Calvin Cycle
Calvin Cycle: It is the second stage in Photosynthesis that involes CO2 fixation and reduction of the carbon into carbohydrate/sugar.
1. One Carbon atom, from CO2, enters and attaches itself to a five Carbon molecule called Ribulose Bisphosphate (RuBP) with the help from an enzyme called RuBP carboxylase, Rubisco.
2. The six Carbon molecule is very unstable so it splits into two three carbon molecules. The molecule is called 3-Phosphoglycerate. Each molecule has a Phosphate.
3. Each molecule of 3–phosphoglycerate receives an additional phosphate group from ATP, becoming 1,3–bisphosphoglycerate.
4. Then a pair of electrons from NADPH reduces 1,3–bisphosphoglycerate to G3P. (The electrons from NADPH reduce the carboyxl group of 3–phosphoglycerate to the aldehyde group of G3P, which stores more potential energy).
5. G3P is commonly known as sugar. It is the same product formed in glycolysis by splitting glucose.
6. Only one Carbon exits the cycle as sugar. Other five Carbons are recycled to regenerate the three molecules of RuBP.
7. The Carbon skeletons of five carbon molecules of G3P are rearranged at the last steps of the Calvin cycle into three molecules of RuBP. This action requires energy. The cycle uses three molecules of ATP (energy).
8. Cycle continues.
See how well you know Calvin Cycle by taking the quiz below:)
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