The citric acid cycle, which can be run in reverse

The reverse Krebs cycle (also known as the reverse tricarboxylic acid cycle, the reverse TCA cycle, or the reverse citric acid cycle) is a sequence of chemical reactions that are used by some bacteria to produce carbon compounds from carbon dioxide and water.

The reaction is basically the citric acid cycle run in reverse. Where the Krebs cycle takes complex carbon molecules in the form of sugars and oxidizes them to CO₂ and water, the reverse cycle takes CO₂ and water to make carbon compounds. This process is used by some bacteria to synthesise carbon compounds, sometimes using hydrogen or sulphates as electron donors.^[1][2] In this process it can be seen as an alternative to the far more common photosynthesis production of organic molecules.

The reaction is a possible candidate for prebiotic early earth conditions and so is of interest in the origin of life research. It has been found that some of the steps can be catalysed by minerals.^[3]

[edit] See also

• Carbon fixation

[edit] References

1. ^ Evans MC; Buchanan BB; Arnon DI (April 1966). "A new ferredoxin-dependent carbon reduction cycle in a photosynthetic bacterium.". Proc Natl Acad Sci U S A. 55 (4): 928–34. doi:10.1073/pnas.55.4.928. PMID 5219700. 
2. ^ Buchanan BB; Arnon DI. (1990). "A reverse KREBS cycle in photosynthesis: consensus at last.". Photosynth Res 24: 47–53. doi:10.1007/BF00032643. PMID 11540925. 
3. ^ Xiang V. Zhang; Scot T. Martin (December 2006). "Driving Parts of Krebs Cycle in Reverse through Mineral Photochemistry". J. Am. Chem. Soc. 128 (50): 16032–16033. doi:10.1021/ja066103k. PMID 17165745. 

[edit] External links

• Prebiotic Soup: Ugly, Yet Simmering with Metabolic Potential

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