·        Precursors of DNA and RNA.

·        Activated intermediates in many biosyntheses: e.g UDP-glucose ® glycogen, CDP-diacylglycerol ® phosphoglycerides, S-adenosylmathionine as methyl donor, etc.

·        Nucleotside triphosphates, especially ATP, as the universal currency of energy in biological systems.

·        Adenine nucleotides are components of the coenzymes, NAD(P)+, FAD, and CoA.

·        Metabolic regulators:  (a) c-AMP is the mediator of hormonal actions; (b) ATP-dependent protein phosphorylation - activates phosphorylase and inactivates glycogen synthase; (c) adenylation of a Tyr of bacterial glutamine synthetase - more sensitive to feedback inhibition and less active; (d) allosteric regulator - glycogen phosphorylase activated by ATP and inactivated by AMP.