Cryoelectron tomography

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Three-dimensional representation of an Ostreococcus Tauri cell using a cryoelectron microscope

The cryo-electron tomography (v. Greek. Κρύος frost , ice , τομή "cut" and γράφειν "write") is an imaging method for three-dimensional representation of finest structures. It is used in particular in researching cell structures in biology and medicine . The cell structure can be viewed directly without changing the structure through chemical pretreatment, staining or thin sections. To accommodate the tomograms one is Kryoelektronenmikroskop used which cost several million euros.

functionality

First, the object is cooled down to four Kelvin using liquid nitrogen or helium . The lightning-fast freezing preserves the spatial structure of all cell components. At the same time, it is avoided that the cells burst during the subsequent examination in the vacuum of an electron microscope . A vacuum is required because electron beams are deflected by gas molecules or dust particles.

After the specimen has been fixed in the electron microscope, a high-resolution camera is used to record two-dimensional images of the object from many different tilt angles of the specimen. Usually, CMOS cameras are used because they have a much higher electron sensitivity than traditional CCD sensors . Phase plates or an energy filter can also be used to improve contrast .

As many individual images as possible are required for the subsequent representation of the cell structures in space. However, this also increases the duration of the irradiation. In order to prevent the ice from melting or crystallizing, the lowest possible illuminance levels are used. Computer-aided control of these parameters is intended to prevent the sample from spoiling before the tests are completed.

With the help of special software, the serial images obtained are later converted into a three-dimensional image.

history

Cryoelectron tomography was developed from 1987 onwards by a research group led by one of the directors of the Max Planck Institute for Biochemistry in Martinsried near Munich, Wolfgang Baumeister . It was initially unclear whether cell components with a size of a few nanometers can be represented three-dimensionally. During intensive preparatory work with proteins whose structure was known, both the recording technology and the image analysis were optimized and automated.

From 2002 onwards, new knowledge about the communication and interaction of different molecular complexes and cell organelles inside a cell could be gained with this technology . Wolfgang Baumeister was awarded the Ernst Schering Prize in 2006 for the development of cryoelectron tomography . In 2007, with the help of cryoelectron tomography, it was possible for the first time to examine a complete unicellular living being with a cell nucleus and cell membrane.

application

With cryoelectron tomography, intact cell structures can be examined at the molecular level. Due to the higher resolution, it offers far deeper insights into the cell structure than conventional light microscopy. The aim of Baumeister's research is "to describe the complex model of the entire cell, not just the functions of individual molecules and organelles, as was previously possible, but of the entire cell structure".

The process is currently leading to a multitude of new discoveries in cell, neuro and infection biology, such as: B. the representation of unknown structures in the cell skeleton of malaria pathogens .

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