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During 20 years, the European astrobiologists collaborated within EANA, the European Astrobiology Network Association, to help European researchers developing astrobiology programmes to share their knowledge, to foster their cooperation, to attract young scientists to this quickly evolving interactive field of research, and to explain astrobiology to the public at large. The experiment of Stanley Miller in 1953 launched the ambitious hope that chemists would be able to shed light on the origins of life by recreating a simple life form in a test tube. However, the dream has not yet been accomplished, despite the great volume of effort and innovation put forward by the scientific community.
L'action catalytique des argiles sur la polymérisation des acides aminés en solution aqueuse a été étudiée. Les résultats rapportés par Katchalsky et coll. dans le cas de la polymérisation de l'analyl adenylate en presence de montmorillonite n'ont pu ètre reproduits. D'autres types d'activation des acides aminés ont été examines.
In order to confirm the results of previous experiments concerning the chemical behaviour of organic molecules in the space environment, organic molecules (amino acids and a dipeptide) in pure form and embedded in meteorite powder were exposed in the AMINO experiment in the EXPOSE-R facility onboard the International Space Station. After exposure to space conditions for 24 months (2843 h of irradiation), the samples were returned to the Earth and analysed in the laboratory for reactions caused by solar ultraviolet (UV) and other electromagnetic radiation. Laboratory UV exposure was carried out in parallel in the Cologne DLR Center (Deutsches Zentrum für Luft und Raumfahrt). The molecules were extracted from the sample holder and then (1) derivatized by silylation and analysed by gas chromatography coupled to a mass spectrometer (GC–MS) in order to quantify the rate of degradation of the compounds and (2) analysed by high-resolution mass spectrometry (HRMS) in order to understand the chemical reactions that occurred. The GC–MS results confirm that resistance to irradiation is a function of the chemical nature of the exposed molecules and of the wavelengths of the UV light. They also confirm the protective effect of a coating of meteorite powder. The most altered compounds were the dipeptides and aspartic acid while the most robust were compounds with a hydrocarbon chain. The MS analyses document the products of reactions, such as decarboxylation and decarbonylation of aspartic acid, taking place after UV exposure. Given the universality of chemistry in space, our results have a broader implication for the fate of organic molecules that seeded the planets as soon as they became habitable as well as for the effects of UV radiation on exposed molecules at the surface of Mars, for example.
Careful examination of the present metabolism and in vitro selection of various catalytic RNAs strongly support the RNA world hypothesis as a crucial step of the origins and early life evolution. Small functional RNAs were exposed from 10 March 2009 to 21 January 2011 to space conditions on board the International Space Station in the EXPOSE-R mission. The aim of this study was to investigate the preservation or modification properties such as integrity of RNAs after space exposition. The exposition to the solar radiation has a strong degradation effect on the size distribution of RNA. Moreover, the comparison between the in-flight samples, exposed to the Sun and not exposed, indicates that the solar radiation degrades RNA bases.
Mars is at the center of the field of astrobiology in many ways. Today's vigorous program of ongoing exploration is largely motivated by Mars's potential to harbor life at present or at some time in the past. But astrobiology as a discipline is about more than just finding out whether there is or ever was life on Mars or on other planets and satellites. It is about determining the governing principles behind whether life will originate on a given planet or whether it can survive if transplanted there; about what the mechanisms are by which planets and biota can and do interact with each other; and about determining which fundamental factors distinguish a planet that is habitable from one that is not.
We know that the Earth meets the environmental requirements for being habitable. In Mars, we have an example of a planet that evolved under different physical and chemical conditions, allowing us to see what effects these differences can have. Today, Earth has global-scale plate tectonics, and Mars does not. Earth has global oceans at its surface, and Mars does not. Earth has a climate conducive to the coexistence of the solid, liquid, and vapor phases of water, each of which affects the geology and geochemistry of the planet, and Mars does not. In finding out whether Mars has or ever had life, we obtain a second example of whether and how life can occur on a planetary body.
The European Astrobiology Network Association (EANA) coordinates and promotes astrobiology in the 17 European countries that are member of the organization. Astrobiology includes the study of the origin, evolution and distribution of life in the Universe. It is a multi-disciplinary science that encompasses the disciplines of chemistry, biology, palaeontology, geology, atmospheric physics, planetary physics and stellar physics. The open questions to be addressed and the steps ahead in cosmochemistry, star and planet formation, the chemistry of life's origin, the study of bacterial life as a reference and the search for habitats and biosignatures beyond the Earth are presented.
A novel isolated Langendorff perfused rabbit heart preparation with intact dual autonomic innervation is described. This preparation allows the study of the effects of direct sympathetic and vagus nerve stimulation on the physiology of the whole heart. These hearts (n = 10) had baseline heart rates of 146 ± 2 beats min-1 which could be increased to 240 ±11 beats min-1 by sympathetic stimulation (15 Hz) and decreased to 74 ± 11 beats min-1 by stimulation of the vagus nerve (right vagus, 7 Hz). This model has the advantage of isolated preparations, with the absence of influence from circulating hormones and haemodynamic reflexes, and also that of in vivo preparations where direct nerve stimulation is possible without the need to use pharmacological agents. Data are presented characterising the preparation with respect to the effects of autonomic nerve stimulation on intrinsic heart rate and atrioventricular conduction at different stimulation frequencies. We show that stimulation of the right and left vagus nerve have differential effects on heart rate and atrioventricular conduction. Experimental Physiology (2001) 86.3, 319-329.
The period of time during which life emerged on the primitive Earth has been narrowed thanks to the geological record and to a better understanding of the primitive terrestrial atmosphere and hydrosphere. Terrestrial life probably appeared between 4.0 and 3.8 billion years ago. The inventory of organic molecules of prebiotic interest that were likely to be present at that time is satisfactory except for the RNA sugar component, ribose. Delivery of extraterrestrial organic molecules is of special interest since it is a process that still occurs today. The existence of such an import process on the early Earth required only an atmosphere to decelerate the particles. Such an atmosphere existed 3.8 billion years ago, as illustrated by, for instance, the Greenland sediments.
Among these organic molecules processed by liquid water, some began to transfer their molecular information and to evolve by making a few accidental transfer errors. For the sake of simplicity – for chemists, prebiotic chemistry was simple – one is tempted to assume that the chemical information and the transfer machinery were provided by the same molecules. Self-replicating RNA molecules fulfill these requirements. However, RNA molecules are not really simple, and whether they started life on Earth is still questionable. Self-replicating RNAs are, by definition, autocatalytic molecules that transfer their linear sequence information by an accurate residue-by-residue copying process, thanks to the template chemistry of complementary strands. Other examples of short autocatalytic molecules capable of making more of themselves by themselves are known in chemistry.
Humans in every civilization have always been intrigued by their origin and by the question of the origin of life itself. During thousands of years, the comforting theory of spontaneous generation seemed to provide an answer to this enduring question. In ancient China, people thought that aphids were spontaneously generated from bamboos. Sacred documents from India mention the spontaneous formation of flies from dirt and sweat. Babylonian inscriptions indicate that mud from canals was able to generate worms.
For the Greek philosophers, life was inherent to matter; it was eternal and appeared spontaneously whenever the conditions were favorable. These ideas were clearly stated by Thales, Democritus, Epicurus, Lucretius, and even by Plato. Aristotle gathered the different claims into a real theory. This theory safely crossed the Middle Ages and the Renaissance. Famous thinkers like Newton, Descartes, and Bacon supported the idea of spontaneous generation.
The first experimental approach to the question was published in the middle of the 17th century, when the Flemish physician Van Helmont reported the generation of mice from wheat grains and a sweat-stained shirt. He was quite amazed to observe that the mice were identical to those obtained by procreation. A controversy arose in 1668 when Redi, a Tuscan physician, published a set of experiments demonstrating that maggots did not appear when putrefying meat was protected from flies by a thin muslin covering.
Six years after Redi's treatise, the Dutch scientist Anton Van Leeuwenhoek observed microorganisms for the first time through a microscope of his own making. From then on, microorganisms were found everywhere and the supporters of spontaneous generation took refuge in the microbial world.
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