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 is one of the most basic techniques used in determining the strutures of biological molecules like proteins. This is done through measuring the many short proton-proton distances and angles and restraining the protein structure with these computationally. 
  
• 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.
• Intrinsic label microscopy uses Green Flourescent Proteins found in Jellyfish. These emit green light and when recombinant proteins are made with the gene for GFP, they will emit a natural green light. This allows us to visualise the size and position of the protein in the cell. This technique can work in all cell types. However, this technique can have inaccurate results due to GFP's tendancy to dimerise. 

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