Calvin Cycle

In-depth explanation of Calvin Cycle

The Calvin cycle is the light-independent stage of photosynthesis that fixes atmospheric CO2 into organic molecules in the chloroplast stroma. The enzyme RuBisCO attaches CO2 to ribulose-1,5-bisphosphate, producing two molecules of 3-phosphoglycerate. ATP and NADPH from the light reactions then reduce these to glyceraldehyde-3-phosphate, G3P, and most of the G3P regenerates RuBP so the cycle can continue. Three turns fix three CO2 and yield one net G3P, which can be used to make glucose and other carbohydrates. RuBisCO is slow and can also react with O2 in photorespiration, which reduces efficiency.

Going deeper: Calvin Cycle

Key ideas: In the stroma, Rubisco attaches CO2 to ribulose bisphosphate (5C), giving two 3-phosphoglycerate. Using ATP and NADPH these become G3P. Three turns fix 3 CO2 and yield one net G3P, using 9 ATP and 6 NADPH; making one glucose needs 6 turns, 18 ATP and 12 NADPH. Remaining G3P regenerates RuBP.

Common mistakes and connections: Mistake: calling it the dark reaction as if it works at night; it depends on light-made ATP and NADPH and several enzymes are light activated. Rubisco also binds O2 (photorespiration), wasting energy. Links to C4 plants and carbon fixation in the carbon cycle.

Visualization of Calvin Cycle

Three turns of the Calvin cycle fix 3 CO2 using 9 ATP and 6 NADPH to give one net G3P, the precursor of glucose. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Three CO2 molecules fixed over three turns yield one net G3P molecule for sugar synthesis.

Where Calvin Cycle fits in Biochemistry, Environment & Industry

Calvin Cycle is topic 38 of 127 in Biochemistry, Environment & Industry.

Related topics

• Oxidative PhosphorylationAdvanced
• PhotosynthesisBeginner
• Light ReactionsAdvanced
• Cellular RespirationIntermediate
• FermentationBeginner
• Digestion ChemistryIntermediate

Browse all 127 topics in Biochemistry, Environment & Industry