Pre-biotic

The hypothesis that our biological world built on the DNA-RNA-protein central dogma was preceded by an RNA world in which RNA molecules carried both the genetic information and executed the gene functions (through ribozyme activity) is now widely accepted [130]. However, it is also well recognized that RNA due to its vulnerability to hydrolysis - especially as a result of catalysis by divalent metal ions - would not have been able to evolve in a harsh pre-biotic environment Also the formation of RNA under presumed pre-biotic conditions is extremely inefficient It is not so far-fetched to propose that a peptide nucleic acid-like molecule may have been able to function as a form of pre-biotic genetic material since it... 

This is a serious matter for further thinking and could have implications for pre-biotic chemistry and eventually, for the origin of life. 

Rice bran fiber has fructo-oligosaccharides - a pre-biotic that helps friendly bacteria to proliferate in the gastrointestinal environment and improves intestinal and colon health (Tomlin and Read, 1988). Recent studies in humans (Kahlon and Chow, 1997) have revealed that rice bran fiber not only normalizes bowel function, but also helps in conditions such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and Crohn s disease, and lowers the lipid levels. Rice bran fiber has been shown to significantly reduce renal stones (Jahnen et al., 1992). It is a good source of fiber in weight loss programs and therapeutic fiber diets for diabetics and heart patients. Fiber diets prevent cancer of the colon and large bowel, control obesity and improve bowel function. 

In the same year, Miller and the biologist Antonio Lazcano (National Autonomous University of Mexico) spoke out against hypotheses that life could have originated at hydrothermal vents. They believe that the presence of thermophilic bacteria (the oldest life forms) does not prove that biogenesis occurred in the depths of the oceans. Stanley Miller sees a greater chance for successful pre-biotic chemistry under the conditions of a cold primeval Earth rather than at high temperatures in hydrothermal regions (Miller and Lazcano, 1995). 

A new dimension in the development of nucleic acid based catalysts was introduced by Breaker and Joyce in 1994 when they isolated the first deoxyribozyme [111]. It is not unexpected that DNA is also able to catalyze chemical reactions because it was shown previously that ssDNA aptamers which bind to a variety of ligands can be isolated by in vitro selection [141]. In the meantime, several deoxyribozymes have been described which expand the range of chemical transformations accelerated by nucleic acid catalysts even further and raising question whether even catalytic DNA might have played some role in the pre-biotic evolution of hfe on earth [69-71]. 

HV161 Kanauchi O., I. Serizawa, Y. Araki, et al. Germinated barley foodstuff, a pre-biotic product, ameliorates inflammation of colitis through modulation of the enteric environment. J Gastroenterol 2003 38(2) 134-141. 

Since ancient times, philosophers have wondered whether life on Earth was seeded from elsewhere in the universe, an idea known as panspermia. It is generally agreed that meteorites and comets contain pre-biotic compounds that could have provided the raw material for life on Earth. A more contentious question is whether the comets might actually contain microscopic organisms, as proposed by Hoyle and Wickramasinghe (1981). This hypothesis has not been taken seriously by most scientists, although it is hard to disprove. 

Additional advantages of the formamide condensation protocol were observed performing the reaction in the presence of catalysts which decompose formamide to formaldehyde. Formaldeyde is the most important pre-biotic precursor of sugars through a series of enolization and aldol-like condensation processes catalyzed under acidic or basic conditions, known as the formose reaction [100]. When formamide was heated at 160 °C in the presence of titanium dioxide (a catalyst able to degrade amides to aldehydes) [101] a complex mixture of nucleobase derivatives was obtained including adenine 1, purine 12, cytosine 17, N9-formylpurine 28, N9, N6-diformyladenine 29, 5-hydroxymethyluracil 30, thymine 31 and three novel... 

I am sure that the modelers who are doing a one-dimensional model in which the rate of transport is the rate of transport that is calculated to fit species in the current atmosphere, when they start applying this to a remote atmosphere, a very different circumstance, it is not at all clear that the transport rate ought to be even similar to the one that one has now. What I wonder if you have done is to take the composition of the existing atmosphere rather than a hypothetical pre-biotic atmosphere, and put in 300 times or 10 times ultraviolet, see what it does to the existing atmosphere and whether the then radiation transfer characteristics of that atmosphere would be appreciably different from the present atmosphere. Then you already have the parameter you are changing the atmosphere but you are assuming that the transport characteristics are exactly the same as this atmosphere. 

Crittenden R (2006) Emerging prebiotic carbohydrates. In Gibson GR, Rastall RA (eds) Pre-biotics Development and Applications. Wiley, Chichester, UK... 

These can include self-condensation to give peptides (in the case of the free amino acids) and cyclisation of amino-acid derivatives to give heterocyclic compounds. Controlled peptide synthesis is discussed later (Chapter 7), but the extraordinary ease of self-condensation of amino acids in concentrated aqueous NaCl containing copper(II) salts deserves mention (Saetia et al., 1993) since it suggests a way through which pre-biotic peptide synthesis may have come about. 

Effect of intestinal microbial flora, antibiotics, pro- and pre-biotics, and microbial vaccinations in the development of sensitisation and clinical manifestations of allergy. 

See comparison tables offered in J. T.-F. Wong and P. M. Bronskill. Inadequacy of pre-biotic synthesis as the origin of proteinaceous amino acids. Journal of Molecular Evolution, 13 (1979), 115-25. 

A. Keefe and S. L. Miller. Potentially pre-biotic syntheses of condensed phosphates. Origins of Life and Evolution of Biospheres, 26 (1996), 15-25 but see also D. Glindemann, R. M. de Graaf and A. W. Schwartz. Chemical reduction of phosphate on the primitive earth. Origins of Life and Evolution of Biospheres, 29 (1999), 555-61. 

Anders, E. (1989). Pre-biotic organic matter from comets and asteroids. Nature, 342, 255-7. 

In this context, the term absolute refers not to the formation of products in quantitatiye optical yields, but rather to the fact that such processes generate optically actiye products without the imposition by man of any external chiral influence. Absolute asymmetric syntheses are therefore obyious candidates for explanations of how optical actiyity could haye arisen under pre-biotic conditions, and this aspect of the subject has been discussed (4b, 6). 

Through these simulations, students appreciate the energetic and kinetic aspects of chemical reactions and why the composition of the atmosphere is critical to the outcome. For example, the class simulates the effect on the yield of amino acids if the atmospheric composition was CO2 instead of CH4 or the nitrogen source was N2 instead of NH3. The simulations also allow students to investigate the consequences if the pre-biotic atmosphere contained free 02. Through these simulations, basic chemical concepts are discussed including thermodynamics, thermochemistry and bond enthalpies, kinetics, and catalysis. 

Figure 10.1 The foundations of pre-biotic chemistry showing the "starting materials", the means of provoking reaction and a summary of main elemental compounds produced.

Figure 10.2 Interstellar gas cloud (TITAN s atmosphere) "starting materials" for pre-biotic chemistry, compared with the compounds that result from electrical discharge in an atmosphere of N2 and CH4. Note the extraordinary compatibility between these lists ...

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