WHAT IS HAPPENING IN THE REGENERATION PHASE OF CALVIN BENSON CYCLE
During the regeneration phase of the Calvin Benson cycle, the process of the synthesis of glucose occurs. This phase involves the regeneration of the starting molecule, ribulose-1,5-bisphosphate (RuBP), which is necessary for the continuation of the cycle. The steps involved in the regeneration phase can be summarized as follows:
1. 3-phosphoglycerate (3-PGA), the product of the carbon fixation phase of the Calvin Benson cycle, is converted into 1,3-bisphosphoglycerate (1,3-BPGA) by utilizing ATP.
2. 1,3-BPGA is then reduced to glyceraldehyde-3-phosphate (G3P) by utilizing NADPH. For every three molecules of CO2 that are fixed, six molecules of G3P are produced.
3. Out of the six molecules of G3P produced, one molecule exits the cycle to be used for the synthesis of glucose or other organic molecules. The remaining five molecules of G3P undergo a series of enzymatic reactions, ultimately leading to the regeneration of three molecules of RuBP.
4. The conversion of G3P to RuBP requires an input of ATP. The exact steps involved in the regeneration phase may vary depending on the plant species and environmental conditions.
Overall, the regeneration phase of the Calvin Benson cycle ensures the continuous flow of carbon dioxide fixation and glucose synthesis, which are essential for sustaining plant growth and metabolism.
During the regeneration phase of the Calvin Benson cycle, several key reactions occur to replenish and regenerate the molecules needed for carbon fixation to continue. Here are the steps involved:
1. Formation of Ribulose 1,5-Bisphosphate (RuBP): In this step, Ribulose 5-Phosphate, generated during the carbon fixation phase, is phosphorylated by ATP to form RuBP. The enzyme responsible for this reaction is Ribulose-5-phosphate kinase.
2. Cleavage of 6-Carbon Molecule: RuBP is an unstable compound that quickly breaks down into two 3-phosphoglycerate (PGA) molecules. This process is catalyzed by the enzyme Ribulose Bisphosphate Carboxylase/Oxygenase (RuBisCO).
3. Reduction of 3-Phosphoglycerate (PGA) to Glyceraldehyde 3-Phosphate (G3P): The PGA molecules are then reduced, using energy from ATP and electrons from NADPH, to form glyceraldehyde 3-phosphate (G3P). The enzyme responsible for this reduction is 3-Phosphoglycerate kinase.
4. Regeneration of Ribulose 5-Phosphate: Some of the G3P molecules formed in the previous step are converted back into RuBP. This process requires ATP and involves a series of enzymatic reactions, including epimerization and rearrangement.
5. Exit of G3P: Some of the G3P molecules formed in the Calvin Benson cycle are utilized for the synthesis of glucose and other carbohydrates, while others are recycled back into the cycle to regenerate RuBP.
Overall, the regeneration phase of the Calvin Benson cycle ensures that the necessary molecules, particularly RuBP, are continuously replenished to sustain the cycle and allow for continuous carbon fixation and subsequent carbohydrate synthesis.