The linear order of N-bases hooked up to the sugar-phosphate backbone comprise the information storage system of the cell.
The N-bases can be divided into two classes of compound, the pyrimidines and the purines.
The pyrimidines are the simpler of the two, consisting of a single 'pyrimidine ring'.
There are three common pyrimidines,
Uracil (found exclusively in RNA),
Thymine (found exclusively in DNA) and
Cytosine (found in both RNA and DNA).
The numbering scheme for the pyrimidine ring and the structures of these N bases is shown below.
The purines are slightly more complex consisting of a pyrimidine ring fused to an imidazole ring as shown in figure 5. The purines consist of Adenine and Guanine, which are found in both RNA and DNA.
Figure 5:
Structure of the Purines
(H-bonding centers are indicated by arrows)
Figure 4:
Structure of the Pyrimidines
(H-bonding centers are indicated by an arrow)
