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The Calvin cycle, light-independent reactions, bio synthetic phase, dark reactions, or photosynthetic carbon reduction (PCR) cycle [1] of photosynthesis is a series of chemical reactions that convert carbon dioxide and hydrogen-carrier compounds into glucose. The Calvin cycle is present in all photosynthetic eukaryotes and also many ...
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. Drawing based on microscopic images ...
This ability to avoid photorespiration makes these plants more hardy than other plants in dry and hot environments, wherein stomata are closed and internal carbon dioxide levels are low. Under these conditions, photorespiration does occur in C 4 plants, but at a much lower level compared with C 3 plants in the same conditions.
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 ...
C3 plants use the Calvin cycle to fix carbon. C4 plants use a modified Calvin cycle in which they separate Ribulose-1,5-bisphosphate carboxylase oxygenase (RuBisCO) from atmospheric oxygen, fixing carbon in their mesophyll cells and using oxaloacetate and malate to ferry the fixed carbon to RuBisCO and the rest of the Calvin cycle enzymes ...
The concentration of NADPH in the chloroplast may help regulate which pathway electrons take through the light reactions. When the chloroplast runs low on ATP for the Calvin cycle, NADPH will accumulate and the plant may shift from noncyclic to cyclic electron flow.
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 .
RpiA plays an essential role in the metabolism of plants and animals, as it is involved in the Calvin cycle which takes place in plants, and the pentose phosphate pathway which takes place in plants as well as animals. All orthologs of the enzyme maintain an asymmetric tetramer quaternary structure with a cleft containing the active site. Each ...