Why do purines pair with pyrimidines?

1 Answer
Apr 21, 2016

Purines pair with pyrimidines because their size and shape make them a perfect fit for hydrogen bonding


Purines and pyrimidines are base pairs.

The two most common base pairs are A-T and C-G.


These nucleotides are complementary —their shape allows them to bond together with hydrogen bonds.

In the A-T pair, the purine (adenine) has two binding sites, and so does the pyrimidine (thymine)

In the C-G pair, the purine (guanine) has three binding sites, and so does the pyrimidine (cytosine).

The hydrogen bonding between complementary bases is what holds the two strands of DNA together.