Perspectives and outlook for electron microscopy in biology in general

The possibilities for improving methods of electron microscopy with the aim of visualizing still finer details of biological relevance are discussed with respect to different goals: discovering and defining new structures in situ, in the cell, in relation to functions, and investigating the fine structure of already morphologically and biochemically defined structures which are available in isolated and purified form. For each of these goals the importance of the inherent limitations are considered: lack of definition due to the unknown nature of heavy metal staining, deformations caused by the physical events of specimen preparation, and radiochemical alterations induced by the electron beam. Methods of investigating and overcoming these limitations by new cryotechniques, new imaging modes and improved crystallographic techniques are outlined. Emphasis is given to relevant biological phenomena, where electron microscopy is potentially the method of choice, e.g., those related to functional proteins situated in and on biological membranes and where relatively large conformational changes are supposed to have occurred to explain the functions.