Calvin-Benson cycle carbon

The set of reactions that transforms 3-phosphoglycerate into hexose is named the Calvin-Benson cycle (often referred to simply as the Calvin cycle) for its discoverers. The reaction series is indeed cyclic because not only must carbohydrate appear as an end product, but the 5-carbon acceptor, RuBP, must be regenerated to provide for continual COg fixation. Balanced equations that schematically represent this situation are... 

All the O atoms evolved as Og come from water none comes from carbon dioxide. But 12 O atoms are evolved as 6 Og, and only 6 O atoms appear as 6 HgO in the equation. Also, 6 COg have 12 O atoms, yet there are only 6 O atoms in CgHigOg. How can yon account for these discrepancies Hint Consider the partial reactions of photosynthesis ATP synthesis, NADP reduction, photolysis of water, and the overall reaction for hexose synthesis in the Calvin-Benson cycle.)... 

Purple sulfur bacteria fix carbon dioxide using the Calvin-Benson cycle, but green sulfur bacteria use a completely different pathway, the reverse tricarboxylic acid cycle. Other photosynthetic bacteria use still different pathways for CO2 fixation (Perry and Staley, 1997). 

The light independent reactions take place in the stroma with the help of ATP and NADPH. In a process called the Calvin-Benson cycle, or carbon fixation, carbon dioxide from the atmosphere is captured and converted into carbohydrates [135]. The reaction is catalyzed by the enzyme RuBisCO (ribulose-1,5-biphosphate... 

The overall reaction of carbon dioxide reduction in the Calvin-Benson cycle (Fig. 17-14) becomes... 

This pathway is sometimes called the Calvin-Benson cycle, after the biochemists who elucidated it. The 5-carbon, doubly phosphorylated carbohydrate, ribulose bisphosphate is the acceptor for CO2 the enzyme is called ribulose-bisphosphate carboxylase/oxygenase (called Rubisco). 

Calvin cycle (aka Calvin-Benson Cycle or Carbon Fixation) Series of biochemical, enzyme-mediated reactions during which atmospheric carbon dioxide is reduced and incorporated into organic molecules, eventually some of this forms sugars. In eukaryotes, this occurs in the stroma of the chloroplast. 

PGA (phosphoglycerate) A three-carbon molecule formed when carbon dioxide is added to ribulose biphosphate (RuBP) during the dark reaction of photosynthesis (Calvin, or Calvin-Benson Cycle). PGA is converted to PGAL, using ATP and NADPH. 

The isotopic fingerprinting of photosynthesis. Photosynthesis is currently an important means of fixing inorganic carbon and is used by plants, algae, bacteria, and Archaea. A particularly important enzyme (catalyst) in this process is Rubisco, the official shortened name for a molecule with a much more intricate systematic name. The reactions which take place in this process operate according to the Calvin-Benson Cycle and lead to isotopic fractionations of up to 30%o. 

The lithoautotrophs have to form cellular materials from carbon dioxide. The process to change carbon dioxide into organic compounds is called fixation of carbon dioxide. On the basis of the knowledge to date, all algae and cyanobacteria, and many of the plants, fix carbon dioxide through the Calvin-Benson cycle (or reductive pentose phosphate cycle) (Bassham et al., 1954), while the plants of 20 families and 1200 species have been known to fix carbon dioxide through the Hatch-Slack pathway (or C4 dicarboxylate pathway) (Hatch et al., 1967). 

Plants are divided into two groups for the fixing mechanisms of carbon dioxide plants of one group use the Calvin-Benson cycle, while those of the other group... 

As a result, oxaloacetate (OAA, C4-compound) is formed unlike the case of the Calvin-Benson cycle in which 3-phosphoglycerate (C3-compound) is formed. The pathway in the fixation of carbon dioxide by the catalysis of PEP-carboxylase is observed in sugar cane, corn, etc., and is called the Hatch-Slack pathway (Hatch et al., 1967). The plants having the Hatch-Slack pathway have chloroplasts both in mesophyll cells and in vascular bundle sheath cells, and the Hatch-Slack pathway occurs in the mesophyll cells. Oxaloacetate formed by the fixation of carbon dioxide in the mesophyll cells is reduced to malate. Malate thus formed moves to the vascular bundle sheath cells and releases carbon dioxide there. Carbon dioxide released is fixed by the catalysis of Rubisco, and the organic compounds are formed through the Calvin-Benson cycle. (Fig. 6.3). 

The plants producing organic compounds from carbon dioxide through the Calvin-Benson cycle are called C3-plants, while the plants producing organic compounds from carbon dioxide through the Hatch-Slack pathway are called C4-plants. 

Carbon Dioxide-Fixing Pathways Other than the Calvin-Benson Cycle in the Lithoautotrophs... 

As already mentioned, cyanobacteria and most of the chemolithoautotrophic bacteria fix carbon dioxide through the Calvin-Benson cycle, but some litho-autotrophic bacteria fix carbon dioxide through other pathways. When the green phototrophic bacterium Chloroflexus aurantiacus grows lithoautotrophically, the bacterium fixes carbon dioxide through the 3-hydroxypropionate cycle (Ivanovsky... 

Also common at seeps are the S-oxidising symbionts living in vestimentif-eran tube worms and various clams (Aharon, 2000 Tunnicliffe etal., 2003). These symbionts generally fix C02 by the Calvin-Benson cycle and share some of the carbon they assimilate with their host. 

The NADPH and ATP are used later in the Calvin-Benson Cycle to synthesize carbon hydrates (glucose C6H12O6) via ... 

In the light-independent or dark reactions the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase oxygenase) consumes CO2 from the atmosphere and in a complex process called the Calvin-Benson cycle releases three-carbon sugars that are subsequently combined to form glucose. 

Transketolase (TK) is involved in anaerobic carbohydrate metabolisms such as the nonoxidative phase of the pentose phosphate pathway. In plants and photosynthetic bacteria, TK is involved in the Calvin-Benson cycle. TK catalyses the transfer of a 2-carbon dihydroxyethyl group from a ketose phosphate (donor substrate such as D-xylulose 5-phosphate) to the Cl position of an aldose phosphate (acceptor substrate such as o-ribose 5-phosphate) (Figure 4.3) (Schneider and Lindqvist 1998). The first product is an aldose phosphate released from the donor (such as glyceraldehyde 3-phosphate) and the second is a ketose phosphate (such as sedoheptulose 7-phosphate), in which the 2-carbon fragment is attached to the acceptor. Examples of the substrates and the products mentioned above are for the first reaction of the pentose phosphate pathway. In the second reaction of the same pathway, the acceptor is D-ery-throse 4-phosphate and the second product is o-fructose 6-phosphate. A snapshot X-ray crystallographic study revealed that an ot-carbanion/enamine a,p-dihydroxyethyl ThDP is formed as a key intermediate (Fiedler et al. 2002). Then, a nucleophilic attack of the a-carbanion intermediate on the acceptor substrate occurs. 

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