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Calvin cycle step 1 (black circles represent carbon atoms) Calvin cycle steps 2 and 3 combined. The enzyme RuBisCO catalyses the carboxylation of ribulose-1,5-bisphosphate, RuBP, a 5-carbon compound, by carbon dioxide (a total of 6 carbons) in a two-step reaction. [6] The product of the first step is enediol-enzyme complex that can capture CO 2 ...
C 3 carbon fixation occurs in all plants as the first step of the Calvin–Benson cycle. (In C 4 and CAM plants, carbon dioxide is drawn out of malate and into this reaction rather than directly from the air.) Cross section of a C 3 plant, specifically of an Arabidopsis thaliana leaf. Vascular bundles shown.
These plants are called "C3" due to the three-carbon compound (3-Phosphoglyceric acid, or 3-PGA) produced by the CO 2 fixation mechanism in these plants. This C3 mechanism is the first step of the Calvin-Benson cycle, which converts CO 2 and RuBP into 3-PGA.
Plants that do not use PEP-carboxylase in carbon fixation are called C 3 plants because the primary carboxylation reaction, catalyzed by RuBisCO, produces the three-carbon 3-phosphoglyceric acids directly in the Calvin-Benson cycle. Over 90% of plants use C 3 carbon fixation, compared to 3% that use C 4 carbon fixation; [32] however, the ...
C 4 plants have a competitive advantage over plants possessing the more common C 3 carbon fixation pathway under conditions of drought, high temperatures, and nitrogen or CO 2 limitation. When grown in the same environment, at 30 °C, C 3 grasses lose approximately 833 molecules of water per CO 2 molecule that is fixed, whereas C 4 grasses lose ...
A C3 plant uses the Calvin cycle for the initial steps that incorporate CO 2 into organic material. A C4 plant prefaces the Calvin cycle with reactions that incorporate CO 2 into four-carbon compounds. A CAM plant uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. C4 and CAM plants have special adaptations ...
The reverse Krebs cycle, also known as the reverse TCA cycle (rTCA) or reductive citric acid cycle, is an alternative to the standard Calvin-Benson cycle for carbon fixation. It has been found in strict anaerobic or microaerobic bacteria (as Aquificales ) and anaerobic archea .
The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin–Benson cycle, but approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), creating a product that cannot be used within the Calvin–Benson cycle