How many molecules of ATP and NADPH are required for every molecule of CO2 fixed in the Calvin cycle?
- 2 molecules of ATP and 3 molecules of NADPH
- 2 molecules of ATP and 2 molecules of NADPH
- 3 molecules of ATP and 3 molecules of NADPH
- 3 molecules of ATP and 2 molecules of NADPH
Answer
(4) 3 molecules of ATP and 2 molecules of NADPH
Solution
In the Calvin cycle, fixing one molecule of CO2 uses 2 ATP in reduction (2 molecules of 3-PGA → 2 G3P) and 1 ATP in regeneration of RuBP, i.e. 3 ATP in all.
The reduction step also uses 2 NADPH.
So every CO2 fixed needs 3 ATP and 2 NADPH (for one glucose: 18 ATP and 12 NADPH).
Answer: (4)