The process was first identified by American biochemist (Calvin, 1957).
The Calvin Cycle also known as the Calvin-Benson Cycle is a last step of photosynthesis, the process plants and other autotrophs use to create nutrients from sunlight and carbon dioxide.
It the cycle of chemical reactions plants go after to
Fix carbon from carbon dioxide into three-carbon sugars
Calvin Cycle Steps
It follows two stages
Light Reaction Phase: under the first phase, chemical reactions would use energy from light in order to produce NADPH and ATP. To build glucose light energy is converted into chemical energy.
Dark Reaction Phase: the second stage is the dark reaction phase, where water and carbon dioxide are converted into organic molecules. It does not signify that the Calvin Cycle only occurs in the dark, in this phase it just doesn’t need more light energy for the reactions to occur.
Reactions of Calvin Cycle
Carbon Fixation: The first stage in the cycle involve add in carbon from carbon dioxide into an organic molecule. In carbon fixation, a carbon dioxide molecule would muddle up with ribulose-1, 5-bisphosphate (RuBP), a five-carbon acceptor molecule.
Reduction: The reduction stage or second stage of the Calvin cycle requires ATP and NADP which are consumed to convert the 3-PGA molecules (which were taken from the carbon fixation stage) into a three carbon sugar identified as the glyceraldehyde-3-phosphate or G3P.
Regeneration: Under the regeneration stage, some G3P molecules would produce glucose and at the same time others would be recycled in order to regenerate the RuBP acceptor. This stage would call for ATP and involve a complex set of reactions.
Products of Calvin Cycle
In the main, the carbohydrate products of the Calvin cycle are the three carbon sugar phosphate molecules or the triose phosphates (G3P). The products produced after a single turn of the Calvin cycle are
- 3 ADP,
- Glyceraldehyde-3-phosphate (G3P) molecules and 2 NADP+.
- Protein (using nitrogen fixed from the soil)
- Lipids ( such as fats and oils)
In order to produce sugar (usually in the form of glucose or fructose), the Calvin cycle uses atmospheric carbon dioxide, ATP and NADPH (both produced in the light reactions) as reactants to create glyceraldehyde-3-phosphate (a 3-carbon sugar). Two glyceraldehyde-3-phosphate molecules can then be combined to create glucose or fructose (simple sugars). When ATP and NADPH are used in the Calvin cycle, they are released as ADP and NADP+. These molecules can then return to the light reactions where they can again be converted to ATP and NADPH using light energy.
Significance of Calvin Cycle
- The Significance of Calvin Cycle is as follows
- It is the main biochemical pathway during the dark reaction (Phase -II) of photosynthesis
- It results in the synthesis of carbohydrates from CO2 (assimilation of carbon).
- It depends on the light reaction (Phase-I) for the supply of the assimilatory power (ATP and NADPH2) required for carbon assimilation.
- It stores the ATP energy produced during light reaction in the carbohydrate molecules as the food energy.
- It is the prime source of organic food and food energy for all the organisms.
- Calvin Cycle(C-3 cycle) reaction take place in all photosynthetic plants i.e. C-3, C-4 and CAM plants, throughout the dark phase of photosynthesis.
The prime function of the Calvin Cycle is carbon fixation, which is making simple sugars from carbon dioxide. So the final product of Calvin cycle is Glucose.