Spontaneous formation and degradation of pool-riffle morphology and sediment sorting using a simple fractional transport model

Understanding the mechanism of spontaneous formation of ribonucleotides under realistic prebiotic conditions is a key open issue of origins-of-life research. In cells, <i>de novo</i> and salvage nucleotide enzymatic synthesis combines 5-phospho-α -D-ribose-1-diphosphate ( α-PRPP) and nucleobases. Interestingly, these reactants are also known as prebiotically plausible compounds. Combining ab initio simulations with mass spectrometry experiments, we compellingly demonstrate that nucleobases and α -PRPP spontaneously combine, through the same facile mechanism, forming both purine and pyrimidine ribonucleotides, under mild hydrothermal conditions. Surprisingly, this mechanism is very similar to the biological one, and yields ribonucleotides with the same anomeric carbon chirality as in biological systems. These results suggest that natural selection might have optimized – through enzymes – a pre-existing ribonucleotide formation mechanism, carrying it forward to modern life forms.

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A common precursor to both prebiotic and biological pathways to RNA nucleotides

10.26434/chemrxiv.5519041.v2 ◽

2017 ◽

Author(s):

Andrea Pérez-Villa ◽

Thomas Georgelin ◽

Jean-François Lambert ◽

Marie-Christine Maurel ◽

François Guyot ◽

...

Keyword(s):

Enzymatic Synthesis ◽

De Novo ◽

Life Forms ◽

Hydrothermal Conditions ◽

Modern Life ◽

Ab Initio Simulations ◽

Spontaneous Formation ◽

Common Precursor ◽

Open Issue ◽

Anomeric Carbon

Understanding the mechanism of spontaneous formation of ribonucleotides under realistic prebiotic conditions is a key open issue of origins-of-life research. In cells, <i>de novo</i> and salvage nucleotide enzymatic synthesis combines 5-phospho-α -D-ribose-1-diphosphate ( α-PRPP) and nucleobases. Interestingly, these reactants are also known as prebiotically plausible compounds. Combining ab initio simulations with mass spectrometry experiments, we compellingly demonstrate that nucleobases and α -PRPP spontaneously combine, through the same facile mechanism, forming both purine and pyrimidine ribonucleotides, under mild hydrothermal conditions. Surprisingly, this mechanism is very similar to the biological one, and yields ribonucleotides with the same anomeric carbon chirality as in biological systems. These results suggest that natural selection might have optimized – through enzymes – a pre-existing ribonucleotide formation mechanism, carrying it forward to modern life forms.

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The Carbon:²³⁴Thorium ratios of sinking particles in the California Current Ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model

10.26434/chemrxiv.7803698 ◽

2019 ◽

Author(s):

Michael Stukel ◽

Thomas Kelly

Keyword(s):

Organic Carbon ◽

Water Column ◽

Particulate Organic Carbon ◽

Transport Model ◽

California Current ◽

In Situ Measurements ◽

Power Law Distribution ◽

Sinking Particles ◽

Organic Carbon Concentration

Thorium-234 (234Th) is a powerful tracer of particle dynamics and the biological pump in the surface ocean; however, variability in carbon:thorium ratios of sinking particles adds substantial uncertainty to estimates of organic carbon export. We coupled a mechanistic thorium sorption and desorption model to a one-dimensional particle sinking model that uses realistic particle settling velocity spectra. The model generates estimates of 238U-234Th disequilibrium, particulate organic carbon concentration, and the C:234Th ratio of sinking particles, which are then compared to in situ measurements from quasi-Lagrangian studies conducted on six cruises in the California Current Ecosystem. Broad patterns observed in in situ measurements, including decreasing C:234Th ratios with depth and a strong correlation between sinking C:234Th and the ratio of vertically-integrated particulate organic carbon (POC) to vertically-integrated total water column 234Th, were accurately recovered by models assuming either a power law distribution of sinking speeds or a double log normal distribution of sinking speeds. Simulations suggested that the observed decrease in C:234Th with depth may be driven by preferential remineralization of carbon by particle-attached microbes. However, an alternate model structure featuring complete consumption and/or disaggregation of particles by mesozooplankton (e.g. no preferential remineralization of carbon) was also able to simulate decreasing C:234Th with depth (although the decrease was weaker), driven by 234Th adsorption onto slowly sinking particles. Model results also suggest that during bloom decays C:234Th ratios of sinking particles should be higher than expected (based on contemporaneous water column POC), because high settling velocities minimize carbon remineralization during sinking.

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