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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 NADPH is then used as a reducing equivalent in the reactions of the Calvin cycle. [2] Electron cycling from ferredoxin to NADPH only occurs in the light in part because FNR activity is inhibited in the dark. [11] In nonphotosynthetic organisms, the FNR primarily works in reverse to provide reduced ferredoxin for various metabolic pathways.
Melvin Calvin and Andrew Benson, along with James Bassham, elucidated the path of carbon assimilation (the photosynthetic carbon reduction cycle) in plants. The carbon reduction cycle is known as the Calvin cycle, but many scientists refer to it as the Calvin-Benson, Benson-Calvin, or even Calvin-Benson-Bassham (or CBB) Cycle.
For example, the oxidation of hydrogen sulfide to elemental sulfur by ½O 2 produces far less energy (50 kcal/mol or 210 kJ/mol) than the oxidation of elemental sulfur to sulfate (150 kcal/mol or 627 kJ/mol) by 3/2 O 2,. [10] The majority of lithotrophs fix carbon dioxide through the Calvin cycle, an energetically expensive process. [6]
This PGA is chemically reduced in the mesophyll and diffuses back to the bundle sheath where it enters the conversion phase of the Calvin cycle. For each CO 2 molecule exported to the bundle sheath the malate shuttle transfers two electrons, and therefore reduces the demand of reducing power in the bundle sheath.
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 .
Nicotinamide adenine dinucleotide phosphate, abbreviated NADP [1] [2] or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NADPH as a reducing agent ('hydrogen source').
Overview of the Calvin cycle and carbon fixation C3 Pathway. 2 H 2 O + 2 NADP + + 3 ADP + 3 P i + light → 2 NADPH + 2 H + + 3 ATP + O 2. The light-independent reactions undergo the Calvin-Benson cycle, in which the energy from NADPH and ATP is used to convert carbon dioxide and water into organic compounds via the enzyme RuBisCO.