Life, origins

Genesis of nucleic bases, nucleotides, and nucleosides the problem of RNA origin and its role in life origin 99T3141. 

It is significant that the earliest records of life on Earth start shortly after the period of impact frustration. Apparently life formed as soon as the conditions permitted it. Life originated from compounds produced by prebiotic organic chemistry. The source of the molecules included those produced on Earth by energetic processes such as impacts and electrical discharges as well as those that fell in from space. Whatever processes occurred, they would have had to happen either in the deep ocean or in what might have been rare regions of land and shallow water. 

Scientists do not believe that life is arising from non-life on Earth today, but, if life originated on Earth, as it apparently did, it must have developed from non-living materials. Current scientific views of when and how life might have originated and evolved are based upon imaginative chemical experiments in the laboratory, combined with studies of the fossil record and ways of dating events in the remote past. 

Iron is the most abundant, useful, and important of all metals. For example, in the 70-kg human, there is approximately 4.2 g of iron. It can exist in the 0, I, II, III, and IV oxidation states, although the II and III ions are most common. Numerous complexes of the ferrous and ferric states are available. The Fe(II) and Fe(III) aquo complexes have vastly different pAa values of 9.5 and 2.2, respectively. Iron is found predominantly as Fe (92%) with smaller abundances of Fe (6%), Fe (2.2%), and Fe (0.3%). Fe is highly useful for spectroscopic studies because it has a nuclear spin of. There has been speculation that life originated at the surface of iron-sulfide precipitants such as pyrite or greigite that could have caused autocatalytic reactions leading to the first metabolic pathways (2, 3). 

Life originated in an aqueous environment enzyme reactions, cellular and subcellular processes, and so forth have therefore evolved to work in this milieu. Since mammals live in a gaseous environment, how is the aqueous state maintained Membranes accomplish this by internalizing and compartmentalizing body water. 

Chemists would like to invent molecules that assemble themselves into specific, we 11-organized arrays. Recently there have been some exciting successes. Our inset is a molecular view of a self-assembled molecular wreath. This organized sfructure forms when four molecular chains weave themselves together in the presence of 12 copper cations. Self-assembling molecular systems could lead to new materials with useful properties. They may also shed light on how life originated. 

Trevors, J. T. and Abel, D. L. (2006) Self-organization vs. self-ordering events in life-origin models. Phys. Life Rev., 3, 211-228. 

Hartman, H. (1998). Photosynthesis and the origin of life. Origins Life Evol. Biosphere, 28, 515-521... 

There is no one correct theory for the origin of life on Earth or any habitable planet, although many have been presented. The current set of ideas is summarised in Figure 1.5. Aside from the theory of creation, which seems particularly hard to test, the testable theories of the origins of life divide into two extraterrestrial or panspermia, the theory that life was seeded everywhere somewhat randomly and terrestrial, that life originated de novo on Earth or other habitable planets around other stars. The theories of terrestrial origin are more favoured but the recent discovery of habitable planets and life within any solar system suddenly makes panspermia more likely. 

The main assumption held by most scientists about the origin of life on Earth is that life originated from inanimate matter through a spontaneous and gradual increase of molecular complexity. 

Creationists apart, the view that life originates by itself from inanimate matter is rich with important implications for the philosophy of science and life at large. It is therefore important in our discussion to pause and consider this view, the underlying conceptual framework, as well as some of the consequences. 

Life originated from inanimate matter as a spontaneous and continous increase of molecular complexity. Chemical continuity principle - no transcendental principle. 

Even if we are not able to explain how life originated on Earth, we may be able to give a good answer to such questions. This is satisfactory enough and a great motivation for the next generation of life scientists. 

It is astonishing that the potassium ion plays such an important role in biochemistry, although it was present in only low concentration in terrestrial surface waters when life originated around 1017s ago. 

Life originated about 3.5 billion years ago, most likely with the formation of a membrane-enclosed compartment containing... 

It is also not clear that terran life originated on Earth in the chemical form that we know now. Respectable hypotheses suggest, for example, that the three-biopolymer (DNA-RNA-proteins) system that characterizes all life that we know on Earth, a system in which nucleic acids serve roles predominantly in genetics and information transfer and proteins serve roles predominantly in catalysis, may not have been characteristic of life as it first originated. Only one of these complex chemical entities may have been represented in primitive life, or perhaps none at all. 

Holm, N.G. 1992. Why are hydrothermal systems proposed as plausible environments for the origin of life Origins Life Evol. Biosph. 22 5-14. 

Given that interstellar ices are the building blocks of comets and comets are thought to be an important source of the species that fell on primitive Earth, the structures of molecules in comets may be related to the origin of life. It is possible that organic materials formed in the solid ice phase of interstellar materials provided raw materials used for life originating solely on Earth. If so, the deep freeze of ice in the Oort cloud would have been an excellent place to store these, especially the unstable ones, awaiting delivery to a planet. 

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