Resolution: Difference between revisions

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==What Limits Resolution?==

In crystals of macromolecules, it is the degree of order in the crystal that limits the resolution of X-ray crystallography. Resolution is theoretically limited by the wave length of X-rays (on the order of 1 Å), but in practice, the quality of the available crystals determines resolution. More than half of the crystals obtained from various purified proteins are not of "atomic resolution", that is, the disorder it too great to permit determination of molecular structure. Perhaps the greatest challenge facing crystallographers is to obtain a well-ordered crystal that diffracts to "atomic resolution".

In crystals of macromolecules, it is the degree of order in the crystal ("quality of the crystal") that limits the resolution of X-ray crystallography. Resolution is theoretically limited by the wave length of X-rays (on the order of 1 Å), but in practice, the quality of the available crystals determines resolution. More than half of the crystals obtained from various purified proteins are not of "atomic resolution", that is, the disorder it too great to permit determination of molecular structure. Perhaps the greatest challenge facing crystallographers is to obtain a well-ordered crystal that diffracts to "atomic resolution".

The resolution of a diffraction pattern depends on how ordered the crystal is. If it is highly ordered (atoms are in defined positions throughout the crystal and over time), the crystal will diffract to high resolution. The more disorder there is (atoms moving over time, or the content of one unit cell differing from the next), the lower the resolution of the diffraction image. The intensity of diffraction spots drops with increasing disorder. In order to be able to measure weak reflection spots, it is sometimes possible to increase the intensity of the X-rays used in the experiment, increase the exposure time or sensitivity of the detector, or increase the size of the crystals.

==Electron Density Map vs. Resolution==

Resolution: Difference between revisions

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 ==What Limits Resolution?==
-In crystals of macromolecules, it is the degree of order in the crystal that limits the resolution of X-ray crystallography. Resolution is theoretically limited by the wave length of X-rays (on the order of 1 Å), but in practice, the quality of the available crystals determines resolution. More than half of the crystals obtained from various purified proteins are not of "atomic resolution", that is, the disorder it too great to permit determination of molecular structure. Perhaps the greatest challenge facing crystallographers is to obtain a well-ordered crystal that diffracts to "atomic resolution".
+In crystals of macromolecules, it is the degree of order in the crystal ("quality of the crystal") that limits the resolution of X-ray crystallography. Resolution is theoretically limited by the wave length of X-rays (on the order of 1 Å), but in practice, the quality of the available crystals determines resolution. More than half of the crystals obtained from various purified proteins are not of "atomic resolution", that is, the disorder it too great to permit determination of molecular structure. Perhaps the greatest challenge facing crystallographers is to obtain a well-ordered crystal that diffracts to "atomic resolution".
+The resolution of a diffraction pattern depends on how ordered the crystal is. If it is highly ordered (atoms are in defined positions throughout the crystal and over time), the crystal will diffract to high resolution. The more disorder there is (atoms moving over time, or the content of one unit cell differing from the next), the lower the resolution of the diffraction image. The intensity of diffraction spots drops with increasing disorder. In order to be able to measure weak reflection spots, it is sometimes possible to increase the intensity of the X-rays used in the experiment, increase the exposure time or sensitivity of the detector, or increase the size of the crystals.
 ==Electron Density Map vs. Resolution==