Carbon Atom Count and Molecule Quantity in the Calvin Cycle of Photosynthesis

Part A – Following carbon atoms around the Calvin cycleThe net reaction of the Calvin cycle is the conversion of CO2 into the three-carbon sugar G3P. Along the way, reactions rearrange carbon atoms among intermediate compounds and use the ATP and NADPH produced by the light reactions. In this exercise, you will track carbon atoms through the Calvin cycle as required for the net production of one molecule of G3P.For each intermediate compound in the Calvin cycle, identify the number of molecules of that intermediate and the total number of carbon atoms contained in those molecules. As an example, the output G3P is labeled for you: 1 molecule with a total of 3 carbon atoms.Labels may be used once, more than once, or not at all.

a. 3 molecules 3 carbonsb. 6 molecules 18 carbonsc. 6 molecules 18 carbonsd. 5 molecules 15 carbonse. 3 molecules 15 carbonsf. 3 molecules 15 carbons

Intermediate compound | Number of molecules | Total number of carbon atoms
— | — | —
CO2 | 6 molecules | 6 carbon atoms
3-PGA | 6 molecules | 18 carbon atoms
BPGA | 6 molecules | 18 carbon atoms
G3P | 1 molecule | 3 carbon atoms
RuBP | 5 molecules | 25 carbon atoms

Note: RuBP (ribulose-1,5-bisphosphate) is the molecule that initially reacts with CO2 in the Calvin cycle, but is also regenerated at the end. Hence, there are only 5 molecules of RuBP participating in the net production of one molecule of G3P.

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