In this technology, which is dried the sample down in a puddle of a Schwermetallsalzes (usual Uranylazetat) this, the structure supports and prepares its surface properties. Strong image contrast results from the scattering difference between the heavy metal, the structure and the protein surrounding, which are seen as bright article in a darker background. The philosophy of cryo EM is very simple and in table 2.2 is illustrated. A drop of the copy of the interest is applied at a continuous or holey or lacey carbon film to a EM-raster field, reduces the strength, by staining with filter paper and dipped then, into the liquid ethane, which is maintained near at its freezing point by liquid ethane. Undercooling takes place at something 104,106 C/s with the result of the glazing of a thin copy in the woman to the woman time sequence. Surplus ethane is stained away and the raster field is then brought into a cooling down owner of the copy for examination and photography near at temperature of the liquid nitrogen. Refinements to freezing equipment nowpermit the control of parameters such as humidity and temperature before freezing, which automated, reproducible to cause staining and the release of cagedmolecules or of Sprühofmolecules defined changes straight before freezing. Because the sample is chemically untreated, it is acutely sensitive to damage by the ray of light of the ionizing radiation and empfindlilch (much, there we! ) and must be shown under the lowest dose conditions, those would be with an acceptable compatibly are breakdownsignaling relationship. To a first approximate value scattering of the electrons is proportional to the density of the material. Thus a protein, with a density of 1.3, is seen as the darker article in the less close aqueous background (density 0,95 for ice), therefore it means that the contrast was waived compared to Sichtbarmachung in the negative mark. Table 2.3 bacterium that appearance T4 as example. The contrast, which is reached, is low and normally increased by the Defocusing the objective objective.
Electron microscopes are able to make pictures available at the very high linear rendition. There is however a compromise between highs and low-linear rendition. A microscope is sketched too its optimal electron-optical achievement at the high linear rendition gives however electron dose (for the same optical density on the film) depends on the squared linear rendition. Therefore she is from the acute interest, to know on, how low supplies with a linear rendition a certain EM still to atomic resolution. The restriction a magnetic wandering around field is frequent. A further complication is that the received pictures do not supply a direct to representation with of the spatial density distribution of the copy. The results of contrast changed by the scattering differences between the protein and the water by the characteristics of the objective objective. Image contrast results from two components: Extent and phase. By the absorption or the electrons absent-minded by strong scattering of the incident ray of light by the sample with Blendenöffnung removes results of extent contrast from the picture by the objective. For a thin cryo copy the extent contrast is resulted on estimated 7 per cent phase contrast made of disturbance of the flexibly scattered electrons with unscattered the ray of light; the range of the absent-minded wave is untouched. It is, as if the article transparency were.
Such thin, uncolored, biological samples only the dispersion electrons by small angles are frequently described, while `the weak additional phase contrast of phase articles is introduced generally by the Defocusing the objective objective if spherical deviation the contrast from pictures further increased. A in more detail description of the picture arrangement can be found in Reimer (1997). The Sichtbarmachung of weak phase objects, by it results in the considerable complexity defocusing, if it interprets the picture as simple projection of the copy. This develops, because picture details can be present in a certain size distance in the picture with different contrast, even locks you for contrast detour. Many years of the analysis resulted in the development of the expert software, in order to repair the original density distribution of pictures. This characterized as correction of the contrast transient response of the EM (or simply CTF correction). After this correction the picture of the weak phase article can be respected as an applicable two-dimensional projection of the three-dimensional article. This makes the use possible of special mathematical beginnings to achieve a complete three-dimensional density distribution for the article.
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