What is the calvin cycle?

The Calvin cycle, also known as the light-independent reactions, the dark reactions, or the photosynthetic carbon reduction (PCR) cycle, is a series of biochemical redox reactions that occur in the stroma of chloroplasts in photosynthetic organisms. It is part of the process of photosynthesis, specifically the second stage, following the light-dependent reactions.

The cycle uses the chemical energy generated by the <a href="https://www.wikiwhat.page/kavramlar/light-dependent%20reactions">light-dependent reactions</a> in the form of ATP and NADPH to fix carbon dioxide (CO2) and produce organic molecules, primarily <a href="https://www.wikiwhat.page/kavramlar/glucose">glucose</a>. It doesn't directly need light to occur.

Here's a breakdown of the key stages:

1. Carbon Fixation: CO2 is incorporated into an existing organic molecule, ribulose-1,5-bisphosphate (RuBP), with the help of the enzyme <a href="https://www.wikiwhat.page/kavramlar/RuBisCO">RuBisCO</a> (ribulose-1,5-bisphosphate carboxylase/oxygenase). This forms an unstable six-carbon compound that immediately breaks down into two molecules of 3-phosphoglycerate (3-PGA).

2. Reduction: 3-PGA is phosphorylated by ATP and then reduced by NADPH to form glyceraldehyde-3-phosphate (G3P), a three-carbon sugar. For every six CO2 molecules that enter the cycle, 12 molecules of G3P are produced.

3. Regeneration: Only two G3P molecules are used to produce glucose. The remaining ten G3P molecules are used to regenerate RuBP, allowing the cycle to continue. This regeneration requires ATP.

In summary, the Calvin cycle takes inorganic carbon (CO2) and uses ATP and NADPH to convert it into organic carbon (G3P), which can then be used to synthesize glucose and other organic molecules. The cycle is crucial for converting carbon dioxide into usable forms of energy for photosynthetic organisms.