Adenosine is one of the building blocks of nucleic acids.
Adenosine is produced by an adenine binding to a nitrogen base and a ribose (in RNA) or a deoxyribose (in DNA). Adenosine can be bound to phosphate groups. In this case we refer to adenosine monophosphate (AMP), adenosine diphosphate (ADP), or adenosine triphosphate (ATP).
In particular, ATP is an energy-containing molecule that releases energy by hydrolysing a phosphodiester bond.
Cyclic AMP (cAMP) is also a special molecule, as it acts as a switch in intracellular transmission.
Adenosine is also a hormonal neurotransmitter.
Adenosine is adenine bound to a ribose. © Wikimedia, public domain