The different types of nitrogen containing bases


The following four compounds are the nitrogen containing bases.
(click on them to see, better, their structures, with animations):

Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)

Adenine (A) pairs with Thymine (T), while Cytosine (C) pairs with Guanine (G). The amount of the bases in the global structure is well defined:

it is always (A)=(T) and (G)=(C), hence (A)+(C)=(G)+(T) .