Origin, of life

One of the major gaps in our knowledge concerns how the organic compounds that were synthesized 

Most scientists speculate, however, that the first organisms were bacteria, and most agree with Oparin s (1938) hypothesis that they were hetero-trophic, i.e. they obtained their energy by oxidizing organic compounds. Indeed, the first bacteria are viewed by some as being very similar to the anaerobic fermentative bacteria. 

One example of fermentative bacteria is a group termed the lactic acid bacteria. These bacteria, which are commercially important in the cheese and dairy industry as well as in pickle and sauerkraut production, produce lactic acid by fermenting sugars. 

This simple metabolic process occurs anaerobically by a series of enzymes involved in a pathway called glycolysis (Fig. 3-4), in which glucose, a 6-carbon sugar, is converted ultimately to p)rruvic acid. Initially, the glucose is phosphorylated by the enzyme hexokinase which requires ATP (adenosine triphos- 

A summary of the literature of silica biogeochemistry was presented by Leo and Barghoorn (4b), who discussed the cyclical movements of silica, including passage through the biosphere.  

In this chapter some of these aspects are reviewed briefly. Attention is concentrated on the chemistry of soluble and colloidal silica in relation to interaction with biochemicals and biocolloids. 

In many biological studies, data are given in terms of silicon rather than silica. Since there is little evidence that silicon occurs in any biosystem in any form other than in coordination with oxygen, data are referred to here in terms of silica or SiO,. 

The fossilization of life forms has already been described in Chapter 1 since there is no biochemical involvement of silica. 

Even though silicon is one of the most abundant elements, it has been considered to be nonessential in most living organisms, whereas carbon, which is far less plentiful, is the primary element upon which all life depends. 

What is life . This is not as easy to define as we might like Life has several properties, none of which are unique or defining, but which together contribute to our understanding of living thing. Life is  

So when does the first evidence of improbable, information-containing, metabolic replication occur in the fossil record The Earth is 4,500 million years old, as judged by several corroborating radionuclide studies of the oldest rocks on the planet show. Meteoric bombardment of the proto-Earth continued heavily until 4,000 MY A, probably precluding life during this period. The majority of the oldest rocks on Earth are 3,500 million years old, and the earliest microfossils are from 3,000+ MYA, hence we only have a window of about 500 million years from the end of the meteoric bombardment to the first signs of microbial life. This means we are either very lucky, or life is a high-on certainty  

What did life use as its raw materials Early theories of life s origins thought that tire earth had a reducing atmosphere i.e., lots of ammonia and methane) but this 

The formation of polymers is more problematic. A major difficulty is that biopolymers are all thermodynamically unstable relative to their hydrolysis products. Some theories, but no certainty as to how polymers may have formed, though polymers have been synthesized under conditions which may have occurred on the early Earth. 

The biggest problem for the origin of life is the issue of how we go from polymers to living systems.  

The problems related to life s origin in the Earth are central and crucial in any discussion of biogeochemical evolution. Theoretical and experimental analyses of the origins of life occupied a considerable fraction of human thoughts and efforts. Until now it remains the central problem of many sciences, from theosophy to biology. 

CO2 photolysis occurring in the upper atmosphere produces O2 which can fix hydrogen back into water. The presence of oxygen in even small concentrations (10 ), however, would inhibit the formation of more complex organic molecules due to CO formation (and subsequent CO2) as proposed for the origin of life (the Miller-Urey hypothesis see Chapter 2.2.2.1). 

The photolysis of carbon dioxide (beside that of water) also provides small amounts of oxygen (and related radicals). Hence, the presence of CO2 and H2O as well as UV radiation can also produce simple hydrocarbons. As mentioned, strong UV radiation limited the synthesis of more complex molecules and radical reactions led back to the radiative relatively stable molecules CO2 + H2O. 

The following main elementary reactions are behind the above scheme (Eq. 2.35, cf. also 2.33)  

Only with the occurrence of photosynthesis about 2.7 Gyr ago, was O2 available in a stepwise excess (compared to the low photolytic production in air), but first it was consumed by oxidizing Fe and other reduced compounds. Only after reaching a redox equilibrium did the seawater become saturated with O2 and oxygen may have escaped to the atmosphere. This certainly had quite an impact on further evolution. Small amounts of oxygen abiotically produced in the atmosphere had been tolerated for the first 2.5 Gyr. Besides free oxygen in the lower atmosphere, oxygen was deposited due to oxidation of reduced materials on the crustal surface of the continents. 

If water was as common in the solar system as is implied by the facts presented in Chapter 2.1, then that would suggest that there were many environments in the solar system where the conditions were right for the development of life. What is life For instance, Lynn Margulis (quoted by Morgan 1997) has stated that to pro- 

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Once the broad outlines of DNA replication and protein biosynthesis were established scien tists speculated about how these outlines af fected various origins of life scenarios A key question concerned the fact that proteins are re quired for the synthesis of DNA yet the synthesis of these proteins is coded for by DNA Which came first DNA or proteins How could DNA store genetic infor mation if there were no enzymes to catalyze the polymerization of its nucleotide components How could there be proteins if there were no DNA to code for them ... 

After retirement he went to the Centre for Theoretical Studies at Coral Gables, Florida, where one of his main interests was the question of the origin of life. He died at Coral Gables on October 5, 1976. 

Early students of the origin of life were misled because they believed that Earth was very young, in part because no methods were available for dating ancient events. Today, suitable methods exist for determining the age of materials that are billions of years old, and the fossil record of ancient organisms has vastly improved. The evolution of living organisms... 

Archean 3.8 Gyr Origin of life prokaryotes flourish. Photosynthetic cells liberate oxygen, O2 first appears in the atmosphere... 

Chang, S., Desmarias, D., Mack, R., Miller, S. L., and Strathem, G. E. (1983). Prebiotic organic synthesis and the origin of life. In "Earth s Earliest Biosphere, Its Origin and Evolution" (J. W. Schopf, ed.), pp. 53-88. Princeton University Press, Princeton, New Jersey. 

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

In addition to the catalytic action served by the snRNAs in the formation of mRNA, several other enzymatic functions have been attributed to RNA. Ribozymes are RNA molecules with catalytic activity. These generally involve transesterification reactions, and most are concerned with RNA metabofism (spfic-ing and endoribonuclease). Recently, a ribosomal RNA component was noted to hydrolyze an aminoacyl ester and thus to play a central role in peptide bond function (peptidyl transferases see Chapter 38). These observations, made in organelles from plants, yeast, viruses, and higher eukaryotic cells, show that RNA can act as an enzyme. This has revolutionized thinking about enzyme action and the origin of life itself. 

Singer, T. P. In Biochemical Evolution and the Origin of Life, p. 203 edited by Schoffeniels, E. Amsterdam North Holland 1971. 

The ability of STM to image at the atomic scale is particularly exemplified by the two other chapters in the book. Thornton and Pang discuss the identification of point defects at Ti02 surfaces, a material that has played an important role in model catalyst studies to date. Point defects have been suggested to be responsible for much of the activity at oxide surfaces and the ability to identify these features and track their reactions with such species as oxygen and water represents a major advance in our ability to explore surface reactions. Meanwhile, Baddeley and Richardson concentrate on the effects of chirality at surfaces, and on the important field of surface chirality and its effects on adsorption, in a chapter that touches on one of the fundamental questions in the whole of science - the origins of life itself ... 

In the earlier years, in the absence of exact knowledge of microorganisms or chemistry, there had arisen much skepticism and bitter feeling over the question of the origin of life. One scientist who still held to the ancient ideas says of the views of another who doubted,... 

For a fuller discussion of this view of the origin of life, see Rose (1997)-... 

The learning process with respect to the problem of the origin of life took place in a manner similar to the three stages described by the French philosopher Auguste Comte (1798-1857) for the linear history of progress in human culture. These three stages are ... 

The deciding impulse which introduced biogenesis into scientific discussion came from Russia. After the upheavals of the civil war, that country was the subject of worried observation by the rest of the world. It was assumed that no great scientific achievements would be possible there. Then, in 1924, a book on the material basis of the origin of life on Earth appeared in Red Russia . Its author was Alexandr Ivanovich Oparin (1894-1980) from the Bakh Institute of Biochemistry in Moscow (Oparin, 1924). Basically, the Oparin hypothesis makes the following assumptions ... 

Various definitions have been proposed, and, depending on one s scientific standpoint, a suitable one may be available. Several of these definitions will be presented below. A completely satisfactory answer will, however, probably only be found when more detailed results on the origin of life become available. 

Haldane JBS (1928) The Origin of Life. Rationalist Annual 148 3. Reprinted in Science and Human Life, Harper Brothers, New York, 1933 Herrera AA (1942) Science 96 14... 

Oparin AI (1924) The Origin of Life, 1. Edition (Russian Proiskhozdenic Zhizni). Moskovskiy Rabochii, Moskau... 

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