The bases, the building stones of the nucleic acids.

There are 4 + 1 bases, building stones for the nucleic acids. They compose the Desoxy Ribo Nucleic Acid (DNA) and the Oxy Ribo Nucleic Acid (RNA)

The double helix of DNA, schematically and in model:
In such a (super)macro molecule of DNA, the two very long helix chains go toghether (see figure). There is always that attraction between G and C, or A and T.


Inside the double helix, the molecules A, G, T, C e U participate in the bondings between the two strings of that double helix. (see figure).
Every bridge must deal with the same distance.
That is why A and G always combine with T, C and U