Calvincirklo

Calvincirklo, also known as the Calvin Cycle, is a series of biochemical reactions that take place in the stroma of chloroplasts in photosynthetic organisms. It is the primary pathway for the fixation of carbon dioxide into organic compounds. The cycle does not directly require light, hence it is also referred to as the light-independent reactions of photosynthesis.

The Calvin Cycle begins with the enzyme RuBisCO catalyzing the carboxylation of ribulose-1,5-bisphosphate (RuBP) with carbon dioxide. This results in an unstable six-carbon intermediate that immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA). In the next stage, ATP and NADPH, produced during the light-dependent reactions, are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P). G3P is a three-carbon sugar that serves as the building block for glucose and other organic molecules.

For every three molecules of CO2 that enter the cycle, one molecule of G3P is produced as a net output. The remaining G3P molecules are used to regenerate RuBP, allowing the cycle to continue. This regeneration process also consumes ATP. The Calvin Cycle is essential for converting inorganic carbon into organic matter, forming the base of most food chains on Earth. It is a fundamental process in plant physiology and the global carbon cycle.