Chargaff's rules state that DNA from any cell of all organisms should have a 1:1 ratio (base Pair Rule) of pyrimidine and purine bases and, more specifically, that the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine.
In this way, why adenine Cannot bond with guanine?
Adenine can't pair with Guanine because: Both are too large and would cause the double helix to bend out of shape. Even if they tried to pair, the hydrogen bonds wouldn't be strong enough to resist the mechanical stress caused by their size.
Why adenine and guanine are called purines?
The single-ring nitrogenous bases, thymine and cytosine, are called pyrimidines, and the double-ring bases, adenine and guanine, are called purines. (Miss Crimson has a puzzled look.) Adenine and guanine are purines.
What does guanine always bond with?
The chemistry of the nitrogenous bases is really the key to the function of DNA. It allows something called complementary base pairing. You see, cytosine can form three hydrogen bonds with guanine, and adenine can form two hydrogen bonds with thymine. C will only bond with G and A will only bond with T in DNA.