Possible Ribose Synthesis in Carbonaceous Planetesimals

Abstract

The origin of life might be sparked by the polymerization of the first RNA molecules in Darwinian ponds during wet-dry cycles. The key life-building block ribose was found in carbonaceous chondrites. Its exogenous delivery onto the Hadean Earth could be a crucial step toward the emergence of the RNA world. Here, we investigate the formation of ribose through a simplified version of the formose reaction inside carbonaceous chondrite parent bodies. Following up on our previous studies regarding nucleobases with the same coupled physico-chemical model, we calculate the abundance of ribose within planetesimals of different sizes and heating histories. We perform laboratory experiments using catalysts present in carbonaceous chondrites to infer the yield of ribose among all pentoses (5Cs) forming during the formose reaction. These laboratory yields are used to tune our theoretical model that can only predict the total abundance of 5Cs. We found that the calculated abundances of ribose were similar to the ones measured in carbonaceous chondrites. We discuss the possibilities of chemical decomposition and preservation of ribose and derived constraints on time and location in planetesimals. In conclusion, the aqueous formose reaction might produce most of the ribose in carbonaceous chondrites. Together with our previous studies on nucleobases, we found that life-building blocks of the RNA world could be synthesized inside parent bodies and later delivered onto the early Earth.

Prebiotic Vitamin B3 Synthesis in Carbonaceous Planetesimals

“…We tested the thermodynamic favorability of our newly proposed reaction (see Scheme 1) and evaluated the resulting abundances in comparison to measurements in carbonaceous chondrites and asteroids. We conclude that it fits well into the complex network of other prebiotic pathways, e. g., Strecker, [55,69] Fischer-Tropsch, [42,44,46,122] or formose [45] reactions active in the aqueous phase of planetesimals. More detailed modeling of competition between these pathways is needed, e. g., the interplay with the formose reaction.…”

“…The other necessary building blocks for NAD have also been found in meteorites, [40][41][42][43] and their synthesis mechanisms have already been explored in the aqueous environment of the interior of meteorite parent bodies. [44][45][46] The nucleobase adenine was found in carbonaceous chondrites [40][41][42] and its synthesis has been explained by previous models that agree with the measured values. [44,46] The same is true for ribose, which was also found in carbonaceous chondrites, [43] and its synthesis was investigated in a previous study.…”

“…[55,80,81] The sugar precursors glyceraldehyde and dihydroxyacetone are easily formed via the formose reaction, which was shown to successfully describe the synthesis of ribose inside carbonaceous planetesimals. [45] Other necessary reactants, formaldehyde and glycolaldehyde, are also available (see Table 1). The formose reaction requires catalysts providing an alkaline environment, e. g., hydroxides or carbonates, [82] which have also been found in carbonaceous chondrites.…”

“…[44,46] The same is true for ribose, which was also found in carbonaceous chondrites, [43] and its synthesis was investigated in a previous study. [45] Furthermore, the mineral schreibersite, which is capable of providing phosphate groups and phosphorylating nucleosides, [47] is present in enstatite iron meteorites. [48][49][50] This makes nicotinamide the only piece needed for a complete building kit of NAD that could have been delivered to the early Earth by meteorites.…”

Meteorites and the RNA World: Synthesis of Nucleobases in Carbonaceous Planetesimals and the Role of Initial Volatile Content

“…This molecule offers another excellent chance to model its formation in the parent bodies of the carbonaceous chondrites. In a follow-up study, we modeled its synthesis with our model, starting from formaldehyde and glycolaldehyde as reactants (Paschek et al 2022). Thermodynamic data and initial concentrations for glycolaldehyde are available from the previous study by Cobb et al (2015).…”