X-Ray Crytsallography Flashcards
What is a crystal?
- An arrangement of building blocks, which is periodic in three dimensions
- Very soft (needle test)
- Large solvent volume (20-80%)
- Mechanically fragile
- Exhibit birefringence (double refraction)
Why do we need a crystal?
- Periodic nature of crystals in 3D has unique properties
- Diffraction from individual atoms is additive, leading to good signal-to-noise in the X-ray experiment
Fluid Aggregate Model
Solubility curve for a protein
Factors affecting crystallisation of proteins
Crystallisation Method (Batch)
Crystallisation Method (Vapour Distillation)
Crystallisation Method (Dialysis)
Seeding Method
5 methods of Membrane Protein Crystallisation
3 types of Membrane Protein Crystals
Crystal quality ranking schemes
1) Clear
(2) oily droplets
(3) amorphous/gelatinous precipitate
(4) heavy precipitate
(5) Crystalline precipitate
(6) Needles/needle clusters
(7) Well formed, single crystals
Crystal Symmetry
7 Crystal systems
32 Classes, 14 Lattices, 230 Space Groups
14 Bravais Lattice
- A crystal is made up of this
periodic arrangement of one
or more atoms (the basis)
repeated at each lattice point
(or node). - Each node must have the same
number of neighbours, found
at same distances and
directions, and be in the same
environment.
Unit Cell + Asymmetric Unit
Unit Cell = smallest unit of volume that contains all of the structural and symmetry information and that by translation can reproduce a pattern in all of space
Asymmetric Unit = smallest unit of volume that contains all of the structural information and that by application of the symmetry operations can reproduce the unit cell
