pimeäreaktiossa

The pimeäreaktiossa, also known as the Calvin cycle or light-independent reactions, is a series of biochemical reactions that take place in the stroma of chloroplasts during photosynthesis. It is called the "dark reaction" because it does not directly require light, although it relies on the products of the light-dependent reactions (ATP and NADPH). The primary function of the pimeäreaktiossa is to convert atmospheric carbon dioxide into glucose, a sugar molecule that stores energy for the plant.

The cycle begins with carbon fixation, where an enzyme called RuBisCO attaches a molecule of carbon dioxide to a five-carbon sugar called RuBP (ribulose-1,5-bisphosphate). This unstable six-carbon compound quickly splits into two molecules of a three-carbon compound called 3-PGA (3-phosphoglycerate). In the next stage, reduction, ATP and NADPH from the light reactions are used to convert 3-PGA into G3P (glyceraldehyde-3-phosphate). Some of the G3P molecules are used to build glucose, while the rest are recycled to regenerate RuBP, allowing the cycle to continue. This regeneration process also requires ATP.

The Calvin cycle is a vital process for life on Earth, as it forms the basis of most food chains. The glucose produced is used by plants for growth and energy, and when herbivores consume plants, they obtain this stored energy. The cycle is a complex and elegant mechanism that effectively converts light energy into chemical energy in a stable form.