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NASA NTRS2004

Workshop on Molecular Evolution

Molecular evolution has become the nexus of many areas of biological research. It both brings together and enriches such areas as biochemistry, molecular biology, microbiology, population genetics, systematics, developmental biology, genomics, bioinformatics, in vitro evolution, and molecular ecology. The Workshop provides an important contribution to these fields in that it promotes interdisciplinary research and interaction, and thus provides a glue that sticks together disparate fields. Due to the wide range of fields addressed by the study of molecular evolution, it is difficult to offer a comprehensive course in a university setting. It is rare for a single institution to maintain expertise in all necessary areas. In contrast, the Workshop is uniquely able to provide necessary breadth and depth by utilizing a large number of faculty with appropriate expertise. Furthermore, the flexible nature of the Workshop allows for rapid adaptation to changes in the dynamic field of molecular evolution. For example, the 2003 Workshop included recently emergent research areas of molecular evolution of development and genomics.

Cummings, Michael P.↗
NASA NTRS1966

Biology and the Exploration of Mars

Until recent years the origin of life and its possible occurrence elsewhere in the universe have been matters for speculation only. The rapid growth of molecular biology since 1940 has, to be sure, made it possible to discuss life's origins in far more precise and explicit terms than was possible earlier; and the subject entered a new experimental phase in the 1950's with successful abiogenic synthesis of important biochemical substances in conditions simulating the presumptive environment of the primitive Earth. But the real transformation that the subject has undergone stems from the spectacular growth of space technology in the last decade. The possibility of life's origin and occurrence on planets other than ours is no longer limited to idle speculation: it has entered the realm of the testable, of science in the strict sense. Given the rockets now available, and especially those available by 1969, it has become fully realistic to consider plans for the biological exploration of Mars. The study that this report seeks to interpret was initiated in June, 1964, by the Space Science Board of the National Academy of Sciences to examine this possibility. The working group comprised 36 people representing a broad spectrum of scientific interests: evolutionary biology, genetics, microbiology, biochemistry and molecular biology, animal physiology, soil chemistry, organic chemistry, planetary astronomy, geochemistry, and theoretical physics. The participants included some with considerable prior involvement in problems of space exploration and others with none. Advice was also sought outside the group of immediate participants on the potentialities of selected analytical methods for the experimental study of extraterrestrial life and its environment. More than 30 individuals contributed in this fashion written assessments of techniques in which they were particularly well versed. Our task was to examine the scientific foundations and merits of the proposal to undertake a biological exploration of Mars. What are the potential scientific yields? How valuable, if attained, would they be? What, in fact, is the possibility of life occurring on Mars? And of our detecting it with available and foreseeable technology? What could be achieved by further astronomical work from Earth? by Martian fly-by missions? by Martian orbiters? and Martian Landers? What payloads would we recommend for planetary missions? What timing and over-all strategy would we recommend for Martian exploration were we to consider it worthwhile at all? In brief, the over-all purpose was to recommend to. the government, through the Academy's Space Science Board, whether or not a biological exploration of Mars should be included in the nation's space program over the next few decades; and, further, to outline what that program, if any, should be.

CONFERENCE↗
NASA NTRSDate not supplied

My Journey to NASA and role as a (Molecular) Biologist…

My journey to NASA started in undergrad, where I performed microbiology research and became hooked in the STEM fields. From there I earned a Ph.D. in Biochemistry and Molecular Biology from Mayo Graduate school where I performed Pancreatic Cancer research and then went on to perform postdoctoral research in Developmental Biology at the University of Miami. Trained as a biologist, I landed my first job at NASA as a mission scientist on the Rodent Research project. As a mission scientist, I led science activities associated with development, flight, and post-flight analysis of rodent research missions on the ISS in consultation with project engineers, operational specialists, mission PI(s), and mission Implementation Partner(s). I also assessed the feasibility of scientific experiments as a technical and scientific expert in rodent research on the ISS. Eager to learn more about the molecular changes that occur as a result of spaceflight exposure, I transitioned to the NASA GeneLab project where I eventually became the data processing lead. NASA’s GeneLab helps scientists understand how the fundamental building blocks of life – DNA, RNA, proteins, and metabolites – change from exposure to the space environment including microgravity and cosmic radiation exposure. GeneLab does so by providing fully coordinated epigenomics, genomics, transcriptomics, proteomics, and metabolomics data (collectively known as omics data) alongside essential metadata describing each spaceflight and space-relevant experiment. To maximize the intelligibility of these data, particularly for users with limited bioinformatics knowledge, GeneLab has started processing and analyzing these datasets to generate differential gene expression data and identify biological and physiological pathways that are dysregulated as a result of spaceflight. The user interface was designed to be accessible to a broad variety of users, including high school and college students who can use it to learn about omics data analysis and space biology. During the CA Space Grant Women in STEM Panel event, I will provide an overview of my journey to NASA including my work at NASA on both the Rodent Research and GeneLab projects. I will conclude by providing resources for opportunities to work with GeneLab and NASA at large followed by links to programs designed specifically to engage women in STEM fields.

Amanda M Saravia-Butler↗
NASA NTRSDate not supplied

My Journey to NASA and Role as a (Molecular) Biologist…

My journey to NASA started in undergrad, where I performed microbiology research and became hooked in the STEM fields. From there I earned a Ph.D. in Biochemistry and Molecular Biology from Mayo Graduate school where I performed Pancreatic Cancer research and then went on to perform postdoctoral research in Developmental Biology at the University of Miami. Trained as a biologist, I landed my first job at NASA as a mission scientist on the Rodent Research project. As a mission scientist, I led science activities associated with development, flight, and post-flight analysis of rodent research missions on the ISS in consultation with project engineers, operational specialists, mission PI(s), and mission Implementation Partner(s). I also assessed the feasibility of scientific experiments as a technical and scientific expert in rodent research on the ISS. Eager to learn more about the molecular changes that occur as a result of spaceflight exposure, I transitioned to the NASA GeneLab project where I eventually became the data processing lead. NASA’s GeneLab helps scientists understand how the fundamental building blocks of life – DNA, RNA, proteins, and metabolites – change from exposure to the space environment including microgravity and cosmic radiation exposure. GeneLab does so by providing fully coordinated epigenomics, genomics, transcriptomics, proteomics, and metabolomics data (collectively known as omics data) alongside essential metadata describing each spaceflight and space-relevant experiment. To maximize the intelligibility of these data, particularly for users with limited bioinformatics knowledge, GeneLab has started processing and analyzing these datasets to generate differential gene expression data and identify biological and physiological pathways that are dysregulated as a result of spaceflight. The user interface was designed to be accessible to a broad variety of users, including high school and college students who can use it to learn about omics data analysis and space biology. During the NASA Ames ECN at Lincoln HS Virtual Panel event, I will provide an overview of my journey to NASA including my work at NASA on both the Rodent Research and GeneLab projects. I will conclude by providing resources for opportunities to work with GeneLab and NASA at large followed by links to programs designed specifically to engage women in STEM fields.

Amanda M Saravia-Butler↗
NASA NTRS2005

The Future of Bio-technology

Hosts of technologies, most notably in electronics, have been on the path of miniaturization for decades and in 2005 they have crossed the threshold of the nano-scale. Crossing the nano-scale threshold is a milestone in miniaturization, setting impressive new standards for component-packing densities. It also brings technology to a scale at which quantum effects and fault tolerance play significant roles and approaches the feasible physical limit form many conventional "top-down" manufacturing methods. I will suggest that the most formidable manufacturing problems in nanotechnology will be overcome and major breakthroughs will occur in a host of technologies, when nanotechnology converges with bio-technology; i.e. I will argue that the future of bio-technology is in nanotechnology. In 2005, methods in molecular biology, microscopy, bioinformatics, biochemistry, and genetic engineering have focused considerable attention on the nano-scale. On this scale, biology is a kind of recursive chemistry in which molecular recognition, self-assembly, self-organization and self-referencing context-control lead to the emergence of the complexity of structures and processes that are fundamental to all life forms. While we are still far from understanding this complexity, we are on the threshold of being able to use at least some of these biological properties for .technology. I will discuss the use of biomolecules, such as DNA, RNA, and proteins as "tools" for the bio-technologist of the future. More specifically, I will present in some detail an example of how we are using a genetically engineered 60-kDa protein (HSP60) from an organism living in near boiling sulfuric acid to build nano-scale templates for arranging metallic nanoparticles. These "extremophile" HSP60s self-assemble into robust double-ring structures called "chaperonins," which further assemble into filaments and arrays with nanometer accuracy. I will discuss our efforts to use chaperonins to organize quantum dots, electronic and magnetic nano-particles for electronic and photonic applications.

Trent, Jonathan↗
NASA NTRS1999

The response of bone to unloading

Skeletal unloading leads to decreased bone formation and decreased bone mass. Bone resorption is uncoupled from bone formation, contributing to the bone loss. During spaceflight bone is lost principally from the bones most loaded in the 1-g environment, and some redistribution of bone from the lower extremities to the head appears to take place. Although changes in calcitropic hormones have been demonstrated during skeletal unloading (PTH and 1,25(OH)2D decrease), it remains unclear whether such changes account for or are in response to the changes in bone formation and resorption. Bed rest studies with human volunteers and hindlimb elevation studies with rats have provided useful data to help explain the changes in bone formation during spaceflight. These models of skeletal unloading reproduce a number of the conditions associated with microgravity, and the findings from such studies confirm many of the observations made during spaceflight. Determining the mechanism(s) by which loading of bone is sensed and translated into a signal(s) controlling bone formation remains the holy grail in this field. Such investigations couple biophysics to biochemistry to cell and molecular biology. Although studies with cell cultures have revealed biochemical responses to mechanical loads comparable to that seen in intact bone, it seems likely that matrix-cell interactions underlie much of the mechanocoupling. The role for systemic hormones such as PTH, GH, and 1,25(OH)2D compared to locally produced factors such as IGF-I, PTHrP, BMPs, and TGF-beta in modulating the cellular response to load remains unclear. As the mechanism(s) by which bone responds to mechanical load with increased bone formation are further elucidated, applications of this knowledge to other etiologies of osteoporosis are likely to develop. Skeletal unloading provides a perturbation in bone mineral homeostasis that can be used to understand the mechanisms by which bone mineral homeostasis is maintained, with the expectation that such understanding will lead to effective treatment for disuse osteoporosis.

NASA Program Fundamental Space Biology↗
NASA NTRS1997

Entropy and charge in molecular evolution--the case of phosphate

Biopoesis, the creation of life, implies molecular evolution from simple components, randomly distributed and in a dilute state, to form highly organized, concentrated systems capable of metabolism, replication and mutation. This chain of events must involve environmental processes that can locally lower entropy in several steps; by specific selection from an indiscriminate mixture, by concentration from dilute solution, and in the case of the mineral-induced processes, by particular effectiveness in ordering and selective reaction, directed toward formation of functional biomolecules. Numerous circumstances provide support for the notion that negatively charged molecules were functionally required and geochemically available for biopoesis. Sulfite ion may have been important in bisulfite complex formation with simple aldehydes, facilitating the initial concentration by sorption of aldehydes in positively charged surface active minerals. Borate ion may have played a similar, albeit less investigated role in forming charged sugar complexes. Among anionic species, oligophosphate ions and charged phosphate esters are likely to have been of even more wide ranging importance, reflected in the continued need for phosphate in a proposed RNA world, and extending its central role to evolved biochemistry. Phosphorylation is shown to result in selective concentration by surface sorption of compounds, otherwise too dilute to support condensation reactions. It provides protection against rapid hydrolysis of sugars and, by selective concentration, induces the oligomerization of aldehydes. As a manifestation of life arisen, phosphate already appears in an organic context in the oldest preserved sedimentary record.

NASA Discipline Exobiology↗
NASA NTRS2003

Tensegrity I. Cell structure and hierarchical systems biology

In 1993, a Commentary in this journal described how a simple mechanical model of cell structure based on tensegrity architecture can help to explain how cell shape, movement and cytoskeletal mechanics are controlled, as well as how cells sense and respond to mechanical forces (J. Cell Sci. 104, 613-627). The cellular tensegrity model can now be revisited and placed in context of new advances in our understanding of cell structure, biological networks and mechanoregulation that have been made over the past decade. Recent work provides strong evidence to support the use of tensegrity by cells, and mathematical formulations of the model predict many aspects of cell behavior. In addition, development of the tensegrity theory and its translation into mathematical terms are beginning to allow us to define the relationship between mechanics and biochemistry at the molecular level and to attack the larger problem of biological complexity. Part I of this two-part article covers the evidence for cellular tensegrity at the molecular level and describes how this building system may provide a structural basis for the hierarchical organization of living systems--from molecule to organism. Part II, which focuses on how these structural networks influence information processing networks, appears in the next issue.

NASA Program Fundamental Space Biology↗
NASA NTRS2011

Development of a Novel Self-Enclosed Sample Preparation Device for DNA/RNA Isolation in Space

Modern biology techniques present potentials for a wide range of molecular, cellular, and biochemistry applications in space, including detection of infectious pathogens and environmental contaminations, monitoring of drug-resistant microbial and dangerous mutations, identification of new phenotypes of microbial and new life species. However, one of the major technological blockades in enabling these technologies in space is a lack of devices for sample preparation in the space environment. To overcome such an obstacle, we constructed a prototype of a DNA/RNA isolation device based on our novel designs documented in the NASA New Technology Reporting System (MSC-24811-1/3-1). This device is self-enclosed and pipette free, purposely designed for use in the absence of gravity. Our design can also be modified easily for preparing samples in space for other applications, such as flowcytometry, immunostaining, cell separation, sample purification and separation according to its size and charges, sample chemical labeling, and sample purification. The prototype of our DNA/RNA isolation device was tested for efficiencies of DNA and RNA isolation from various cell types for PCR analysis. The purity and integrity of purified DNA and RNA were determined as well. Results showed that our developed DNA/RNA isolation device offers similar efficiency and quality in comparison to the samples prepared using the standard protocol in the laboratory.

Zhang, Ye↗
NASA NTRS2000

The origin of cellular life

This essay presents a scenario of the origin of life that is based on analysis of biological architecture and mechanical design at the microstructural level. My thesis is that the same architectural and energetic constraints that shape cells today also guided the evolution of the first cells and that the molecular scaffolds that support solid-phase biochemistry in modern cells represent living microfossils of past life forms. This concept emerged from the discovery that cells mechanically stabilize themselves using tensegrity architecture and that these same building rules guide hierarchical self-assembly at all size scales (Sci. Amer 278:48-57;1998). When combined with other fundamental design principles (e.g., energy minimization, topological constraints, structural hierarchies, autocatalytic sets, solid-state biochemistry), tensegrity provides a physical basis to explain how atomic and molecular elements progressively self-assembled to create hierarchical structures with increasingly complex functions, including living cells that can self-reproduce.

Review, Academic↗
NASA NTRS2007

Anti-radiation vaccine: Immunologically-based Prophylaxis of Acute Toxic Radiation Syndromes Associated with Long-term Space Flight

Protecting crew from ionizing radiation is a key life sciences problem for long-duration space missions. The three major sources/types of radiation are found in space: galactic cosmic rays, trapped Van Allen belt radiation, and solar particle events. All present varying degrees of hazard to crews; however, exposure to high doses of any of these types of radiation ultimately induce both acute and long-term biological effects. High doses of space radiation can lead to the development of toxicity associated with the acute radiation syndrome (ARS) which could have significant mission impact, and even render the crew incapable of performing flight duties. The creation of efficient radiation protection technologies is considered an important target in space radiobiology, immunology, biochemistry and pharmacology. Two major mechanisms of cellular, organelle, and molecular destruction as a result of radiation exposure have been identified: 1) damage induced directly by incident radiation on the macromolecules they encounter and 2) radiolysis of water and generation of secondary free radicals and reactive oxygen species (ROS), which induce chemical bond breakage, molecular substitutions, and damage to biological molecules and membranes. Free-radical scavengers and antioxidants, which neutralize the damaging activities of ROS, are effective in reducing the impact of small to moderate doses of radiation. In the case of high doses of radiation, antioxidants alone may be inadequate as a radioprotective therapy. However, it remains a valuable component of a more holistic strategy of prophylaxis and therapy. High doses of radiation directly damage biological molecules and modify chemical bond, resulting in the main pathological processes that drive the development of acute radiation syndromes (ARS). Which of two types of radiation-induced cellular lethality that ultimately develops, apoptosis or necrosis, depends on the spectrum of incident radiation, dose, dose rate, and functional conditions of impacted cells/organisms. The administration of an experimental anti-radiation vaccine may provide an immunologically based, adjunct method of prevention or prophylaxis against clinical ARS. The administration of experimental anti-radiation serum (ARS) and the use of the blood dialysis methods, such as immune plasma-sorption, may assist in the clearance of radiation-specific toxins and may enhance established strategies for the mitigation of the biological effects leading to ARS, and should be evaluated for use on exploration-class space missions.

Popov, Dmitri↗
NASA NTRS1993

Evolution in vitro: analysis of a lineage of ribozymes

Background: Catalytic RNAs, or ribozymes, possessing both a genotype and a phenotype, are ideal molecules for evolution experiments in vitro. A large, heterogeneous pool of RNAs can be subjected to multiple rounds of selection, amplification and mutation, leading to the development of variants that have some desired phenotype. Such experiments allow the investigator to correlate specific genetic changes with quantifiable alterations of the catalytic properties of the RNA. In addition, patterns of evolutionary change can be discerned through a detailed examination of the genotypic composition of the evolving RNA population. Results: Beginning with a pool of 10(13) variants of the Tetrahymena ribozyme, we carried out in vitro evolution experiments that led to the generation of ribozymes with the ability to cleave an RNA substrate in the presence of Ca2+ ions, an activity that does not exist for the wild-type molecule. Over the course of 12 generations, a seven-error variant emerged that has substantial Ca(2+)-dependent RNA-cleavage activity. Advantageous mutations increased in frequency in the population according to three distinct dynamics--logarithmic, linear and transient. Through a comparative analysis of 31 individual variants, we infer how certain mutations influence the catalytic properties of the ribozyme. Conclusions: In vitro evolution experiments make it possible to elucidate important aspects of both evolutionary biology and structural biochemistry on a reasonable short time scale.

Non-NASA Center↗
NASA NTRS1971

Chemical evolution and the origin of life; Proceedings of the Third International Conference, Pont-a-Mousson, France, April 19-25, 1970. Volume 1 - Molecular evolution.

The present state of investigations on the origin of life is surveyed together with the current state of molecular paleontology. General and theoretical subjects discussed include an energetic approach to prebiological chemistry, the recognition of description and function in chemical reaction networks, and the origin and development of optical activity of bio-organic compounds on the primordial earth. Other fields considered are the syntheses of small molecules, oligomers and polymers; photochemical processes; the origin of biological structures; primitive biochemistry and biology; and exobiology. Individual items are abstracted in this issue.

Buvet, R.↗
NASA NTRS1998

In search of cellular control: signal transduction in context

The field of molecular cell biology has experienced enormous advances over the last century by reducing the complexity of living cells into simpler molecular components and binding interactions that are amenable to rigorous biochemical analysis. However, as our tools become more powerful, there is a tendency to define mechanisms by what we can measure. The field is currently dominated by efforts to identify the key molecules and sequences that mediate the function of critical receptors, signal transducers, and molecular switches. Unfortunately, these conventional experimental approaches ignore the importance of supramolecular control mechanisms that play a critical role in cellular regulation. Thus, the significance of individual molecular constituents cannot be fully understood when studied in isolation because their function may vary depending on their context within the structural complexity of the living cell. These higher-order regulatory mechanisms are based on the cell's use of a form of solid-state biochemistry in which molecular components that mediate biochemical processing and signal transduction are immobilized on insoluble cytoskeletal scaffolds in the cytoplasm and nucleus. Key to the understanding of this form of cellular regulation is the realization that chemistry is structure and hence, recognition of the the importance of architecture and mechanics for signal integration and biochemical control. Recent work that has unified chemical and mechanical signaling pathways provides a glimpse of how this form of higher-order cellular control may function and where paths may lie in the future.

Non-NASA Center↗
NASA NTRS1994

Use of Molecular Fossils for the Interpretation of Paleoenvironments on Early Earth: The Synthesis of Lipid Biomarkers by Methane-Oxidizing Bacteria

Over the course of Earth's history, the most important biological influence has come from the evolution of oxygenic photosynthesis and the development of an oxygen-rich biosphere. Although the availability of free oxygen had profound effects on subsequent biological and planetary evolution, clear paleobiological evidence of the timing of this transition is lacking. Recent technical advances in the microanalysis of organic matter has made it possible to detect residual molecules (biomarkers) in proterozoic (2.5 to 0.6 billion years) sedimentary rock characteristic of specific groups of microorganisms. When coupled with the carbon isotopic fractionations characteristic of biological systems and the new field of compound specific isotope analysis, biomarkers could prove to be a powerful tool for decoding ancient biochemistry from the geological record. We have been studying the carbon isotope fractionations associated with the synthesis of organic biomarker molecules in several types of methane-oxidizing bacteria that should have been key to carbon cycling in paleoenvironments after the evolution of oxygenic photosynthesis.

Jahnke, Linda L.↗
NASA NTRS2014

Cofactors in the RNA World

RNA world theories figure prominently in many scenarios for the origin and early evolution of life. These theories posit that RNA molecules played a much larger role in ancient biology than they do now, acting both as the dominant biocatalysts and as the repository of genetic information. Many features of modern RNA biology are potential examples of molecular fossils from an RNA world, such as the pervasive involvement of nucleotides in coenzymes, the existence of natural aptamers that bind these coenzymes, the existence of natural ribozymes, a biosynthetic pathway in which deoxynucleotides are produced from ribonucleotides, and the central role of ribosomal RNA in protein synthesis in the peptidyl transferase center of the ribosome. Here, we uses both a top-down approach that evaluates RNA function in modern biology and a bottom-up approach that examines the capacities of RNA independent of modern biology. These complementary approaches exploit multiple in vitro evolution techniques coupled with high-throughput sequencing and bioinformatics analysis. Together these complementary approaches advance our understanding of the most primitive organisms, their early evolution, and their eventual transition to modern biochemistry.

RNA↗
NASA NTRS1999

How cells (might) sense microgravity

This article is a summary of a lecture presented at an ESA/NASA Workshop on Cell and Molecular Biology Research in Space that convened in Leuven, Belgium, in June 1998. Recent studies are reviewed which suggest that cells may sense mechanical stresses, including those due to gravity, through changes in the balance of forces that are transmitted across transmembrane adhesion receptors that link the cytoskeleton to the extracellular matrix and to other cells (e.g., integrins, cadherins, selectins). The mechanism by which these mechanical signals are transduced and converted into a biochemical response appears to be based, in part, on the finding that living cells use a tension-dependent form of architecture, known as tensegrity, to organize and stabilize their cytoskeleton. Because of tensegrity, the cellular response to stress differs depending on the level of pre-stress (pre-existing tension) in the cytoskeleton and it involves all three cytoskeletal filament systems as well as nuclear scaffolds. Recent studies confirm that alterations in the cellular force balance can influence intracellular biochemistry within focal adhesion complexes that form at the site of integrin binding as well as gene expression in the nucleus. These results suggest that gravity sensation may not result from direct activation of any single gravioreceptor molecule. Instead, gravitational forces may be experienced by individual cells in the living organism as a result of stress-dependent changes in cell, tissue, or organ structure that, in turn, alter extracellular matrix mechanics, cell shape, cytoskeletal organization, or internal pre-stress in the cell-tissue matrix.--Ingber, D. How cells (might) sense microgravity.

NASA Discipline Cell Biology↗
NASA NTRS2011

Distinct Purine Distribution in Carbonaceous Chondrites

Carbonaceous chondrite meteorites are known to contain a diverse suite of organic compounds, many of which are essential components of biochemistry. Amino acids, which are the monomers of proteins, have been extensively studied in such meteorites (e.g. Botta and Bada 2002; Pizzarello et aI., 2006). The origin of amino acids in meteorites has been firmly established as extraterrestrial based on their detection typically as racemic mixtures of amino acids, the presence of many non-protein amino acids, and non-terrestrial values for compound-specific deuterium, carbon, and nitrogen isotopic measurements. In contrast to amino acids, nucleobases in meteorites have been far less studied. Nucleobases are substituted one-ring (pyrimidine) or two-ring (purine) nitrogen heterocyclic compounds and serve as the information carriers of nucleic acids and in numerous coenzymes. All of the purines (adenine, guanine, hypoxanthine, and xanthine) and pyrimidines (uracil) previously reported in meteorites are biologically common and could be interpreted as the result of terrestrial contamination (e.g. van del' Velden and Schwartz, 1974.) Unlike other meteoritic organics, there have been no observations of stochastic molecular diversity of purines and pyrimidines in meteorites, which has been a criterion for establishing extraterrestrial origin. Maltins et al. (2008) performed compound-specific stable carbon isotope measurements for uracil and xanthine in the Murchison meteorite. They assigned a non-terrestrial origin for these nucleobases; however, the possibility that interfering indigenous molecules (e.g. carboxylic acids) contributed to the 13C-enriched isotope values for these nucleobases cannot be completely ruled out. Thus, the origin of these meteoritic nucleobases has never been established unequivocally. Here we report on our investigation of extracts of II different carbonaceous chondrites covering various petrographic types (Cl, CM, and CR) and degrees of aqueous alteration (l, 2, and 3) and one ureilite. Analysis via liquid chromatography coupled with electrospray triple-stage mass spectrometry or orbitrap mass spectrometry employed a targeted approach for analysis focused on the five canonical RNA/DNA nucleobases as well as 14 non-canonical pyrimidines and purines, which have bcen observed under plausible prebiotic reactions.

Callahan, Michael P.↗