How are X-ray crystal structures determined? 1. Grow crystals- structure determination by X-ray crystallography relies on the repeating structure of a crystalline lattice 2. Collect a diffraction pattern -periodically spaced atoms in the crystal give specific"spots"where X-rays interfere constructively 3. Carry out a Fourier transform to get from "reciprocal space"to a real space description of the electron density 4 THIS STEP REQUIRES KNOWLEDGE OF THE PHASES OF THE INTERFERING WAVES, WHICH CANT BE DIRECTLY MEASURED THE PHASE PROBLEM 4. Build a preliminary model of the protein into the envelope of electron density that results from the experiment 5. Refine the structure through an iterative process of changing the model and comparing how it fits the dataHow are X-ray crystal structures determined? 1. Grow crystals - structure determination by X-ray crystallography relies on the repeating structure of a crystalline lattice. 2. Collect a diffraction pattern - periodically spaced atoms in the crystal give specific “spots” where X-rays interfere constructively. 3. Carry out a Fourier transform to get from “reciprocal space” to a real space description of the electron density. 4. THIS STEP REQUIRES KNOWLEDGE OF THE PHASES OF THE INTERFERING WAVES, WHICH CAN’T BE DIRECTLY MEASURED “THE PHASE PROBLEM ” 4. Build a preliminary model of the protein into the envelope of electron density that results from the experiment. 5. Refine the structure through an iterative process of changing the model and comparing how it fits the data