Why do purines pair with pyrimidines?

I know that adenine bonds with thymine and guanine bonds with cytosine (known as the base pair rule). It also has to do with DNA.


-Purines are adenine and guanine nitrogen bases.
-Pyrimidines are thymine and cytosine nitrogen bases.

1 Answer
Dec 9, 2016

Dictated by specific hydrogen bonding patterns ,base pairs between Guanine (G) - Cytosine (C) and Adenine (A) - Thymine (T) , allow the DNA helix to maintain a regular helical structure.


Pairing of a specific purine to a pyrimidine is due to the structure and properties of these bases. A and G are purines and T and C are pyrimdines. In DNA base pairing, A pairs with T and C with G.

Matching base pairs ( purines and pyrimidines ) form hydrogen bonds. A and T have two sites where they form hydrogen bonds to each other. C and G have three sites.

Bonded together , these base pairs form the rungs of the DNA ladder or double helix.

For each of the four nitrogenous bases a specific tautomeric form must be incorporated for proper bonding , stability and attachment to the sugar phosphate backbone of DNA.