Electron Density: Cloud vs. Isomesh "Map"
Bob Hanson and Eric Martz, April 2010
Here is a piece of an electron density cloud. The cloud is calculated from a
protein crystallographic X-ray diffraction
experiment. Each point shows the electron density at a position in space. Darker points represent higher densities.
It is clear that the cloud has structure, but it is difficult to see the structure. By hiding lower densities, we can begin to see the structure.
To zoom, position your mouse at the right edge of Jmol, then drag up and down.
is a line connecting points of equal value. An
is a mesh made of isolines, e.g. connecting points with a value of 1.0 sigma of electron density.
The above example shows
, a 7-amino acid peptide with an electron density map
of 1.0 Ångstrom. Crystals of larger proteins typically have poorer resolutions. The median resolution of entries in the
Protein Data Bank
is 2.0 Ångstroms. Maps at these resolutions leave greater uncertainty in the atomic positions. On a separate page is shown an
electron density map at 2.0 Å
Bob Hanson's Demo