The Origin of life (abiogenesis) | The Bridge Between In-organic(lifeless) and Organic(life)PHYSIOLOGY: The Science of Human Function

Title: The Origin of life (abiogenesis) | The Bridge Between In-organic(lifeless) and Organic(life) Author: Yinka Okunlola

Subject: Science

Language: English

Source: Steemstem Project

Introduction

The origin of life has been the greatest myth of the universe. Life being the mystery behind every living creature regardless its identity or personality, has been a very hard nut to crack when it comes to defining it, and locating its origin. Life might sound simple but it goes a long way differentiating the living from the non-living. But how does the living acquire this distinct quality? This is a question that has cost many philosophers and scientist their lifetime trying to puzzle out. So let’s see how science has been able to explain the phenomenon behind Life.

Early Belief

The story of how the world comes to form or how life first existed on it is as diverse as the number of cultures of the world. Almost every culture has a way of defining their origin. But something common among these stories is a belief that all creations are made by a magnificent supreme being. They believe the earth and all that is in it were created by a celestial mighty being, “god”. This was even strengthened by the western theological belief according to the biblical record of creation. The first book of the bible (Genesis) recorded that the earth and everything on or in it was created by Almighty God over a period of six days. For many years , The majority of the communities of the world held on to this mythological belief until the middle of the nineteenth century, when it becomes clear that living organisms are subjected to the same physical and chemical laws just as non-living things. Does that mean they have the same origin as the non living things?

Basics of Life

As popularly defined, Life or living system is any system that posses the ability to metabolize; eat, breath, sense, grow, excrete, reproduce and die.

licence: Public domain Source: wikimedia

Every living organisms are made of basic bio-organic molecules which are formed by elementary ingredients. These bio-molecules include Protein that serve as the building blocks of bio-structures; Carbohydrate which serve as source of energy; Lipids which forms the major components of cell membranes; and Nucleic acids that houses and translate genetic code. These molecules are not living things themselves but are formed from combinations of basic elements. They are formed by six basic elements that combine naturally in a correct bonding arrangement to form simple molecules and thereafter complex polymers. These Basic elements include; carbon (C), Hydrogen (H), Nitrogen (N), oxygen (O), Phosphorus (P) and sulfur (S ) and when bind in the right order they form structures that define the skeleton of bio-molecules.

Preceding Theories

https://upload.wikimedia.org/wikipedia/commons/f/f2/Thales\_of\_Miletus.jpg
licence: Public domain Source: wikimedia

Dating back to the ancient Greek, a trend of successive philosophers has questioned the belief behind the emergence of the physical world. They diverge from the preliminary mythological knowledge and focused on practical knowledge in making philosophical assumption. These philosophers viewed the concept of origin of life from two perspectives; the monistic and the pluralistic view. The monists assumed that the origin of the world is from a single substance while pluralists held to the belief that creation would have been from a mixture that exhibit random motion and having its particles collide, bind and separate thereby forming life by "Chance". The Greek philosopher “Thales of Miletus” was the first to give a pure natural explanation of the origin of the world independent of mythological abstract. He assumed that life had emerged from water.

Early Hypothesis : Oparin-Haldane Soup Theory

The basic and fundamental theory of the origin of life was proposed by two scientists; Russian chemist Alexander I. Oparin and British scientist John B. Haldane in the 1920s.

Aleksandr Oparin (right) in enzymology_laboratory
licence: Public domain Source: wikimedia

They both suggested that the earth’s early atmosphere does not contain oxygen (O2) and this cause it to be very reactive. The absence of oxygen defines the difference between the earth’s early atmosphere and the modern atmosphere we have today. It is explained that the oxygen present in the modern atmosphere prevents the formation of a subsequent life like that of the first and even if it seems to occur, they are being fed on by the already existing living organisms. The hypothesis suggested that life could have emerged from a very reducing atmosphere of an heated aqueous mixture that forms the Primordial Soup, in the presence of energy from ultraviolet radiation or massive lightening. This reaction passes through different stages of complexity to form simple organic monomers. According to this hypothesis, John D. Bernal, an Irish scientist, summarizes the process of biosynthesis (origin of life) in 1949 in three stages; - Origin of biological monomers - Origin of biological polymers - Evolution from molecules of cells The hypothesis of “Soup Theory” stated by Oparin and Haldane was supported by an experiment by Stanley L. Miller and Harold C. Urey in 1952 to demonstrate how organic molecules are formed from primordial inorganic ingredients.

Millar-Urey experiment

Being that the Oparin-Haldane’s hypothesis was widely accepted , it served as a framework from other succeeding research.

https://upload.wikimedia.org/wikipedia/commons/d/d9/Miller1999.jpg
licence: Public domain
Source: wikimedia

The test to this hypothesis was conducted by Stanley Miller with the assistance of Harold Urey with the contraception of the conditions suggested by Oparin and Haldane: a reducing atmosphere ( a very reactive environment), Lightening and a nutrient rich ocean. They end-up creating what could satisfy these conditions. The experiment was performed with an apparatus of a sterile 5-liters glass flask connected to a 500ml flask. The 500ml flask was half filled with Water(H2O), and Methane(CH4), Ammonia (NH3) and Hydrogen(H2) are added through the gas inlet into the circulation. The water in the flask was heated and a continuous electric sparks were fired between the electrodes in the 5-liter glass to simulated lightening in the water vapour and gaseous mixture. The simulated atmosphere pass through a condenser to be cooled and trickled into a U-shaped trap.

https://upload.wikimedia.org/wikipedia/commons/thumb/5/54/Miller-Urey\_experiment-en.svg/644px-Miller-Urey\_experiment-en.svg.png
licence: CC-BY-SA Source: wikimedia

This cycle continues for as long as one week and the solution which represents the Primordial Soup is collected, purified and analyzed. By analysis it was found that about 10% - 15% of the carbon in the system was then in form of a mixture of organic compounds consisting of amino acids. Miller identified five amino acids in the solution; glycine, alanin, alanin, aspartic acid and amino butyric acid.

Further Experiments and Modifications

The Urey-Miller experiment is regarded as the classic experiment in investigating the origin of life. Although the experiment vividly support the Oparin hypothesis but did not end the journey, on the contrary, it serves as a poke for new ideas and experiments. Recent investigation and experiments have created rooms for ideas, hypothesis and discoveries that get the story more complicated. - Examination of the extract from miller’s experiment with advanced analytical procedures showed more amino-acids than was initially discovered by miller. - Wolman N. MacNevin (at the Ohio University) discovered biochemicals relating to earth’s early primordial molecules while performing an experiment similar to that of miller (although he did this independent or ignorant of any theory of evolution). He was passing 100000 volt spark through methane and water vapour. - Experiment performed by Jeffrey Bada- adding iron and carbonate minerals to the initial ingredients of the miller’s experiment. The products were very rich in amino acids. This suggest that the early atmosphere might contain carbondioxide and Nitrogen. - In 1961, Joan Oro discovered that RNA and DNA nucleobases as well as amino acids could be obtained through simulated prebiotic chemistry with a reducing atmosphere. This suggest RNA world hypothesis which proposed that RNA being able to serve as a gene carrier and enzyme could have been the basis of pre-cellular life. >Based on these subsequent experiments it is very clear that there is no difficulty in synthesizing or forming the molecules that are necessary for life from their inorganic precursors. However J.D. Bernal concluded that “It is not enough to explain the formation of such molecules, what is necessary is a physical chemical explanation of the origin of these molecules that suggest the presence of suitable sources that sinks for free energy.

Conclusion

Many scientist have spent their lifetime trying to unravel the principle behind the phenomenon that bridge between the non-living molecules and the living organism. Yet no one has been able to obtain the characteristic called Life by combining these elementary molecules.

References:

- Abiogenesis: https://en.wikipedia.org/wiki/Abiogenesis - Definition of Life: https://www.britannica.com/science/life - Ingredients of Life: https://www.livescience.com/32983-what-are-ingredients-life.html - Basic Molecules of Life: https://basicbiology.net/biology-101/molecules-of-life/ - Oparin-Haldane Hypothesis: https://en.wikibooks.org/wiki/Structural\_Biochemistry/The\_Oparin-Haldane\_Hypothesis - Miller-Urey Experiment: https://en.wikipedia.org/wiki/Miller%E2%80%93Urey\_experiment - Oparin-Haldane Hypothesis: https://en.wikibooks.org/wiki/Structural\_Biochemistry/The\_Oparin-Haldane\_Hypothesis ------

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