Metabolism and Emergence of 1st Life

In 1953, a historical experiment was conducted on the origin of life on Earth. Stanley L. Miller and Harold C. Urey of the University of Chicago attempted to actually reproduce the theory of Scottish scientist John B. S. Haldane and Aleksandr N. Oparin of Russia in the early 20th century. According to the Haldane-Oparin hypothesis, primitive earth had good conditions for inorganic compounds to be synthesized as organic compounds. In order to imitate the primitive earth, a loop type laboratory apparatus consisting of a sterilized glass tube and a flask filled with water vapor, methane, ammonia, and hydrogen was used. One flask is half filled with water and the other contains a pair of electrodes. The water was heated to vaporize, sparkling in the air containing water vapor, and mimicking natural lightning. Then, again, the air is cooled, the water vapor becomes water, and the process of returning to the first flask is repeated.

Miller-Urey experiment (1953) from Wikipedia

After a week of continuous experimentation, Miller and Urey observed that between 10 and 15% of the input molecules were synthesized into organic materials. Of these, 2% of the carbon was obtained in the form of several kinds of amino acids that constitute proteins of living cells. It would show that a part of the order we recognize as living is thermodynamic order inherent in the geosphere. Miller's experiment produced 13 of the 20 amino acids used in life, and it is important to first discover the process by which organic matter is formed from inorganic molecules. Miller's experiments were continuously reproduced through various subsequent experiments. In 2014, it was confirmed that other organic materials other than amino acids were also synthesized through RNA synthesis experiments.

Then, how could this happen in primitive earth? The lightning and storms of the primordial Earth simultaneously cause the flow of material and the flow of energy between two reservoirs of different potentials. Without lightning and storms, the circulation of matter and energy would have moved through diffusion, and movement by diffusion would have easily reached equilibrium through resistance.

Two of the most important abiotic processes are the energy activities that take place when electrons are exchanged between molecules created by geothermal chemistry and generating oxidants and reductants through the process of converting the energy of light coming from the sun. When there was no organism, the energy of the primordial earth would have remained unused except for some radiation processes. For example, the reaction of a hydrogen molecule, a reductant, with carbon dioxide, an oxidant, does not happen very well. If these molecules were not consumed by living organisms, these molecules produced by geothermal processes would have accumulated continuously. Similarly, if inelastic absorption of light was accumulated, the molecule would have absorbed energy as a result of photo-dissociation phenomena losing one or more atoms. In addition, light is absorbed into the heat through the inelastic scattering of the Earth's oceans, becoming the primary driver of the global weather system. However, this process could not concentrate enough energy to produce a large-scale chemical transformation of the earth. However, this primitive earth situation has become the driving force for the optimized flow and channel of the energy source, called metabolism.

Molecules rich in earth, storms, lightning, and intense energy sources spawn various forms of metabolism cycles, some of which have made a significant contribution to the birth of life. Among them, the hydrolysis of high-energy ester bonds of phosphate polymers has served as an energy supplier for many metabolisms. And, many cascade of metabolism made through this functioned as a relaxation channel of geochemical energy and electronic transfer of reductants was done. Among the various metabolic cycles, the citric-acid cycle is involved in the formation of spontaneous 2 to 4-carbon compounds, in which the carbon atoms of the intermediates produced through this cycle are not completely reduced and subsequently release fatty acids and acetate. In addition, the formation of sugars, amino acids, and other compounds creates pathways to hydrolize phosphate esters or incorporate ammonia. In other words, the main metabolisms of carbon are finally converted to the form of fully oxidized carbon dioxide, or, conversely, converted to the most reduced form of methane, but some are incorporated into biomass such as fatty acids, sugars, amino acids, nucleotides, and cofactors. And, they became the platform of further metabolism afterwards. These biochemical intermediates become a kind of bootstrap process, which can form a network of diverse molecules, especially ammonia and phosphate reacted with the starting compounds.

Non-living earth would be in constant instability under conditions of continuous geochemical free energy production. In this process, life emerged and suddenly became stable. Membranes composed primarily of phospholipids accumulate internal organic reagents for metabolism and form cells in a way that maintains create pH and voltage differences. As they convert redox to phosphate energy, they use them to segregate polar and non-polar environments in which different biochemical reactions are favored. In this respect, cells can be said to exist as the most productive platform for metabolism. Here, characteristics of individuality and heritable variation are born. This means that life is ultimately the confederacy of chemical constructs and pathways, functions.

Let's organize. The environment of the primordial Earth was a continual mix of energy and solar energy, with carbon-based minerals and various molecules present in the flow of lightning and storms. The explosive flow of energy has led to the birth of a cycle called metabolism, in which the earth quickly began to balance. Among them, primitive cells appeared in the form of cell membranes composed mainly of phospholipids.

From the perspective of information, carbon-based materials with various seeds of information have diverse flows through the energy of the sun and earth, and various circuits called metabolism have begun to be constructed. And this process of metabolism was able to supply energy through a kind of battery through the hydrolysis of phosphates, and with the birth of the cell membrane, this metabolic process could be done inside the cell. Now, as the inside and the outside of the cell are separated, each of these cells can operate as an independent module, and various types of replication have begun to enter the competition to maintain and spread their information.

How, then, could it be possible to replicate and convey this information over and over again? Life creates a sophisticated way of doing this. This is the topic of the next post.


New insights into prebiotic chemistry from Stanley Miller's spark discharge experiments
Energy Flow and the Organization of Life


Popular Posts