94 research outputs found
A thermodynamic basis for prebiotic amino acid synthesis and the nature of the first genetic code
Of the twenty amino acids used in proteins, ten were formed in Miller's
atmospheric discharge experiments. The two other major proposed sources of
prebiotic amino acid synthesis include formation in hydrothermal vents and
delivery to Earth via meteorites. We combine observational and experimental
data of amino acid frequencies formed by these diverse mechanisms and show
that, regardless of the source, these ten early amino acids can be ranked in
order of decreasing abundance in prebiotic contexts. This order can be
predicted by thermodynamics. The relative abundances of the early amino acids
were most likely reflected in the composition of the first proteins at the time
the genetic code originated. The remaining amino acids were incorporated into
proteins after pathways for their biochemical synthesis evolved. This is
consistent with theories of the evolution of the genetic code by stepwise
addition of new amino acids. These are hints that key aspects of early
biochemistry may be universal.Comment: 16 pages, 2 tables, 4 figures. Accepted for publication in
Astrobiolog
Biosignature storage in sulfate minerals- synthetic and natural investigations of the jarosite group minerals
The discovery of jarosite on Mars in 2004 generated increased interest in the properties of the mineral related to the search for life on other planets. Several studies indicate that the formation of jarosite can be linked to biological activity on Earth and biomolecules such as amino acids have been found associated with terrestrial jarosite samples. A series of natural and synthetic investigations using different jarosite end-members has been conducted and is presented in this dissertation to investigate the possibility that jarosite can store biosignatures. Natural samples were analyzed by x-ray diffraction, elemental carbon analysis and laser-desorption Fourier transform mass spectrometry (LD-FTMS) and were found to contain the amino acid glycine. Synthetic experiments were conducted in which the different end-members were synthesized in the presence of glycine as well as the amino acid alanine and the amino acid breakdown product methylamine. These samples were analyzed by x-ray diffraction, neutron diffraction, LD-FTMS and thermogravimetric analysis (TGA) techniques. Results of these experiments show that the detection of the biosignature and the effect that biomolecule has on the jarosite minerals is dependent on the end-member and indicate that the jarosite minerals are an excellent target for detecting potential signs of past life on other planets
A non-energetic mechanism for glycine formation in the interstellar medium
The detection of the amino acid glycine and its amine precursor methylamine on the comet 67P/Churyumov-Gerasimenko by the Rosetta mission provides strong evidence for a cosmic origin of amino acids on Earth. How and when such molecules form along the process of star formation remains debated. Here we report the laboratory detection of glycine formed in the solid phase through atom and radical–radical addition surface reactions under dark interstellar cloud conditions. Our experiments, supported by astrochemical models, suggest that glycine forms without the need for ‘energetic’ irradiation (such as ultraviolet photons and cosmic rays) in interstellar water-rich ices, where it remains preserved, during a much earlier star-formation stage than previously assumed. We also confirm that solid methylamine is an important side-reaction product. A prestellar formation of glycine on ice grains provides the basis for a complex and ubiquitous prebiotic chemistry in space enriching the chemical content of planet-forming material
The Chiral Puzzle of Life
Biological molecules chose one of two structurally, chiral systems which are
related by reflection in a mirror. It is proposed that this choice was made,
causally, by magnetically polarized and physically chiral cosmic-rays, which
are known to have a large role in mutagenesis. It is shown that the cosmic rays
can impose a small, but persistent, chiral bias in the rate at which they
induce structural changes in simple, chiral monomers that are the building
blocks of biopolymers. A much larger effect should be present with helical
biopolymers, in particular, those that may have been the progenitors of RNA and
DNA. It is shown that the interaction can be both electrostatic, just involving
the molecular electric field, and electromagnetic, also involving a magnetic
field. It is argued that this bias can lead to the emergence of a single,
chiral life form over an evolutionary timescale. If this mechanism dominates,
then the handedness of living systems should be universal. Experiments are
proposed to assess the efficacy of this process.Comment: 18 pages, 6 figures, accepted for publication in The Astrophysical
Journal Letters. arXiv admin note: text overlap with arXiv:1911.0252
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