The plausibility of theories postulating the development of complex chemical organization without …

• Abstract
• Introduction
• Nonenzymatic Metabolism
• The Beilstein Handbook and Citric Acid Cycle
• Conclusions
• Acknowledgements
• References
• Figures

Biology Articles » Evolutionary Biology » Origin of Life » Self-organizing biochemical cycles » Figures

Figures

- Self-organizing biochemical cycles

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Fig. 1.   The reductive (reverse) citric acid cycle adapted from the scheme in Morowitz et al. (13). The nature of the chemical steps is indicated as follows: 1a, introduction of CO₂ and reduction to give an -ketoacid; 1b, introduction of CO₂ to give a -ketoacid; 2a, reduction of a carbonyl group; 2b, reduction of a double bond; 3, reversible hydration/dehydration; and 4, cleavage of citrate to acetate and oxaloacetate.

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Fig. 2.   A simple example of molecular replication in a nonbiological system (17).

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Fig. 3.   The simplest hypothetical autocatalytic formose reaction cycle. In each turn of the cycle, a glycolaldehyde molecule facilitates the synthesis of a second glycolaldehyde molecule from two formaldehyde molecules. The direct formation of glycolaldehyde from formaldehyde does not occur. The stereochemistry of the asymmetric carbon atoms (marked with an asterisk in the diagram) is not specified. The side reaction leading to a branched-chain aldehyde is one of the many reactions that tend to complicate the cycle or divert molecules from it.

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Source: PNAS, vol. 97, no. 23, 12503-12507, November 7, 2000