Step 3 Most of PGAL is converted back into RUBP in a complicated series of reactions which require a phosphate group from ATP (becomes ADP) allows Calvin cycle to continue However, some PGAL is not converted back into RUBP and leaves the cycle to be used by the plant to produce organic compounds In short: 2 PGALs release CH2O and form RUBP to be used again. Some PGAL leaves the cycle