In 1950, scientist Erwin Chargaff mentioned the principles about the structure of DNA through research called Chargaff’s rule. Scientist Chargaff found that the amount of Adenine and Thymine in the DNA molecule is equal. 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 pairs with C.