X-Ray Analysis of Prokaryotic and Eukaryotic Ribosomes - Biophysical Approaches to Translational Control of Gene Expression - page 1

Chapter 1
X-Ray Analysis of Prokaryotic
and Eukaryotic Ribosomes

Lasse B. Jenner , Adam Ben-Shem , Natalia Demeshkina ,
Marat Yusupov, and Gulnara Yusupova

1.1 X-Ray Crystallography and the Ribosome

1.1.1 X-Ray Methodology

X-ray crystallography is an experimental technique that takes advantage of the fact
that X-rays are scattered by electrons. Using electromagnetic radiation to visualize
objects by scattering requires the wavelength of the radiation to be comparable to the
smallest features to be resolved. Since the atomic bond lengths most commonly
found in biological materials are in the 1-2 Angstrom (Å) range, the X-rays pro-
duced by in-house rotating anodes and large-scale facilities such as synchrotrons are
well suited for this purpose. While scattering from one molecule is too weak to be
measured, diffraction from a crystal containing millions of molecules all oriented in
a regularly repeated manner is detectable. The diffraction data acquired by X-ray
scattering off the periodic assembly of molecules in the crystal can be used to recon-
struct the electron density. Electron distributions observed this way provides the
locations of the atomic nuclei. An atomic model is iteratively constructed and refined
into the observed electron density leading to a rather accurate molecular structure.