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At least 397 records · Page 22Linked to original sources
PubMed2001

Self-assembling amphiphilic molecules: Synthesis in simulated interstellar/precometary ices.

Interstellar gas and dust constitute the primary material from which the solar system formed. Near the end of the hot early phase of star and planet formation, volatile, less refractory materials were transported into the inner solar system as comets and interplanetary dust particles. Once the inner planets had sufficiently cooled, late accretionary infall seeded them with complex organic compounds [Oró, J. (1961) Nature (London) 190, 389-390; Delsemme, A. H. (1984) Origins Life 14, 51-60; Anders, E. (1989) Nature (London) 342, 255-257; Chyba, C. F. & Sagan, C. (1992) Nature (London) 355, 125-131]. Delivery of such extraterrestrial compounds may have contributed to the organic inventory necessary for the origin of life. Interstellar ices, the building blocks of comets, tie up a large fraction of the biogenic elements available in molecular clouds. In our efforts to understand their synthesis, chemical composition, and physical properties, we report here that a complex mixture of molecules is produced by UV photolysis of realistic, interstellar ice analogs, and that some of the components have properties relevant to the origin of life, including the ability to self-assemble into vesicular structures.

Astronomy↗
PubMed1992

Chemical markers of prebiotic chemistry in hydrothermal systems.

The goal of this chapter is to suggest some organic compounds which may be indicative of prebiotic processes in hydrothermal systems or laboratory simulations of them. While the exact processes which led to the origins of life are not known, studies of life's origins of the past forty years have uncovered a plethora of potential precursor molecules. Some of these same molecules were probably present in hydrothermal systems if chemical processes there had a role in the origins of life. The types of molecules formed in primitive Earth simulation experiments and observed in the interstellar medium, on comets and meteorites will be reviewed in Section 2 of this chapter. Some reactions involving these molecules which may have been important in prebiotic syntheses will be outlined. Since near- to supercritical water is found in hydrothermal systems, its properties and aspects of organic chemistry in supercritical water at high temperature and pressure will be discussed in Section 3. Fischer-Tropsch type (FTT) reactions, which are a potential source of the building blocks of biological molecules in hydrothermal systems, are discussed in Section 4. In the concluding section, Section 5, the possible formation in hydrothermal systems of organic molecules that are believed to have been important for the origins of life is discussed.

Chemistry, Organic↗
PubMed2000

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.

Animals↗
PubMedDate not supplied

[N. A. Umov's physicomechanical model of living matter (on the 150th anniversary of his birth)].

In 1901, N. A. Umov described his physicomechanical model of living matter and later continued to develop it as the most important element of his scientific picture of the world. The model contains a definition of life, an indication of the source of living matter activity, analysis of the entropy to evolution ratio and the role of entropy in the evolution of psychics, and the principles of theoretical biology, including the principle of preservation of the amount of living matter during evolution. The Universe as a whole is proposed as a guarantor of life origin.

Animals↗
PubMed2006

From volcanic origins of chemoautotrophic life to Bacteria, Archaea and Eukarya.

The theory of a chemoautotrophic origin of life in a volcanic iron-sulphur world postulates a pioneer organism at sites of reducing volcanic exhalations. The pioneer organism is characterized by a composite structure with an inorganic substructure and an organic superstructure. Within the surfaces of the inorganic substructure iron, cobalt, nickel and other transition metal centres with sulphido, carbonyl and other ligands were catalytically active and promoted the growth of the organic superstructure through carbon fixation, driven by the reducing potential of the volcanic exhalations. This pioneer metabolism was reproductive by an autocatalytic feedback mechanism. Some organic products served as ligands for activating catalytic metal centres whence they arose. The unitary structure-function relationship of the pioneer organism later gave rise to two major strands of evolution: cellularization and emergence of the genetic machinery. This early phase of evolution ended with segregation of the domains Bacteria, Archaea and Eukarya from a rapidly evolving population of pre-cells. Thus, life started with an initial, direct, deterministic chemical mechanism of evolution giving rise to a later, indirect, stochastic, genetic mechanism of evolution and the upward evolution of life by increase of complexity is grounded ultimately in the synthetic redox chemistry of the pioneer organism.

Archaea↗
PubMed2005

An explanatory model of health promotion and quality of life for persons with post-polio syndrome.

Although previous studies have examined selected factors influencing health promoting behaviors or quality of life, the complex interplay of these variables in persons with different chronic disabling conditions has not been investigated. This study tested an explanatory model of variables influencing health promotion and quality of life originally developed with a sample of persons with multiple sclerosis in a new sample of persons living with post-polio syndrome (PPS) in the USA. The sample of 1603 persons with PPS (1123 females, 478 males and 2 unknown) completed a battery of instruments including measures of severity of polio-related impairment, barriers to health promoting behaviors, resources, self-efficacy, acceptance, health promoting behaviors and perceived quality of life. A model originally developed in a sample of 786 persons with multiple sclerosis was assessed and modified using the weighted least squares procedure (WLS) which is implemented by LISREL8. The structural equation analyses resulted in a proper solution that exhibited adequate fit: chi2 (8, N = 1549)=84.22, p<0.05; GFI=0.96, IFI=0.90, CFI=0.90. The antecedent variables accounted for 65% of the variance in the frequency of health promoting behaviors and 53% of the variance in perceived quality of life. The model test supports the hypothesis that quality of life is the outcome of a complex interplay between contextual factors (severity of impairment), antecedent variables, and health promoting behaviors. It also suggests that the relationships among these variables are similar in samples of persons with two different chronic conditions. Further research using a qualitative approach is needed to clarify other contributors to quality of life in persons with post-polio syndrome.

Activities of Daily Living↗