<Li> The enzyme RuBisCO catalyses the carboxylation of ribulose - 1, 5 - bisphosphate, RuBP, a 5 - carbon compound, by carbon dioxide (a total of 6 carbons) in a two - step reaction . The product of the first step is enediol - enzyme complex that can capture CO or O . Thus, enediol - enzyme complex is the real carboxylase / oxygenase . The CO that is captured by enediol in second step produces an unstable six - carbon compound called 2 - carboxy 3 - keto 1, 5 - biphosphoribotol (or 3 - keto - 2 - carboxyarabinitol 1, 5 - bisphosphate) that immediately splits into 2 molecules of 3 - phosphoglycerate, or 3 - PGA, a 3 - carbon compound (also: 3 - phosphoglyceric acid, PGA, 3PGA). </Li> <Li> The enzyme phosphoglycerate kinase catalyses the phosphorylation of 3 - PGA by ATP (which was produced in the light - dependent stage). 1, 3 - Bisphosphoglycerate (1, 3BPGA, glycerate - 1, 3 - bisphosphate) and ADP are the products . (However, note that two 3 - PGAs are produced for every CO that enters the cycle, so this step utilizes two ATP per CO fixed .) </Li> <Li> The enzyme glyceraldehyde 3 - phosphate dehydrogenase catalyses the reduction of 1, 3BPGA by NADPH (which is another product of the light - dependent stage). Glyceraldehyde 3 - phosphate (also called G3P, GP, TP, PGAL, GAP) is produced, and the NADPH itself is oxidized and becomes NADP . Again, two NADPH are utilized per CO fixed . </Li> <P> The next stage in the Calvin cycle is to regenerate RuBP . Five G3P molecules produce three RuBP molecules, using up three molecules of ATP . Since each CO molecule produces two G3P molecules, three CO molecules produce six G3P molecules, of which five are used to regenerate RuBP, leaving a net gain of one G3P molecule per three CO molecules (as would be expected from the number of carbon atoms involved). </P>

Where do light dependent and independent reactions occur