1. Carbon Fixation:
* The cycle starts with the enzyme RuBisCo (ribulose-1,5-bisphosphate carboxylase/oxygenase) combining carbon dioxide with a 5-carbon sugar called ribulose-1,5-bisphosphate (RuBP).
* This forms an unstable 6-carbon molecule that quickly splits into two 3-carbon molecules called 3-phosphoglycerate.
2. Reduction:
* Each 3-phosphoglycerate molecule is phosphorylated by ATP, becoming 1,3-bisphosphoglycerate.
* NADPH then reduces 1,3-bisphosphoglycerate to glyceraldehyde-3-phosphate (G3P).
* G3P is a 3-carbon sugar and is the building block for glucose.
3. Regeneration:
* Most of the G3P produced is used to regenerate RuBP, allowing the cycle to continue.
* This involves a series of complex reactions, requiring ATP.
4. Glucose Production:
* For every 6 carbon dioxide molecules that enter the cycle, one molecule of glucose (a 6-carbon sugar) is produced.
* This glucose can be used for various purposes, such as energy production, building cell structures, or stored as starch.
Key Points:
* The Calvin cycle is a cyclical process, meaning the starting molecule (RuBP) is regenerated at the end of each cycle.
* It's a light-independent reaction, but it relies on the energy and reducing power produced during the light-dependent reactions.
* It is a complex process involving many enzymes and intermediate molecules.
In summary, the Calvin cycle uses energy from ATP and reducing power from NADPH to convert carbon dioxide into sugar (glucose). This process is essential for life on Earth, as it provides the primary source of energy and building materials for most organisms.
