MBB 222 Chapter Notes - Chapter 5.3: X-Ray Crystallography, Protein Crystallization, Phase Problem
6 Nov 2018
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Document Summary
X-ray crystallography is based on the diffraction of x-rays by protein crystals. The x-rays diffracted by the crystal are captured using electronic x-ray detectors. Multiple diffraction images are collected from successive rotations of the crystal, measuring the intensity of x-rays scattering in all directions. Much as a lens can recombine scattered light to form an image, these measurements of the scattered x-rays can be combined using computational methods to form an image. In the case of crystallography, the image is a three-dimensional map of the electron-dense regions of the crystal (called an electron density map). A model of the protein is then built to match the regions of electron density, which is rendered by a computer graphics program. The two most difficult steps in x-ray crystallography are (1) growing diffraction-quality crystals and (2) determining the phases of the diffracted x-rays. Crystals are needed in order to provide sufficient mass for scattering x-rays, as an individual protein is too small.
