Question

Explain the phase – 3 of dark reaction.

Answer 1

Regeneration of RUBP involves the formation of several intermediate compounds of 6 – carbon, 5 – carbon, 4 – carbon and 7 – carbon skeleton. Fixation of one carbon dioxide requires 3 ATPs and 2 NADPH + H⁺ , and for the fixation of 6 CO₂ requires 18 ATPs and 12 NADPH + H⁺ during C₃ cycle. One 6 carbon compound is the net gain to form hexose sugar.

Overall equation for dark reaction: 

6CO₂ + 18 ATP + 12 NADPH + H⁺ → C₆ H₁₂ O₆ + 6H O + 18 ADP + 18 Pi + 12 NADP⁺