BCH3052 Lecture Notes - Lecture 4: Atomic-Force Microscopy, Synchrotron Radiation, Electromagnetic Radiation
25 May 2018
School
Department
Course
Professor
Lecture 5 – Introduction to X-ray Crystallography
Protein Structure Determination using X-ray Crystallography
• Calculate electron density map to build atomic model
Crystallography
• Shine X-ray on crystal → record diffraction pattern → derive
phases → build trace protein into electron
o Each reflection: can measure intensity (how dark it is) and
where it is
o Phase angle
• Detecting how electrons are scattered in the molecule
Why do we Use X-rays?
• For the resolution required
• 1 Angstrom of wavelength = 1x10-10meter
• Electromagnetic radiation with wavelength on order of bond lengths
• Allows us to see atoms where it wouldn’t be possible under visible light
How to Make X-rays?
1. In-house source: fire electrons at a metal target
• Anode: made of copper and spins
o Electrons hit copper → knock into a higher energy level →
release energy as heat and converted into x-rays
• Cathode
2. Use a synchrotron
• Electrons using very small charges that are moving really fast
o Synchrotron radiation is generated by the radial acceleration of
electrons to ultraelativisitic speed through magnetic fields
• Properties
o Produces incredibly intense light (high britness)
o Tunable: can alter the wavelengths
• Generate electrons → linear accelerator and booster ring
• Transferred to outer storage ring → give our very intense light → use for
x-rays
Why do we Need Crystals?
• So we can measure diffraction
• The repeating lattice of a crystal give rise to diffraction when X-ray are shined
on it
• Large solvent channels within crystals → makes them very fragile
• Can image surface of a crystal using Atomic force microscopy
• A single molecule will scatter electrons – BUT unable to measure the
scattering due to the signals being too weak
• Repeating pattern of molecules causes the scattered X-rays to diffract
o Amplifies the scattering of X-rays
How to Make Crystals?
• Hanging Drop Vapour Diffusion Method
o Precipitant at bottom
find more resources at oneclass.com
find more resources at oneclass.com
