Which compound is produced during regeneration? A. 3-PGA B. G3P C. RuBP D. rubisco
The Correct Answer and Explanation is:
The correct answer is C. RuBP (Ribulose bisphosphate).
During the regeneration phase of the Calvin cycle, RuBP is regenerated from G3P (Glyceraldehyde 3-phosphate). This phase involves a series of reactions that result in the restoration of RuBP, the molecule that combines with CO2 in the carboxylation phase of the cycle, enabling carbon fixation to continue.
Here’s a breakdown of how it works:
- G3P Production: In the earlier phases of the Calvin cycle (specifically the reduction phase), 3-PGA (3-phosphoglycerate) is converted into G3P through a series of reactions that require ATP and NADPH produced during the light reactions of photosynthesis.
- Regeneration of RuBP: In the regeneration phase, some of the G3P molecules are used to regenerate RuBP, which is essential for the cycle to continue. This process involves a complex series of reactions where G3P is reorganized and combined in different forms through the involvement of enzymes. The key enzyme in this step is ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), which is responsible for catalyzing the initial CO2 fixation reaction. However, RuBisCO itself is not the product of the regeneration phase; it’s the enzyme responsible for the carboxylation that produces RuBP.
- Energy Requirement: The regeneration of RuBP requires energy in the form of ATP. For every three molecules of CO2 that enter the cycle, five molecules of G3P are produced, and three of those molecules are used to regenerate RuBP.
Thus, the main product of the regeneration phase is RuBP, which enables the cycle to continue and capture more carbon dioxide. Without the regeneration of RuBP, the Calvin cycle would cease to function.
