Cryo-electron microscopy of biological samples

A brief summary of current cryo-electron microscopy methods for processing and imaging biological tissues is provided. The main emphasis is given to two preparation procedures: frozen-hydrated samples because of the remarkable success of cryo-electron crystallography in obtaining near atomic resolution of integral membrane proteins, and high-pressure freezing because of the wide applicability for vitrification of large samples of normal and diseased tissues for ultrastructural and immunolabeling analysis. Methods for examining certain samples with a TEM cryo-stage are summarized. This includes an introduction to the relatively new area of cryo-electron tomography, which offers the possibility to observe the three-dimensional structure of subcellular components using only their natural variations in composition to generate contrast.