ound ▁in ▁the ▁path way ▁to ▁have ▁a ▁completely ▁formed ▁pur ine ▁ring ▁system . ▁ ▁I MP ▁ ▁In os ine ▁mon oph osph ate ▁is ▁synth es ized ▁on ▁a ▁pre - ex isting ▁rib ose - ph osph ate ▁through ▁a ▁complex ▁path way ▁( as ▁shown ▁in ▁the ▁figure ▁on ▁the ▁right ). ▁The ▁source ▁of ▁the ▁carbon ▁and ▁nit ro gen ▁atoms ▁of ▁the ▁pur ine ▁ring , ▁ 5 ▁and ▁ 4 ▁respectively , ▁come ▁from ▁multiple ▁sources . ▁The ▁am ino ▁acid ▁g ly c ine ▁cont ributes ▁all ▁its ▁carbon ▁( 2 ) ▁and ▁nit ro gen ▁( 1 ) ▁atoms , ▁with ▁additional ▁nit ro gen ▁atoms ▁from ▁gl ut am ine ▁( 2 ) ▁and ▁as part ic ▁acid ▁( 1 ), ▁and ▁additional ▁carbon ▁atoms ▁from ▁form yl ▁groups ▁( 2 ), ▁which ▁are ▁transferred ▁from ▁the ▁co enz yme ▁t et rah ydro fol ate ▁as ▁ 1 0 - form y lt et rah ydro fol ate , ▁and ▁a ▁carbon ▁atom ▁from ▁b ic ar bon ate ▁( 1 ). ▁Form yl ▁groups ▁build ▁carbon - 2 ▁and ▁carbon - 8 ▁in ▁the ▁pur ine ▁ring ▁system , ▁which ▁are ▁the ▁ones ▁acting ▁as ▁brid ges ▁between ▁two ▁nit ro gen ▁atoms . ▁ ▁A ▁key ▁regul atory ▁step ▁is ▁the ▁production ▁of ▁ 5 - ph osph o - α - D - rib os yl ▁ 1 - py roph osph ate ▁( PR PP ) ▁by