Adenine

The flavour of life, of living things on earth, might be seen as an expression of the organic compound "adenine". The molecule adenine is central to all life functions providing the basis for energy exchange, communication (signaling), reproduction and the specification of chemical forms through the DNA's templating of proteins. Life is an elaboration of adenine. Adenine determines the style of life on this planet (and probably elsewhere).
Adenine is a purine, a cyclic nitrogenous organic compound, with an extra amine added(at "sixth" carbon). Biologically it becomes useful (indeed, ubiquitous) after a sugar, ribose or deoxyribose, is added on to make the "nucleoside" adenosine. In most of its forms phosphate ions are appended to the pentose sugar and so we get adenosine monophosphate, AMP, adenosine diphosphate, ADP,and adenosine triphosphate, ATP. Now, flipping back and forth between ADP and ATP is the way living things utilize energy. ATP is the universal "coin" of energy in all living system!

There is a point of interest here about magnitudes. The energy involved in binding the first phosphate ion to the sugar is greater than that binding the second ion to the AMP, and that is greater than the energy binding the third phosphate ion to the ADP. The energy involved in turning ADP to ATP is small and it is just that, that moderateness of the energy, that makes it useful, that makes it the universal coin.

Adenosine is also the molecule upon which DNA and RNA are elaborated. In RNA the parings adenine and guanine are paired with the pyrimidines cytosine and uracil. (In DNA adenine pairs with thymine)

                   

and stringing these "base-pairs" together
we get RNA and our helical DNA

We might look at the base pairs as adenine and not adenine (guanine), and purines and not purines (pyrimidines) and in this sense it is all adenine and not adenine.

So adenine is the energy for the cell, information for the cell (both to structure proteins and for reproduction) and it is also used as the most basic signaling process in the cell. AMP, adenosine monophosphate can curl up (and bite its tail) to become cyclic AMP.

and cyclic AMP (cAMP) is used as a primary signal within cells.

And so, in a sense, adenine is the seed from which life is styled on this planet, and it may be that adenine is not chosen at random but that it is intrinsically the most stable and useful purine, in which case we might expect that much of life throughout the cosmos is elaborated on ATP, cAMP and DNA.