The enzymatic reactions of the Calvin cycle take place within the stroma of the chloroplast during photosynthesis. Although the Calvin cycle is sometimes also referred to as a dark reaction, this is a little misleading because the Calvin cycle indirectly relies on light. The cycle is named after Melvin Calvin, the scientist who discovered the reaction.
The Calvin cycle refers to the metabolic pathway found in plants, where carbon dioxide is processed to a carbohydrate. It plays a key role during photosynthesis. During this reaction, the cycle uses nicotinamide adenine dinucleotide phosphate, or NADPH2, for the electrons needed in making sugar, and adenosine triphosphate, or ATP, as a power source. The Calvin cycle is divided into three major stages: a carboxylation phase, reduction phase and regeneration phase.
During the carboxylation phase, carbon diffuses into the stroma of the plants, and it is then fixed by the carboxylation of the compound ribulose 1,5-biphosphate. This is followed by the reduction phase, where 3-phosphoglycerate is reduced to begin the synthesis of hexose sugar. In the final regeneration phase, the remaining sugar phosphate is converted to ribulose 1,5-biphospate so that the cycle can continue. Plants that utiilize the Calvin cycle in synthesizing foods are also referred to as C3 plants because a 3-carbon molecule is the first stable product of the reaction.