Pimeäreaktioissa

Pimeäreaktioissa, also known as the Calvin cycle or light-independent reactions, are a series of biochemical reactions that take place in the stroma of chloroplasts during photosynthesis. These reactions do not directly require light energy but rather utilize the ATP and NADPH produced during the light-dependent reactions. The primary function of the pimeäreaktioissa is to fix atmospheric carbon dioxide and convert it into glucose, a sugar molecule that serves as an energy source for the plant.

The cycle begins with carbon fixation, where the enzyme RuBisCO catalyzes the addition of CO2 to a five-carbon sugar called ribulose-1,5-bisphosphate (RuBP). This unstable six-carbon compound immediately splits into two molecules of a three-carbon compound, 3-phosphoglycerate (3-PGA). In the next phase, reduction, ATP and NADPH are used to convert 3-PGA into glyceraldehyde-3-phosphate (G3P), a three-carbon sugar. Some of these G3P molecules are then used to synthesize glucose and other organic molecules. The remaining G3P molecules are recycled in the final phase, regeneration, where ATP is consumed to convert them back into RuBP, allowing the cycle to continue.

Essentially, the pimeäreaktioissa takes the chemical energy captured during the light reactions and uses it to build sugars from carbon dioxide. This process is crucial for life on Earth as it forms the base of most food chains, providing the organic compounds that sustain virtually all organisms.