The Calvin-Benson cycle, also known as the Calvin cycle or the carbon fixation cycle, is a series of chemical reactions that occur in the chloroplasts of green plants and algae. It is part of the process of photosynthesis, where organisms convert carbon dioxide and sunlight into glucose molecules, which can be used as an energy source for the cell.
The Calvin-Benson cycle involves three main stages:
1. Carbon Fixation: In this stage, carbon dioxide molecules from the atmosphere are incorporated into an organic molecule called ribulose-1,5-bisphosphate (RuBP), with the help of an enzyme called RuBisCO. This process forms an unstable six-carbon intermediate, which quickly breaks down into two molecules of a three-carbon compound called 3-phosphoglycerate (3PG).
2. Reduction: In this stage, ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate) molecules, which are produced during the light-dependent reactions of photosynthesis, are used to convert the 3PG molecules into another three-carbon compound called glyceraldehyde-3-phosphate (G3P). This step requires energy from ATP and reduces NADPH to NADP+.
3. Regeneration: In this final stage, some of the G3P molecules produced in the previous step are used to synthesize glucose, while others are used to regenerate the RuBP molecule so that the cycle can continue. The regeneration of RuBP requires ATP, which is produced during the light-dependent reactions.
Overall, the Calvin-Benson cycle uses energy from ATP and reducing power from NADPH to convert carbon dioxide into glucose, which can be stored for later use or used as a building block for other organic molecules in the plant. This cycle occurs in the stroma of the chloroplasts and is essential for the survival of plants and the production of oxygen as a byproduct.
CALVIN-BENSON CYCLE
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