Calvin Cycle

Calvin Cycle

The Calvin Cycle is an essential part of photosynthesis, as it is the cycle that powers the formation of glucose for the plant. The Calvin Cycle occurs inside the chloroplasts of plant cells, specifically in the stroma. This cycle converts carbon dioxide, water, and sunlight into glucose and oxygen, which powers the plant and inevitably all animals above plants on the food chain. Chloroplasts use different types of chlorophyll, which are sensitive to different types of light to produce a variety of chemicals such as ATP, NADPH2, and more which power the Calvin Cycle. However, the cycle itself starts at the level of carbon dioxide. First carbon dioxide is incorporated into a five carbon sugar, ribulose bisphosphate (RuBP). Next this molecule is catalyzed by an enzyme (rubisco) to produce a six-carbon intermediate which immediately splits in half to form two molecules of 3-phosphoglycerate. Next ATP and NADPH2 from the light reactions are used to convert 3-phosphoglycerate to glyceraldehyde 3-phosphate, or G3P, the three-carbon carbohydrate precursor to glucose and other sugars. Finally, more ATP is used to convert some of the of the pool of G3P back to RuBP. For every three molecules of CO2 that enter the cycle, the net output is one molecule of glyceraldehyde 3-phosphate (G3P). For each G3P synthesized, the cycle spends nine molecules of ATP and six molecules of NADPH2. And for every two molecules off G3P synthesized one molecule of glucose is produced. The plant in the picture above uses this same process to create food from light.


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