<P> The regeneration stage can be broken down into steps . </P> <Ol> <Li> Triose phosphate isomerase converts all of the G3P reversibly into dihydroxyacetone phosphate (DHAP), also a 3 - carbon molecule . </Li> <Li> Aldolase and fructose - 1, 6 - bisphosphatase convert a G3P and a DHAP into fructose 6 - phosphate (6C). A phosphate ion is lost into solution . </Li> <Li> Then fixation of another CO 2 generates two more G3P . </Li> <Li> F6P has two carbons removed by transketolase, giving erythrose - 4 - phosphate . The two carbons on transketolase are added to a G3P, giving the ketose xylulose - 5 - phosphate (Xu5P). </Li> <Li> E4P and a DHAP (formed from one of the G3P from the second CO 2 fixation) are converted into sedoheptulose - 1, 7 - bisphosphate (7C) by aldolase enzyme . </Li> <Li> Sedoheptulose - 1, 7 - bisphosphatase (one of only three enzymes of the Calvin cycle that are unique to plants) cleaves sedoheptulose - 1, 7 - bisphosphate into sedoheptulose - 7 - phosphate, releasing an inorganic phosphate ion into solution . </Li> <Li> Fixation of a third CO 2 generates two more G3P . The ketose S7P has two carbons removed by transketolase, giving ribose - 5 - phosphate (R5P), and the two carbons remaining on transketolase are transferred to one of the G3P, giving another Xu5P . This leaves one G3P as the product of fixation of 3 CO 2, with generation of three pentoses that can be converted to Ru5P . </Li> <Li> R5P is converted into ribulose - 5 - phosphate (Ru5P, RuP) by phosphopentose isomerase . Xu5P is converted into RuP by phosphopentose epimerase . </Li> <Li> Finally, phosphoribulokinase (another plant - unique enzyme of the pathway) phosphorylates RuP into RuBP, ribulose - 1, 5 - bisphosphate, completing the Calvin cycle . This requires the input of one ATP . </Li> </Ol> <Li> Triose phosphate isomerase converts all of the G3P reversibly into dihydroxyacetone phosphate (DHAP), also a 3 - carbon molecule . </Li> <Li> Aldolase and fructose - 1, 6 - bisphosphatase convert a G3P and a DHAP into fructose 6 - phosphate (6C). A phosphate ion is lost into solution . </Li>

What part of a chloroplast does the calvin cycle occur in