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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.
In the light-independent (or "dark") reactions, the enzyme RuBisCO captures CO 2 from the atmosphere and, in a process called the Calvin cycle, uses the newly formed NADPH and releases three-carbon sugars, which are later combined to form sucrose and starch. The overall equation for the light-independent reactions in green plants is [27]: 128
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 .
RuBisCO is important biologically because it catalyzes the primary chemical reaction by which inorganic carbon enters the biosphere.While many autotrophic bacteria and archaea fix carbon via the reductive acetyl CoA pathway, the 3-hydroxypropionate cycle, or the reverse Krebs cycle, these pathways are relatively small contributors to global carbon fixation compared to that catalyzed by RuBisCO.
The series of biochemical redox reactions which take place in the stroma are collectively called the Calvin cycle or light-independent reactions. There are three phases: carbon fixation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.
Melvin Ellis Calvin (April 8, 1911 – January 8, 1997) [3] was an American biochemist known for discovering the Calvin cycle along with Andrew Benson and James Bassham, for which he was awarded the 1961 Nobel Prize in Chemistry. He spent most of his five-decade career at the University of California, Berkeley.
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 ...