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The material and molecular structure of a substance can often be inferred by quantitative study of this pattern. It is widely used in chemistry and biochemistry to determine the structures of an immense variety of molecules, including inorganic compounds, DNA and proteins. The first protein crystal structure was of sperm whale myoglobin, as determined by Max Perutz and Sir John Cowdery KendrewJohn Cowdery Kendrew ( March 24, 1917 August 23, 1997) was an English molecular biologist. He was born in Oxford, England, and was educated at the Dragon School in Oxford, as well as Clifton College in Bristol and Trinity College, Cambridge. John Kendrew in 1958, which led to a Nobel Prize in ChemistryList of Nobel Prize laureates in Chemistry from 1901 to the present day. 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s External link http://www. se/chemistry/laureates/i. The X-ray diffraction analysis of myoglobin was originally motivated by the observation of myoglobin crystals in dried pools of blood on the decks of whaling ships.

X-ray crystallography played a major role in elucidating the double-helix structure of DNA. See Rosalind FranklinRosalind Elsie Franklin ( July 25, 1920 April 16, 1958) was a molecular biologist who assisted in the discovery of the structure of DNA. Rosalind Franklin was born in London, England, and graduated from Cambridge University in 1941. Because of the ongoing, James D. WatsonJames Dewey Watson (born April 6, 1928) is one of the discoverers of the structure of the DNA molecule. Born in Chicago, Illinois, he enrolled at the age of 15, earned a B. in Zoology at the University of Chicago in 1947 and a Ph. in Zoology at Indiana Un, Francis CrickFrancis Harry Compton Crick OM ( June 8, 1916 July 28, 2004) was one of the discoverers of the structure of the DNA molecule. Born in Northampton, England, he studied physics at University College London, and became a B. During World War II, he worked on. Today X-ray crystallography is often used to determine how drugs, such as anti-cancer medications, can be improved to better influence their protein targets.

The molecule must be crystallized because one photon diffracted by one electron cannot be reliably detected. However, because of the regular crystalline structure, the photons are diffracted by corresponding electrons in many symmetrically arranged molecules. Because waves of the same frequency whose peaks match reinforce each other, the signal becomes detectable.

To determine a structure, one must first grow crystals of the molecule of interest using some method of crystallization. This can be a painstaking procedure for macromoleculeA macromolecule is a molecule composed of a very large number of atoms. But generally the use of term is restricted to molecules of more than 100 atoms, and in particular to polymers. Many examples come from biology and in particular biochemistry. These is such as protein and DNA complexes. The crystals are harvested and often frozen with liquid nitrogen. Freezing crystals both reduces radiation damage incurred during data collection and decreases thermal motion within the crystal. Crystals are placed on a diffractometer , a machine that emits a beam of x-rays. The x-rays diffract off the electrons in the crystal, and the pattern of diffraction is recorded on film and scanned into a computer. These diffraction images are combined and eventually used to construct a map of the electron density of the molecule that was crystallized, atoms are then fit to the electron density map and various parameters such as position are refined to best fit the observed diffraction data.

It is important to note that even after obtaining crystals suitable for diffraction analysis, current X-ray sources and detectors limit the measurement of only the diffracted photon intensities and not their respective phases, the latter encoding the majority of the information about the actual shape of electron density. A combination of experimental and computational methods are typically used to solve The Phase Problem , in order to estimate phases and obtain an initial map of the electron density.

After phases are esimated, a model made up of atoms is built and refined against the observed data. Once a model of a molecule's structure has been determined, it is often deposted in a crystallographic database such as the Protein Databank or the Cambridge Structure Database. Many structures obtained in private commercial ventures to crystallize medicinally relevant proteins, are not deposited in public crystallographic databases.

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