Structure and Properties of Purines and Pryimidines

Purines and pyrimidines are two of the building blocks of nucleic acids. Only two purines and three pyrimidines occur widely in nucleic acids. Here are their structures in organic chemists' line notation:

The Purines
Adenine   Guanine
The Pyrimidines
Cytosine Thymine Uracil

Crucial property: formation of hydrogen-bonded pairs composed of one purine and one pyrimidine, such as guanine-cytosine (left, below) and adenine-thymine (right).

Guanine-Cytosine Adenine-Thymine

Again, these equilibria involving the "abnormal" tautomers have relevance only for the individual pyrimidine in aqueous solution. The inter-base hydrogen bonds in the dimers strongly stabilize the structure indicated in the base pairs.

This page last modified 2:01 PM on Thursday December 18th, 2008.
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