Light-independent reactions take place in plant chloroplasts. In this process sugars are made from carbon dioxide. The process, known as the Calvin cycle, uses products of the light-dependent reactions (ATP and NADPH) and various enzymes. Therefore, the light-independent reaction cannot happen without the light-dependent reaction. Sugars made in the light-independent reactions are then moved around the plant by translocation.
The Calvin cycle[change | change source]
- A sugar (Ribulose biphosphate or RuBP) made of 5 carbon atoms combines with carbon dioxide to form a 6-carbon sugar (phosphoglycerate). An enzyme called RuBisCO speeds this reaction up.
- Phosphoglycerate is reduced with hydrogen atoms from the light-dependent reaction to form two molecules of triose phosphate (each has 3 carbon atoms). ATP is needed for this to happen.
- Some triose phosphate is converted (using ATP) back into Ribulose Biphosphate (which is why this is called a cycle).
- The rest left over is used to produce glucose.
The sum of reactions in the Calvin cycle is the following:
- 3 CO2 + 6 NADPH + 5 H2O + 9 ATP → glyceraldehyde-3-phosphate (G3P) + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi (Pi = inorganic phosphate)
Other websites[change | change source]
- The biochemistry of the Calvin cycle. Rensselaer Polytechnic Institute
- The Calvin cycle and the Pentose phosphate pathway from Berg J.M; Tymoczko J.L. & Stryer L. 2002. Biochemistry. 5th ed, W.H. Freeman.