What are purines?

Purines are similar in chemical composition and are comprised of either guanosine or adenosine which can exist in nucleoside or nucleotide form.  The nucleotide form may be mono, di, tri-phosphorylated or cyclic in nature as exampled below.

Purinergic Signalling

The number of phosphates groups on the molecule denotes if it is mono (one), di (two), or tri (three) phosphorylated as shown here:

http://www.uni-leipzig.de/~straeter/research/ntpdase.html

http://www.nature.com/aps/journal/v31/n9/fig_tab/aps2010128f1.html

http://www.nature.com/nri/journal/v11/n3/fig_tab/nri2938_F1.html#figure-title

http://www.nature.com/cddis/journal/v1/n1/fig_tab/cddis200911f5.html

http://www.nature.com/cddis/journal/v1/n1/fig_tab/cddis200911f4.html

https://www.qiagen.com/geneglobe/pathwayview.aspx?pathwayID=336

http://jpet.aspetjournals.org/content/295/3/862.full

http://physiologyonline.physiology.org/content/18/1/12.full

http://www.brainimmune.com/mockup/index.php?option=com_content&view=article&id=348:regulation-of-t-helper-cell-function-by-extracellular-atp&catid=78:neurohormonal-regulation-of-immunity&Itemid=421

http://www.synapses.co.uk/genetics/tsg19.html