1944 1950
ALD AVERY nearly 75 years following Miescher ' s overy , most scientists continued to believe protein , not DNA , was the carrier of hereditary mation .
changed in 1944 when biologist Oswald y performed a series of groundbreaking riments with a bacterial strain associated pneumonia . Avery had discovered that e alive but harmless form of the bacteria mixed with an inert but lethal form , the less bacteria would soon become deadly . ugh a series of experiments , Avery and his agues , Colin MacLeod and Maclyn McCarty , d that DNA , not protein , was the substance onsible for transforming the bacteria . They luded that something about DNA allowed carry instructions from one cell to another . r conclusions highlighted DNA as the sforming factor '.
ERWIN CHARGAFF
Following a read of Avery ’ s 1944 scientific paper identifying DNA as the substance responsible for heredity , scientist Erwin Chargaff began studying the chemistry of nucleic acids and devised a method of analyzing the nitrogenous components and sugars of DNA .
Chargaff was able to rapidly analyze DNA from a wide range of species and in 1950 , he reported two major findings , now regarded as ' Chargaff ’ s Rules ', regarding the chemistry of nucleic acids : 1 . In any double-stranded DNA , the number of guanine units equals the number of cytosine units and the number of adenine units equals the number of thymine units . 2 . The composition of DNA varies between species .