Regeneration of RuBP

Out of every 12 molecules of 3-phosphoglyceraldehyde (3-PGAL) produced in one turn of the cycle (from fixing 6 CO2 onto 6 RuBP), only 2 are drawn off to build a single molecule of glucose; the remaining 10 are used, through a further series of complex reactions consuming 6 more ATP, to regenerate the 6 molecules of RuBP the cycle needs to keep accepting fresh CO2. Because only 2 of the 12 three-carbon units go toward the eventual glucose, six complete turns of the Calvin cycle (fixing a total of 6 CO2 each time, so 36 CO2 overall) are required to accumulate one molecule of glucose. Through these repeated reactions, the pl …