Calvin-Benson-Bassham-cycle

Atmospheric CO2 may be fixed through the Calvin-Benson-Bassham-cycle [13, 23-25]. The key carboxylating enzyme, D-ribulose-l,5-bisphosphate carboxylase/ oxygenase (RubisCO) [26], binds CO2 onto a pentose derivative, ribulose-1,5-bisphosphate. It has been estimated that about 4 x 10 g (40 Mt) of RubisCO exists in the biosphere, which would correspond to an intangible 5 kg of RubisCO per person on Earth [27]. 

However, carbon dioxide is incorporated into the organic substrate and converted into a carboxylate group in the six-carbon sugar derivative. The hydrolysis of the carboxylate (Step 4) affords two molecules of 3-phosphoglycerate, which are incorporated into the gluconeogenesis pathway of glucose synthesis. 

The reductive TCA cycle uses CO2 for producing acetyl-CoA [28, 29]. Two CO2 units are converted in each cycle into acetyl-CoA using one ATP and four NAD(P) H units. The full cycle was first reported to be found in a green sulfur photosynthetic bacterium Chlorobium limicola) and was later also found to operate in Aquificales, Archeal Crenarcheota, and various types of proteobacteria. 

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Calvin-Benson-Bassham cycle (reductive pentose phosphate cycle) 9 6 NAD(P)H RubisCO C02 3 - Phosphogly cerate RubisCO Phosphoribulokinase... 

The NADPH and ATP generated are used within the chloroplast to fix carbon dioxide (CO2) and reduce it to sugar. This sequence of reactions is called the Calvin-Benson-Bassham cycle and this cycle results in the production of the phosphorylated 3-carbon sugar glyceraldehyde-3-phosphate, also called triose. This triose sugar is exported out of the chloroplast and in this course we will refer to it as CH2O which is the chemical composition of sugar when normalized to 1 carbon atom. 

AH the sugar (CH2O) needs to be formed by photosynthesis in the chloroplast. In the Calvin—Benson—Bassham cycle CO2 is reduced to the level of sugar (CH2O) according to the following reaction and stoichiometry ... 

By combining the Calvin—Benson—Bassham cycle with the fight reactions the following general reaction of photosynthesis is then obtained... 

Carbon dioxide (CO2) is processed through the Calvin cycle ([or the Calvin-Benson-Bassham cycle] which is also referred to as the RPP cycle) vide infra. 

Calvin-Benson-Bassham cycle, a seven-carbon sugar arises from the reaction of dihydroxyacetone monophosphate with erythrose 4-phosphate. 

Calvin-Benson-Bassham cycle Production of biomaterials and chemicals from CO Bowien and Kusian (2002)... 

Figure 3.1 The Calvin-Benson-Bassham (CBB) cycle. , phosphoribulokinase , ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO).

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). 

A cycle, by definition, can have no beginning and no end. So, materials are added and withdrawn tangentially as the cycle turns. Many of the features of the Calvin cyde were worked out by Melvin Calvin (Nobel Prize 1961), James Bassham, and Andrew Benson (Harvard University) in the decade immediately following World War II. More information about the Calvin cycle will be presented in Chapter 11. The classic report is Bassham, J. Benson, A. Calvin, M. /. Biol. Chem., 1950,185,781. 

Although some plants, such as those called C4 and those known as using Crassulacean acid metabolism (CAM) photosynthesis (i.e., xerophytes) initially capture the carbon dioxide (CO2) differently than the C3 plants do, they too subsequently release it to the Calvin cycle (M. Calvin [1911-1997], professor. University of California, Berkeley, since 1937, Nobel Prize in Chemistry 1961 Bassham, I Benson, A. Calvin, M. [1950]./ Biol. C/iem., 1950,7S5,781). 

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