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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 ...
The overall general equation for the light-independent reactions is the following: [11] 3 CO 2 + 9 ATP + 6 NADPH + 6 H + → C 3 H 6 O 3-phosphate + 9 ADP + 8 P i + 6 NADP + + 3 H 2 O. The 3-carbon products (C 3 H 6 O 3-phosphate) of the Calvin cycle are later converted to glucose or other carbohydrates such as starch, sucrose, and cellulose.
The Calvin cycle (Interactive diagram) The Calvin cycle incorporates carbon dioxide into sugar molecules. The Calvin cycle , also known as the dark reactions , is a series of biochemical reactions that fixes CO 2 into G3P sugar molecules and uses the energy and electrons from the ATP and NADPH made in the light reactions.
Phosphoribulokinase (PRK) (EC 2.7.1.19) is an essential photosynthetic enzyme that catalyzes the ATP-dependent phosphorylation of ribulose 5-phosphate (RuP) into ribulose 1,5-bisphosphate (RuBP), both intermediates in the Calvin Cycle. Its main function is to regenerate RuBP, which is the initial substrate and CO 2-acceptor molecule of the ...
The cyclic light-dependent reactions occur only when the sole photosystem being used is photosystem I. Photosystem I excites electrons which then cycle from the transport protein, ferredoxin (Fd), to the cytochrome complex, b 6 f, to another transport protein, plastocyanin (Pc), and back to photosystem I. A proton gradient is created across the ...
The GP is converted to D-glyceraldehyde 3-phosphate (G3P) using the energy in ATP and the reducing power of NADPH as part of the Calvin cycle. This returns ADP, phosphate ions Pi, and NADP+ to the light-dependent reactions of photosynthesis for their continued function. RuBP is regenerated for the Calvin cycle to continue.
Although this does allow a limited C 4 cycle to operate, it is relatively inefficient. Much leakage of CO 2 from around RuBisCO occurs. There is also evidence of inducible C 4 photosynthesis by non-kranz aquatic macrophyte Hydrilla verticillata under warm conditions, although the mechanism by which CO 2 leakage from around RuBisCO is minimised ...
The Calvin-Benson-Bassham (CBB) cycle is the most common CO 2 fixation pathway found among autotrophs. [16] The key enzyme is ribulose-1,5-bisphosphate carboxylase/oxygenase ( RuBisCO ). [ 15 ] RuBisCO has been identified in members of the microbial community such as Thiomicrospira, Beggiatoa , zetaproteobacterium , and gammaproteobacterial ...