1. Carboxylation
(i) Ribulose 1, 5 bisphosphate reacts with atmospheric CO2 to produce 6-carbon (C6) keto acids under the action of rubisco enzyme. Keto acid is rapidly broken down to 3-phosphoglyceric acid. (RuBisCO is the most important enzyme in the world)
2. Phosphorylation
(ii) 3-phosphoglyceric acid is converted to 1,3-bisphosphoglyceric acid with the help of the enzyme phosphoglycerokinase. At this time, ATP takes part in the reaction and produces ADP.
3. Reduction
(iii) Phosphoglyceraldehyde dehydrogenase enzyme produces 3-phosphoglyceraldehyde and dihydroxyacetone phosphate from 1,3 bisphosphoglyceric acid. At this time, NADPH+H+ takes part in the reaction to form NADP.
4. Carbohydrate production
(iv) Fructose 1, 6 bisphosphate is produced from 3-phosphoglyceraldehyde by the action of aldolase enzyme.
(v) Fructose 1, 6 bisphosphate is converted to fructose 6-phosphate in the presence of phosphofructokinase enzyme. During this reaction, ADP takes part and produces ATP.
(vi) Glucose 6-phosphate is produced from fructose 6-phosphate under the action of phosphoglucoisomerase enzyme.
(vii) Glucose is produced from glucose 6-phosphate under the action of hexokinase enzyme. At this time, ADP takes part in the reaction to form ATP.
5. Regeneration of RuBP
(viii) 3-phosphoglyceraldehyde reacts with fructose 1,6 bisphosphate to produce ribulose 5 phosphate.
(ix) Ribulose 1, 5-bisphosphate is produced from ribulose 5-phosphate. Ribulose 1, 5 bisphosphate re-enters the Calvin-Basham cycle and keeps the cycle going.