Answered by The Community. Making the world better, one answer at a time. If the DNA macromolecule contains 20% G (guanine), then by Watson-Crick complementarity it must contain 20% C (cytosine). Together this equals 40%, so the percent that is A (adenine) and T (thymine) together is 60%.By Watson-Crick complementarity, then, the percent A in the molecule is half of 60: 30%.0 %. Adenine pairs with thymine-therefore if 20% is A, another 20% percent will be T. Only two other bases are left, which form pairs: guanine and cytosine, in equal quant … ities.