Question

How many ATP and NADPH₂ are required for the synthesis of one molecule of Glucose during Calvin cycle?

• A. 18 ATP and 12 NADPH₂
• B. 12 ATP and 16 NADPH₂
• C. 18 ATP and 16 NADPH₂
• D. 12 ATP and 12 NADPH₂

Answer 1

The Correct Option is A

During the Calvin cycle, glucose is synthesized from carbon dioxide, requiring energy and reducing power. The Calvin cycle has three main stages: carbon fixation, reduction phase, and regeneration of ribulose bisphosphate (RuBP).

Each of these stages requires ATP and/or NADPH as follows: 

• Carbon fixation: CO₂ binds with ribulose bisphosphate (RuBP) and is catalyzed by the enzyme ribulose bisphosphate carboxylase-oxygenase (RuBisCO). For 6 CO₂ molecules, 12 molecules of 3-phosphoglycerate (3-PGA) are formed.
• Reduction phase: Each 3-PGA molecule is phosphorylated by ATP and then reduced by NADPH to form glyceraldehyde-3-phosphate (G3P). One glucose molecule formation requires 12 molecules of NADPH and 12 molecules of ATP at this step.
• Regeneration phase: ATP is needed to regenerate RuBP from G3P, allowing the cycle to continue. For the synthesis of one glucose molecule, an additional 6 ATP molecules are required at this step.

In total, for one glucose molecule: 12 ATP are used in the reduction phase and 6 ATP are used for RuBP regeneration, totaling to 18 ATP, while 12 NADPH are used in the reduction phase.

Therefore, the answer to how many ATP and NADPH₂ are required for the synthesis of one molecule of glucose during the Calvin cycle is:

18 ATP and 12 NADPH₂

Answer 2

The Calvin cycle, which is part of the light-independent reactions of photosynthesis, uses ATP and NADPH₂ (reduced form of NADP⁺) generated during the light-dependent reactions to fix carbon dioxide and produce glucose. Specifically, it takes 18 molecules of ATP and 12 molecules of NADPH₂ to synthesize one molecule of glucose.

Therefore, The correct option is (A): 18 ATP and 12 NADPH₂