2. Complementary Base Pairing

• Scientist Chargaff found that the percentage of adenine and the percentage of thymine in a DNA molecule are the same. Likewise, percentage of cytosine and percentage of guanine are the same.

• Years later, it was proposed that the rule of complementary base pairing applies to the DNA.

• ie. Adenine found on one strand of polynucleotide would base pair with thymine on the opposite strand of polynucleotide and vice versa.

• Cytosine found on one strand of polynucleotide would base pair with guanine on the opposite strand of polynucleotide and vice versa.

Above: Rule of complementary base pairing occurs in the DNA molecule. Adenine on one polynucleotide base pairs with thymine on the opposite strand of polynucleotide and vice versa. Cytosine on one polynucleotide base pairs with guanine on the opposite strand of polynucleotide and vice versa.