Practical Protein Chemistry - A. Darbre 1989

X-ray Crystallography and Electron Microscopy
X-ray Diffraction
Computer-Aided Molecular Modeling

Computer-assisted molecular modeling undoubtedly offers A number of advantages over the physical method described above, although it is not without drawbacks. Rapidly advancing computer graphics can generate images of the Structure/83.html">Structural elements of molecules (such as Amino Acids) and superimpose them onto electron density map contours. This is achieved by displaying orthogonal images or stereo pairs of structural elements on the screen simultaneously with a three-dimensional electron density map (Fig. 20.11). The advantages of such systems include The ability to automatically refine the positions of amino acid residues, account for Van der Waals interactions, and introduce additional notations, such as dashed lines to indicate THE POSITION OF Hydrogen Bonds. It must be admitted that using computer graphics tools is preferable despite the high cost of graphic devices and their software, as well as current limitations on calculation speed and the size of displayed structures. These limitations mean that only relatively small segments of a polypeptide chain can be rendered on the screen.

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FIG. 20.11. The B5–B8 region of the Insulin molecule structure rendered using computer graphics. The electron density map and structural model are displayed on the screen simultaneously.