Formose cycle

The Formose Cycle and the Reductive Citric Acid Cycle. 199... 

Are there other types of self-replication in nature, possibly based on a quite different mechanism There are not many, but there is a famous case the formose reaction, described in 1861, and based on a reaction cycle of formaldehyde. This reaction has already been mentioned in Chapter 3, on the subject of prebiotic... 

Figure 7.4 Schemae of the formose reaction (a) spontaneous, slow formation of glycolaldehyde from formaldehyde (b) after one cycle, one new molecule of glycolaldehyde is produced. The structural isomers of sugars are specified by the carbon skeleton and by the position of the carbonyl group (open circle). (Adapted, with some modifications, from Maynard Smith and SzathmSry, 1995.)...

Fig. 12 The formose contains an autocatalytic core, in which the amount of cycle intermediates (such as glycolaldehyde) grows autocatalytically...

One experimental approach would be to generate heterogeneous vesicles in broths containing the constituents of the formose reaction, initially limiting the concentration of formaldehyde. After leaving the system for a while, formaldehyde would be added to the solution. Those vesicles that grew and divided fastest would be selected for. There may be rare conditions under which the constituents of the formose reaction are permeable to the membrane. They enter the vesicle and become trapped as soon as those conditions change. Formaldehyde could then enter the vesicles and allow the autocatalytic cycle to run. 

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