Why do purines and purines do not pair?

Question

Why do purines and purines do not pair?

Answer 1

Purines cannot pair with purines, the whole spacing qould be messed up. There would be many variations in the DNA's shape. This would completely destroy the structure. Not to mention the hydrogen bond sites, which must be matched exactly.

Answer 2

purines are AG while pyrimidines are GC.these donot interact with each other because of steric hinderance of the molecule.by pairing the DNA will get denatured and damaged.there will be a bend in DNA stucture and all the activities occured in DNA will be hindered and prevented.the  phosphodiester bonds in strand will also be affected.

Answer 3

The fact is purines CAN pair with purines in non-conventional pairing systems (ie: not the AT CG Watson-Crick pairings that we are all taught).

Within the Watson-Crick system, the reason purines do not pair with purines is because of the overall structure of DNA. A purine-purine base pair is larger than a purine-pyrimidine base pair and disrupts the overall structure of the DNA helix (at least locally). This has larger impacts on the stability of the molecule and also its ability to be scanned, repaired, and replicated by the cellular machinery.

One of the reasons Watson and Crick figured out that it had to be a purine-pyrimidine base pairing system was because of the X-ray crystallographic data solved by Rosalind Franklin.

Answer 4

Their structure is not complementary to each other

Answer 5

Structure is different so purine  & Pyramidines are not pairing, Pairing occurs when there is a mutation.