X-Ray Crystallography

TLDR: X-ray crystallography is a technique for determining the detailed three-dimensional structure of molecules, including complicated biological macromolecules such as proteins and nucleic acids as mentioned in this paper, which requires highly purified material prepared in crystalline form.

Abstract: X-ray crystallography is a technique for determining the detailed three-dimensional structure of molecules, including complicated biological macromolecules such as proteins and nucleic acids. The interpretation of X-ray diffraction patterns to determine the molecular structure of crystallized matter traces its roots to the early part of the twentieth century. The experiment requires highly purified material prepared in crystalline form. Diffraction data are collected by passing a beam of collimated X-rays through a single crystal and accurately measuring the position and intensity of each diffracted ray. This intensity information must then be combined with some estimate of phases before a three-dimensional envelope of electron density can be calculated and the periodic repeating arrangement of atoms in the crystal can be deduced. This method has been used to determine with extremely high precision the three-dimensional arrangement of atoms within whole viral capsids, nucleic acid polymerases, ribosomes, membrane channels, and many other macromolecular systems of biological interest.