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All sourcesNASA NTRSDOE OSTI
NASA NTRS2019

Quantifying the Evolution of Molecular Production Rates of Comet 21P/Giacobini–Zinner with iSHELL/NASA-IRTF

This paper presents results from our molecular characterization of comet 21P/Giacobini–Zinner during its 2018 apparition. We followed the comet during four observing runs, for a total of eight nights. The high-resolution spectra of 21P were acquired using iSHELL—the near-infrared high-resolution immersion echelle spectrograph on NASA/IRTF (Maunakea, Hawaii). We detected many cometary emission lines across four customized iSHELL settings in the (2.9–5.2) μm range. CO abundances relative to water displayed a relatively constant behavior during the observing campaign, suggesting a possible correlation between the outgassing of water and CO. While CO mixing ratios in 21P are consistent with the reference median value for Jupiter family comets (JFCs), ethane was depleted relative to the reference median value for JFCs, except for one observing run (August 8 and 9) in which ethane appeared overabundant. We consider several possible causes: an ethane outburst, decreasing outgassing of water, or a seasonal effect owing to nucleus rotation. In the pre-perihelion runs, methanol was overabundant compared with the reference median value for JFCs, however it decreased steadily to a depleted value during 21P’s post-perihelion phase, suggesting a possible seasonal effect. We report 3σ upper limits for acetylene, formaldehyde, ammonia, and methane. The ratios of our measured 3σ upper limits for acetylene and detections of hydrogen cyanide are consistent with the depletion of C2 relative to CN in 21P observed at optical wavelengths. This result confirms that 21P is depleted in the carbon-chain primary volatile responsible for C2.

Faggi, S.↗
NASA NTRS2019

Quantifying the Evolution of Molecular Production Rates of Comet 21P/Giacobini–Zinner with iSHELL/NASA-IRTF

This paper presents results from our molecular characterization of comet 21P/Giacobini-Zinner during its 2018 apparition. We followed the comet during four observing runs, for a total of 8 nights. The high-resolution spectra of 21P were acquired using iSHELL - the near-IR high resolution immersion echelle spectrograph on NASA/IRTF (Mauna Kea, Hawaii). We detected many cometary emission lines across four customized iSHELL settings in the (2.9 – 5.2) μm range. CO abundances relative to water displayed a relatively constant behavior during the observing campaign, suggesting a possible correlation between the outgassing of water and CO. While CO mixing ratios in 21P are consistent with the reference median value for Jupiter Family comets (JFCs), ethane was depleted relative to the reference median value for JFCs, excepting one observing run (8th and 9th Aug) in which ethane appeared overabundant. We consider several possible causes: an ethane outburst, decreasing outgassing of water, or a seasonal effect owing to nucleus rotation. In the pre-perihelion runs, methanol was overabundant compared with the reference median value for JFCs, however it decreased steadily to a depleted value during 21P’s post-perihelion phase, suggesting a possible seasonal effect. We report 3-s upper limits for acetylene, formaldehyde, ammonia and methane. The ratios of our measured 3-s upper limits for acetylene and detections of hydrogen cyanide are consistent with the depletion of C2 relative to CN in 21P observed at optical wavelengths. This result confirms that 21P is depleted in the carbon chain primary volatile responsible for C2 production.

Faggi S.↗
NASA NTRS1991

On the origin and early evolution of biological catalysis and other studies on chemical evolution

One of the lines of research in molecular evolution which we have developed for the past three years is related to the experimental and theoretical study of the origin and early evolution of biological catalysis. In an attempt to understand the nature of the first peptidic catalysts and coenzymes, we have achieved the non-enzymatic synthesis of the coenzymes ADPG, GDPG, and CDP-ethanolamine, under conditions considered to have been prevalent on the primitive Earth. We have also accomplished the prebiotic synthesis of histidine, as well as histidyl-histidine, and we have measured the enhancing effects of this catalytic dipeptide on the dephosphorylation of deoxyribonucleotide monophosphates, the hydrolysis of oligo A, and the oligomerization 2', 3' cAMP. We reviewed and further developed the hypothesis that RNA preceded double stranded DNA molecules as a reservoir of cellular genetic information. This led us to undertake the study of extant RNA polymerases in an attempt to discover vestigial sequences preserved from early Archean times. In addition, we continued our studies of on the chemical evolution of organic compounds in the solar system and beyond.

Oro, J.↗
NASA NTRS1999

The influence of UV radiation on protistan evolution

Ultraviolet radiation has provided an evolutionary challenge to life on Earth. Recent increases in surficial ultraviolet B fluxes have focused attention on the role of UV radiation in protistan ecology, cancer, and DNA damage. Exploiting this new wealth of data, I examine the possibility that ultraviolet radiation may have played a significant role in the evolution of the first eukaryotes, that is, protists. Protists probably arose well before the formation of a significant ozone shield, and thus were probably subjected to substantial ultraviolet A, ultraviolet B, and ultraviolet C fluxes early in their evolution. Evolution consists of the generation of heritable variations and the subsequent selection of these variants. Ultraviolet radiation has played a role both as a mutagen and as a selective agent. In its role as a mutagen, it may have been crucial in the origin of sex and as a driver of molecular evolution. As a selective agent, its influence has been broad. Discussed in this paper are the influence of ultraviolet radiation on biogeography, photosynthesis, and desiccation resistance.

NASA Center ARC↗
NASA NTRS1999

A molecular description of the evolution of resistance

BACKGROUND: In vitro evolution has been used to obtain nucleic acid molecules with interesting functional properties. The evolution process usually is carried out in a stepwise manner, involving successive rounds of selection, amplification and mutation. Recently, a continuous in vitro evolution system was devised for RNAs that catalyze the ligation of oligonucleotide substrates, allowing the evolution of catalytic function to be studied in real time. RESULTS: Continuous in vitro evolution of an RNA ligase ribozyme was carried out in the presence of a DNA enzyme that was capable of cleaving, and thereby inactivating, the ribozyme. The DNA concentration was increased steadily over 33.5 hours of evolution, reaching a final concentration that would have been sufficient to inactivate the starting population in one second. The evolved population of ribozymes developed resistance to the DNA enzyme, reducing their vulnerability to cleavage by 2000-fold but retaining their own catalytic function. Based on sequencing and kinetic analysis of the ribozymes, two mechanisms are proposed for this resistance. One involves three nucleotide substitutions, together with two compensatory mutations, that alter the site at which the DNA enzyme binds the ribozyme. The other involves enhancement of the ribozyme's ability to bind its own substrate in a way that protects it from cleavage by the DNA enzyme. CONCLUSIONS: The ability to direct the evolution of an enzyme's biochemical properties in response to the behavior of another macromolecule provides insight into the evolution of resistance and may be useful in developing enzymes with novel or enhanced function.

Non-NASA Center↗
NASA NTRS1998

Of mice and genes: evolution of vertebrate brain development

In this review the current understanding of genetic and molecular evolution of development, in particular the formation of the major axis of bilateral animals, is critically evaluated, and the early pattern formation in the hindbrain is related as much as possible to these processes. On the genetic level it is proposed that the exuberant multiplication of regulatory genes compared to that of structural genes relates to the increased flexibility of early vertebrate development. In comparisons to fruit flies, many conserved genes are found to be expressed very differently, while many others seem to reflect a comparable pattern and thus suggest a conservation of function. Even genes with a largely conserved pattern of expression may change the level at which they are expressed and the mechanisms by which they are regulated in their expression. Evolution and development of hindbrain motoneurons is reviewed, and it is concluded that both comparative data as well as more recent experimental data suggest a limited importance for the rhombomeres. Clearly, many cell fate-specifying processes work below the level of rhombomeres or in the absence of rhombomeres. It is suggested that more comparative developmental data are needed to establish firmly the relationship between homeobox genes and rhombomere specification in vertebrates other than a few model species.

NASA Discipline Developmental Biology↗
NASA NTRS1993

The RNA-world and co-evolution hypothesis and the origin of life: Implications, research strategies and perspectives

The applicability of the RNA-world and co-evolution hypothesis to the study of the very first stages of the origin of life is discussed. The discussion focuses on the basic differences between the two hypotheses and their implications, with regard to the reconstruction methodology, ribosome emergence, balance between ribozymes and protein enzymes, and their major difficultites. Additional complexities of the two hypotheses, such as membranes and the energy source of the first reactions, are not treated in the present work. A central element in the proposed experimental strategies is the study of the catalytic activites of very small peptides and RNA-like oligomers, according to existing, as well as to yet-to-be-invented scenarios of the two hypothesis under consideration. It is suggested that the novel directed molecular evolution technology, and molecular computational modeling, can be applied to this research. This strategy is assumed to be essential for the suggested goal of future studies of the origin of life, namely, the establishment of a `Primordial Darwinian entity'.

Lahav, Noam↗
NASA NTRS1985

The synthesis of primitive 'living' forms - Definitions, goals, strategies and evolution synthesizers

The arbitrariness of the definition of life is discussed in relation to both the archaic biological entities that preceded cells during the Molecular Evolution era, and the hypothetical, primitive, 'living' entities that presumably can be synthesized in the laboratory. Several experimental approaches to the synthesis, detection, and characterization of 'living' entities are discussed. The experimental approaches considered for the synthesis are the constructionist strategy, the whole-environment strategy, and the modular strategy, which is a combination of the first two. The whole-environment strategy is discussed in more detail and the establishment of an Evolution Synthesizer, based on this strategy, is proposed and rationalized. The guidelines for the detection and characterization of populations and processes of 'living' entities include chemical and physical analyses, but are based mainly on the reproductive characterization of these entities. It is expected that the higher the evolutionary level of the 'living' entities, the longer and more difficult it will be to synthesize them, but the easier it will be to detect them.

Lahav, N.↗
NASA NTRS1994

Double layer hydroxide minerals as host structures for bioorganic molecules

A central problem in molecular evolution concerns the selective concentration from dilute, multicomponent solution of source molecules into a reactive environment, where formation of larger molecular assemblages can take place. Minerals consisting of positively charged, separable metal hydroxide sheets have proven capable of these functions. This common structural type is represented by minerals such as pyroaurite (Mg-Fe(3+) hydroxide), hydrotalcite (Mg-Al), green rust Fe(2+)-Fe(3+) and others. Effective interlayer sorption is demonstrated for orthophosphate and condensed phosphates, anionic alkyl compounds, polypeptides, nucleic acids, cyanide complexes and glycolaldehyde phosphate, the latter shown to readily oligomerize to form and selectively retain racemic hexose -2, 4, 6-phosphates, preferentially of altrose (Pitsch, et al, 1993). The selective aldomerization and retention effects correlate with the charge distribution in the host mineral structure and the stereochemistry of the substrate molecules. Interaction between nucleic acid bases, and between the cyanide groups of glycolaldehyde phosphate nitrile at the low water activity in the mineral interlayer is indicated by doubling of the monomeric separation of the hydroxide mineral sheets.

Lee, Ton↗
NASA NTRS1974

The prebiotic synthesis of oligonucleotides

This paper is primarily a review of recent developments in the abiotic synthesis of nucleotides, short chain oligonucleotides, and their mode of replication in solution. It also presents preliminary results from this laboratory on the prebiotic synthesis of thymidine oligodeoxynucleotides. A discussion, based on the physicochemical properties of RNA and DNA oligomers, relevant to the molecular evolution of these compounds leads to the tentative hypothesis that oligodeoxyribonucleotides of about 12 units may have been of sufficient length to initiate a self replicating coding system. Two models are suggested to account for the synthesis of high molecular weight oligomers using short chain templates and primers.

Oro, J.↗
NASA NTRS1997

Mineral induced phosphorylation of glycolate ion--a metaphor in chemical evolution

Bilateral surface-active minerals with excess positive charge concentrate glycolate and trimetaphosphate ion from l0(-3) m aqueous solution to half-saturation of the internal surface sites, and induce phosphorylation of glycolate ion in the mineral with trimetaphosphate, sorbed from l0(-2) m solution. By utilizing reactants from dilute solution at near-neutral pH, and eliminating the need for participating organic nitrogen compounds, the reaction comprises several elements considered necessary for geochemical realism in models for molecular evolution.

NASA Discipline Exobiology↗
NASA NTRS1977

Chemical Evolution and the Origin of Life: Bibliography 1975

This bibliography is the sixth annual supplement to the comprehensive bibliography on the same subject which was published in Space Life Sci.We would like to draw attention to a recently published cumulative bibliography on this same subject: Biochemical Origin of Life: Chemistry and Life. Soil and Water and Its Relationship to Origin of Life. MR - Studies of Prebiotic Polypeptides. Energy, Matter, and Life. Prospects for the Future Orientation of Scientific Research. Photochemical Formation of Self Sustaining Coacervates. Photochemical Formation of Self-Sustaining Coacervates. Comparative Study of Abiogenesis of Cysteine and Other Amino Acids Catalyzed by Various Metal Ions. Protein Structure and the Molecular Evolution of Biological Energy Conversion. Origin of Life. Clues from Relations Between Chemical Compositions of Living Organisms and Natural Environments. Shock Synthesis of Amino Acids II.', Origins of Life 6(1-2). Dynamics of the Chemical Evolution of Earth's Primitive Atmosphere. The Mechanisms of Amino Acids Synthesis by High Temperature Shock-Waves. Theory of Chemical Evolution. Physical Foundations of Probability of Biogenesis.

West, Martha W.↗
NASA NTRS1999

Efficient transfer of information from hexitol nucleic acids to RNA during nonenzymatic oligomerization

Hexitol nucleic acids (HNAs) are DNA analogues that contain the standard nucleoside bases attached to a phosphorylated 1,5-anhydrohexitol backbone. We find that HNAs support efficient information transfer in nonensymatic template-directed reactions. HNA heterosequences appeared to be superior to the corresponding DNA heterosequences in facilitating synthesis of complementary oligonucleotides from nucleoside-5'-phosphoro-2-methyl imidazolides.

Non-NASA Center↗