Calvin cycle
The Calvin cycle is a light independent ("dark-reaction") process of carbon fixation that takes place in the chloroplasts of all plants, whether C3, C4, or CAM plants. The Calvin cycle utilizes light energy stored as ATP and NADPH to convert CO2 and H2O to organic compounds.
6 CO2 + 12 NADPH + 12 H+ + 18 ATP → C6H12O6 + 6 H2O + 12 NADP+ + 18 ADP + 18 Pi
Enzymes of the Calvin cycle are functionally equivalent to many enzymes involved in other metabolic pathways such as glycolysis and gluconeogenesis, but they are located in the chloroplast stroma rather than in the cytoplasm, thus functionally separating the reactions.
The enzymes are activated by light (hence light independent rather than "dark reaction") and by products of the light-dependent photosynthetic reactions. These regulatory mechanisms prevent the Calvin cycle from operating in reverse to respiration, thus preventing a continuous cycle of CO2 reduction to carbohydrates from occurring simultaneously with carbohydrate oxidation to CO2 (respiration). This regulation prevents the waste of energy (as ATP) in simultaneous reverse reactions that would have no net productivity.
Table ~ comparison photosynthesis & respiration : Table ~ comparison plant & bacterial photosynthesis : Table ~ comparison of C-3, C-4, CAM plants :
HOME • • Section Photosynthesis • Calvin cycle • C-3 • C-4 • CAM • Chloroplast • Chlorosomes • Cyanobacterial cell : cyclic photophosphorylation : • Light-reactions : noncyclic photophosphorylation : • Nonoxygenic photosynthesis • Oxygenic photosynthesis • Photosynthesis Overview • Photophosphorylation • Plant cell • Timeline • • Section Pigments • Antenna and Reaction Center • Bacteriochlorophylls • Carotenoids • Chlorophylls and accessory pigments • Pigments and absorption spectra • Phycobilins Section Articles • SITE MAP •
6 CO2 + 12 NADPH + 12 H+ + 18 ATP → C6H12O6 + 6 H2O + 12 NADP+ + 18 ADP + 18 Pi
Enzymes of the Calvin cycle are functionally equivalent to many enzymes involved in other metabolic pathways such as glycolysis and gluconeogenesis, but they are located in the chloroplast stroma rather than in the cytoplasm, thus functionally separating the reactions.
The enzymes are activated by light (hence light independent rather than "dark reaction") and by products of the light-dependent photosynthetic reactions. These regulatory mechanisms prevent the Calvin cycle from operating in reverse to respiration, thus preventing a continuous cycle of CO2 reduction to carbohydrates from occurring simultaneously with carbohydrate oxidation to CO2 (respiration). This regulation prevents the waste of energy (as ATP) in simultaneous reverse reactions that would have no net productivity.
Table ~ comparison photosynthesis & respiration : Table ~ comparison plant & bacterial photosynthesis : Table ~ comparison of C-3, C-4, CAM plants :
HOME • • Section Photosynthesis • Calvin cycle • C-3 • C-4 • CAM • Chloroplast • Chlorosomes • Cyanobacterial cell : cyclic photophosphorylation : • Light-reactions : noncyclic photophosphorylation : • Nonoxygenic photosynthesis • Oxygenic photosynthesis • Photosynthesis Overview • Photophosphorylation • Plant cell • Timeline • • Section Pigments • Antenna and Reaction Center • Bacteriochlorophylls • Carotenoids • Chlorophylls and accessory pigments • Pigments and absorption spectra • Phycobilins Section Articles • SITE MAP •
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