1.Chargaffs Rules
1. Base composition of DNA differs from species to species
2. In each species, however, the # of adenine (a) equals the # of thymine (T).
Also # of G = # of C
3. sum of purines (A+G) = sum of pyrimidines (T+C)
2. Complementary Base Pairing
-purines = pyrimidines Total purines [A]+[G] = Total pyrimidines [C]+[T]
-concentration of adenine and thymine are equal as are guanine and cytosine.
the ratio of A+T:C+G does not necessarily equal one (note this point)
Therefore, A pairs with T and C pairs with G in DNA
the thymine - adenine pair interacts through two hydrogen bonds represented as (T=A) and that the cytosine-guanine pair interacts through three hydrogen bonds represented as (C=G).
therefore,A+T=C+G is incorrect
Hope this helps,