jan 1, 1949 - Erwin Chargaff's discovery of the pattern of the nitrogenous bases of DNA

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Erwin Chargaff was an Austro-Hungarian-born American biochemist who graduated from the University of Vienna with a doctoral degree. In the 1940s, when Chargaff and many other biochemists made many discoveries, DNA was difficult to acquire, so the Chargaff experiment needed to find a way for determining the amount and type of material found in small quantities of DNA. Using a recently developed procedure involving paper chromatography, Chargaff used the photoelectric properties of the particles in DNA to identify the quantities of each base. First of all, Chargaff used paper chromatography to separate DNA into its constituent particles. Paper chromatography works by examining the rates at which different substances travel when exposed to a solvent. Differences in the distance traveled by each substance can be used to determine the identities of each component in a mixture. Next, Chargaff used mercuric nitrate to fix each of these separated particles as mercury salts. Finally, Chargaff used the amount of ultraviolet absorption to determine the amount of each nitrogenous base present in a sample. This formed the theory of fixed ratios and bases, which he soon discovered.

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