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| Organisms that grow by fixing carbon are called autotrophs, which include photoautotrophs (which use sunlight), and lithoautotrophs (which use inorganic oxidation). | | Organisms that grow by fixing carbon are called autotrophs, which include photoautotrophs (which use sunlight), and lithoautotrophs (which use inorganic oxidation). |
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| Seven autotrophic carbon fixation pathways are known.
| | Several autotrophic carbon fixation pathways are known: |
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| '''Calvin cycle''' [https://en.wikipedia.org/wiki/Calvin_cycle] | | '''1) Calvin cycle''' |
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| 3 CO<sub>2</sub> + 6 NADPH + 6 H<sup>+</sup> + 9 ATP + 5 H<sub>2</sub>O → glyceraldehyde-3-phosphate (G3P) + 6 NADP<sup>+</sup> + 9 ADP + 8 P<sub>i</sub> (P<sub>i</sub> = inorganic phosphate) (See also [https://en.wikipedia.org/wiki/Calvin_cycle])
| | [[Calvin cycle]] |
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| ''Step 1'' | | '''2) Reverse Krebs cycle''' |
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| The enzyme [[RuBisCO]] catalyses the carboxylation of <scene name='94/942630/Cv/1'>ribulose-1,5-bisphosphate</scene>, RuBP, a 5-carbon compound, by carbon dioxide (a total of 6 carbons) in a two-step reaction. The product of the first step is enediol-enzyme complex that can capture CO2 or O2. Thus, enediol-enzyme complex is the real carboxylase/oxygenase. The CO2 that is captured by enediol in second step produces an unstable six-carbon compound called 2-carboxy 3-keto 1,5-biphosphoribotol (CKABP) (or 3-keto-2-carboxyarabinitol 1,5-bisphosphate) that immediately splits into 2 molecules of <scene name='39/392339/Cv1/6'>3-phosphoglycerate</scene>, a 3-carbon compound.
| | [[Reverse Krebs cycle]] |
| *[[RuBisCO]]
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| *[[Rubisco and Crop Output]]
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| *[[RuBisCO (Hebrew)]]
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| ''Step 2'' | | '''3) Reductive acetyl CoA pathway''' |
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| The enzyme [[Phosphoglycerate Kinase|phosphoglycerate kinase]] catalyzes the phosphorylation of 3-PGA by ATP (which was produced in the light-dependent stage). <scene name='39/392339/Cv1/5'>1,3-Bisphosphoglycerate</scene> (glycerate-1,3-bisphosphate) and ADP are the products.
| | [[Reductive acetyl CoA pathway]] |
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| ''Step 3'' | | '''4) 3-Hydroxypropionate bicycle''' |
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| The enzyme [[glyceraldehyde-3-phosphate dehydrogenase]] catalyzes the reduction of 1,3BPGA by NADPH (which is another product of the light-dependent stage). Glyceraldehyde 3-phosphate (also called G3P, GP, TP, PGAL, GAP) is produced, and the NADPH itself is oxidized and becomes NADP+. Again, two NADPH are utilized per CO2 fixed.
| | [[3-Hydroxypropionate bicycle]] |
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| </StructureSection> | | </StructureSection> |
| == References == | | == References == |
| <references/> | | <references/> |
