Biochemical Origin of Life

The genesis of life on Earth is linked to the origin of the cosmos. You are aware that the cosmos has structure. On a macro scale, it comprises superclusters, which are groupings of massive clusters. Clusters can comprise anywhere from a few galaxies to thousands. The galaxies, in turn, are made up of stars, gas, and dust clouds.

Our star, the Sun, is just one of 100 billion stars in the Milky Way Galaxy. It is surrounded by nine planets, including Earth, which orbits it. Did you ever wonder, while reading this, how we got to know so much about the structure of the universe? Because all we can see with our naked eyes are a few thousand stars spread throughout the sky.

Biochemical Origin of Life

The issue of how life began in the first place remained unresolved. To discover an answer to this issue, we must go back billions of years and try to conceive what the world would have been like when life first arose. Certain factors made the genesis of life on Earth possible −

  • The origin of the solar system, including the Sun.

  • Chemical variety (hydrogen, nitrogen, sulfur, phosphorus, and carbon-containing compounds).

  • Water is present.

  • Earth cooling from its initial temperature of 5000-6000° C.

  • The availability of energy from solar radiations, cosmic rays, volcanic eruptions, stratified clays, and other sources on early Earth.

  • The presence of a lowering atmosphere.

Oparin-Haldane Theory of Origin of Life

In 1920, Alexender I Oparin, a Russian biochemist, and J.B.S. Haldane, a British biologist, postulated that life on early Earth arose through physicochemical processes of atoms combining to create molecules. In turn, molecules interacted to form inorganic and organic substances. Organic substances reacted to generate various types of macromolecules, which eventually organized to form the first living system or cell.

According to this view, life on Earth sprang spontaneously from non-living elements. In response to ever-changing environmental circumstances, inorganic molecules developed first, followed by organic compounds. This is known as chemical evolution, and it cannot occur under the current environmental circumstances on Earth. Only on the primitive Earth were conditions conducive to the genesis of life exist. Life's chemical evolution may be separated into four stages as −

Atomic Phase

The early Earth was abundant in atoms such as hydrogen, oxygen, carbon, nitrogen, sulfur, and phosphorus, which were required for protoplasm development. Atoms were classified into three concentric masses based on their weight. The heaviest iron, nickel, and copper atoms were concentrated in the Earth's core. Medium-weight atoms of sodium, sulfur, phosphorus, potassium, silicon, magnesium, aluminium, chlorine, fluorine, and other elements were concentrated in the Earth's core. The lightest atoms of nitrogen, hydrogen, oxygen, carbon, and other elements were predominant in the early atmosphere.

Formation of Inorganic Molecules

Hydrogen (H2), Nitrogen (N2), water vapour (H2O), methane (CH2), carbon dioxide (CO2), and ammonia are examples of essential inorganic compounds formed from free atoms. (NH2). In the early atmosphere, hydrogen atoms were the most plentiful and reactive. They formed water by reacting with all oxygen atoms, leaving no free oxygen. As a result, the primordial atmosphere was reducing (lacked free oxygen), as opposed to the current oxidizing environment (with free oxygen). Hydrogen atoms are mixed with nitrogen to make ammonia. (NH3). As a result, water and ammonia were most likely the first molecules on primaeval Earth.

Formation of Simple Organic Molecules (Monomers)

Simple organic molecules such as simple sugars (glucose, ribose, deoxyribose, etc.), nitrogenous bases (purines and pyrimidines), amino acids, glycerol, and fatty acids were formed as a result of early inorganic molecules interacting. When it rained, the water disintegrated and transported salts and minerals with it, eventually accumulating in the shape of oceans. As a result, the ancient oceans included a considerable quantity of dissolved NH3, CH4 nitrides, carbides, and other gases and elements. Solar radiations such as UV light and X-rays, energy from electrical discharges such as lightning, high energy radiations, or energy from unstable isotopes on the early Earth all provide the energy needed for such a chemical reaction.

The atmosphere lacked an ozone layer. Prebiotic Soup or Hot Dilute Soup is a soup-like broth of chemicals that developed in the waters of early Earth and is thought to be the beginning of living cells. The stage was now set with a mix of diverse chemical ingredients. Because the breakdown of organic molecules was prolonged without any life or enzyme catalysts, they were collected in the water. The lack of oxygen during this period also kept the synthesized organic molecules from being oxidized and degraded into more minor compounds.

Formation of Complex Organic Molecules (Macromolecules)

In the ancient oceans, a variety of amino acids, simple sugars, purines and pyrimidine bases, fatty acids, hydrocarbons, and other organic molecules were collected. Solar energy, electrical discharge, illumination, ATP, and polyphosphates might have given energy to organic synthesis polymerization processes. S.W. Fox demonstrated that heating a dry mixture of amino acids produces polypeptide molecules. Polypeptides can be combined to form various proteins. Similarly, simple sugars may be turned into polysaccharides, and fatty acids can be transformed into lipids. Finally, sugars, nitrogenous bases, and phosphates united to form nucleotides in the ancient oceans, which polymerized into nucleic acids.

Organic Molecules or Prebiotic Molecules

The fossilized evidence of photosynthetic bacteria suggests that forming primordial cells from macromolecules took half a billion years. Prebionts (non-living aggregates) containing carbohydrates, proteins, lipids, and nucleic acids are thought to have formed (coacervates droplets surrounded by a layer of water). Coacervates can selectively absorb water molecules. They can divide and multiply. Coacervates could perform rudimentary metabolic tasks such as starch synthesis and hydrolysis.

Coacervates represent the dividing line between non-living and living things. Early prebiotic cell forms, according to Oparin, were proteinoid microspheres. They had two layers. Organic macromolecules were trapped in the outer membrane. The microsphere functions similarly to a primordial cell. Some proteinoid molecules (protein-like entities consisting of branched-chain amino acids) performed enzyme activities. By bidding, they were able to create miniature microspheres.

Another theory is that Protobionts, abiotically formed entities with rudimentary lipid bilayer membranes, develop. Liposomes are another name for protobionts. Liposomes can develop in water when lipids and organic macromolecules are present. Liposomes' outer membranes can give rise to mini liposomes, and metabolic events can occur depending on the organic compounds present. The theories stated above are hypothetical. They might be an essential structure because forming a protocell necessitates separating complicated organic components from a watery boiling soup. These simulations might be a significant step towards the genesis of life.


The genesis of life on Earth is linked to the origin of the cosmos and the Oparin-Haldane Theory of the Origin of Life, which proposes that life on Earth arose spontaneously from non-living elements in response to ever-changing environmental circumstances. The early Earth was abundant in atoms such as hydrogen, oxygen, carbon, nitrogen, sulfur, and phosphorus, which formed inorganic molecules and simple organic molecules.

Prebiotic Soup is a soup-like broth of chemicals that developed in the waters of early Earth and is the beginning of living cells. The formation of Complex Organic Molecules (Macromolecules) took half a billion years in the ancient oceans, with solar energy, electrical discharge, illumination, ATP, and polyphosphates providing energy. Prebionts (non-living aggregates) containing carbohydrates, proteins, lipids, and nucleic acids are thought to have formed.

Updated on: 20-Apr-2023


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