In 1950, scientist Erwin Chargaff mentioned the principles about the structure of DNA through research called Chargaff’s rule. Scientist Chargaff found that DNA molecules have equal amounts of adenine and thymine. Again, the amounts of Guanine and Cytosine are also equal. This is called Chargaff principle. Half of the nitrogenous bases in the DNA molecule will be purines (A+G) and half will be pyrimidines (T+C). Hence A pairs with T and G with C.