Question

Give an account on energetics of Calvin cycle.

Answer 1

Calvin cycle, also known as C3-cycle is the process that occurs during the dark reaction of the photosynthesis. In this process, CO${}_2$ is accepted by RuBP (Ribulose-1,5-bisphosphate) in the presence of an enzyme called Rubisco (RuBP carboxylase/oxygenase). The ATPs and NADPH generated during the Light-Reaction are consumed in this process. The whole cycle can be divided into following three phases:

1. Carbon fixation: CO${}_2$ combines with RuBP to form 6 carbon intermediate that breaks into two 3 carbon compound called phosphoglyceric acid.

2. Reduction: Phosphoglyceric acid is reduced to Glyceraldehyde-3-phosphate in the presence of ATP and NADPH. Total consumption of 6 ATP and 6 NADPH occurs in this phase.

3. Regeneration of RuBP: Some Glyceraldehyde-3-Phosphate are used in regeneration of RuBP. This phase consumes 3 ATP.