The Calvin Cycle, also known as the Calvin-Benson-Bassham CBB cycle, is a set of light-independent reactions that occur during photosynthesis in the chloroplasts of plants, algae, and some bacteria. The primary function of the Calvin Cycle is to fix atmospheric CO2 into organic molecules, ultimately producing glucose and other sugars that can be used by the organism for energy and growth.The Calvin Cycle consists of three main stages: carbon fixation, reduction, and regeneration of the starting molecule ribulose-1,5-bisphosphate RuBP . Here's a detailed overview of the process:1. Carbon fixation: The enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase RuBisCO catalyzes the reaction between CO2 and ribulose-1,5-bisphosphate RuBP , a 5-carbon sugar. This reaction results in an unstable 6-carbon intermediate, which quickly breaks down into two molecules of 3-phosphoglycerate 3-PGA , a 3-carbon compound.2. Reduction: The 3-PGA molecules undergo a series of reactions to be converted into glyceraldehyde-3-phosphate G3P , a high-energy 3-carbon sugar. First, 3-PGA is phosphorylated by ATP, forming 1,3-bisphosphoglycerate 1,3-BPG . Then, the enzyme glyceraldehyde-3-phosphate dehydrogenase GAPDH reduces 1,3-BPG to G3P using NADPH as a reducing agent. Both ATP and NADPH are products of the light-dependent reactions of photosynthesis.3. Regeneration of RuBP: The majority of G3P molecules produced in the reduction stage are used to regenerate RuBP, allowing the cycle to continue. This process involves a complex series of enzymatic reactions, including those catalyzed by triose phosphate isomerase TPI , aldolase, fructose-1,6-bisphosphatase FBPase , transketolase, and ribulose-5-phosphate kinase Ru5PK . These reactions rearrange the carbon skeletons of G3P and other intermediates to produce RuBP, which can then re-enter the cycle and fix more CO2.For every three turns of the Calvin Cycle, one G3P molecule is produced as an output, while the other five G3P molecules are used to regenerate RuBP. Two G3P molecules can be combined to form one glucose molecule, so six turns of the cycle are required to produce one glucose molecule.In summary, the Calvin Cycle uses carbon fixation to convert atmospheric CO2 into organic molecules through a series of enzyme-catalyzed reactions. The key enzyme involved in carbon fixation is RuBisCO, which combines CO2 with RuBP. The cycle then proceeds through reduction and regeneration stages, ultimately producing G3P, which can be used to synthesize glucose and other organic molecules.