank | title = Three-Dimnsional Electron Microscopy of Macromolecular Assemblies | publisher = [[Oxford University Press]] | location = New York | date = 2006 | pages = | isbn = 0-19-518218-9 }} </div> ==External links== *[http://www.technologyreview.com/Biotech/20436/ The Fine Structure of a Frozen Virus] - Sophisticated single-particle electron cryomicroscopy reveals unprecedented details in a virus's protein coat, ''Technology Review'', March 19, 2008 [[Category:Microscopes]] [[Category:cell biology]] [[Category:Protein structure]] [[es:Criomicroscopía electrónica]]