Visualising proteins

Atomic level structures of proteins are visualised by x-ray crystallography, NMR (nuclear magnetic resonance), EM (electron microscopy) or SPA (single particle analysis).

• X- ray crystallography requires the growth of protein crystals, which is relavitely simple. It requires diffraction to be measured from the protein crystal. Information is produced in a series of black dots, which are reflections, to form the basis of structure solution. Eventually this comes together to form a 3D image. 
• NMR studies proteins in solution but is limited to only small medium proteins.
• EM/SPA are more suited to large protein complexes and viruses. EM uses magnetic coils to focus a beam of electrons on the specimen. The sample in the EM must be kept in a vacuum. This has more penetrating power than light microscopy. SPA involves taking many images of a sample frozen in water in random orientations. These 2D images can then be combined to provide a 3D view of the protein.

The equiptment used to carry out such techniques is very expensive.