17. To explain origin of life the first biomolecule generated under lab condition were
    (1) Amino acids (2) Nucleic acids
    (3) Carbohydrates (4) Lipids

The Challenge of Explaining Life’s Origins

The origin of life is one of the most profound questions in science. For much of human history, life’s beginnings were explained through mythology or divine creation. In the 20th century, scientists began to seek naturalistic explanations, proposing that life could have emerged from simple chemical reactions under the right conditions.

This process, known as abiogenesis, involves the gradual assembly of complex biological molecules from simple inorganic precursors. The challenge was to demonstrate that such a transformation was possible, and to identify which biomolecules could form spontaneously under prebiotic conditions.

The Miller-Urey Experiment: A Landmark in Origin-of-Life Research

In 1953, Stanley Miller, working under the supervision of Harold Urey at the University of Chicago, conducted a groundbreaking experiment that forever changed our understanding of life’s origins. Their goal was to simulate the conditions thought to exist on the early Earth, including its atmosphere, energy sources, and water.

Experimental Design

Miller and Urey constructed a closed glass apparatus that contained:

• Water (H₂O): To simulate the early oceans.

• Gases: Methane (CH₄), ammonia (NH₃), and hydrogen (H₂), which were believed to make up the early atmosphere.

• Energy Source: Electric sparks to mimic lightning.

The apparatus was designed to circulate water and gases, exposing them to electrical discharges. After several days, the solution inside the apparatus turned reddish-brown, signaling the formation of new compounds.

Results: The Synthesis of Amino Acids

Analysis of the solution revealed the presence of several amino acids—the building blocks of proteins. This was a monumental discovery: for the first time, scientists had demonstrated that complex organic molecules essential for life could form spontaneously from simple inorganic precursors under conditions resembling those of the early Earth.

Amino acids are not only the building blocks of proteins but also play critical roles in metabolism, signaling, and other biological processes. Their synthesis in the Miller-Urey experiment provided strong experimental support for the idea that life’s building blocks could arise naturally, without the need for living organisms.

Why Amino Acids Were the First Biomolecules Generated in the Lab

Among the four major classes of biomolecules, amino acids were the first to be synthesized in laboratory experiments designed to explain the origin of life. This is because:

• Relative Simplicity:

  • Amino acids are relatively simple molecules compared to nucleic acids and complex carbohydrates. Their synthesis from inorganic precursors is chemically plausible under prebiotic conditions.

• Chemical Stability:

  • Amino acids are stable and can persist in aqueous environments, making them likely candidates for early biomolecule formation.

• Versatility:

  • Amino acids can polymerize to form proteins, which are essential for the structure and function of all living cells.

• Experimental Feasibility:

  • The conditions required to synthesize amino acids from simple gases and water are achievable in the laboratory, as demonstrated by Miller and Urey.

The Role of Other Biomolecules in Origin-of-Life Research

While amino acids were the first biomolecules synthesized in the lab to explain the origin of life, other biomolecules are also critical to the story of life’s emergence:

• Nucleic Acids:

  • Nucleic acids (DNA and RNA) are the molecules of heredity, carrying genetic information. The RNA World hypothesis suggests that RNA may have been the first self-replicating molecule, predating DNA.

  • However, nucleic acids are more complex than amino acids, and their synthesis under prebiotic conditions is more challenging. While some progress has been made in synthesizing RNA components in the lab, amino acids were synthesized first and remain easier to produce under simulated early Earth conditions.

• Carbohydrates:

  • Carbohydrates, such as sugars, are important energy sources and structural components. Their synthesis under prebiotic conditions has been demonstrated, but it is more complex than amino acid synthesis.

• Lipids:

  • Lipids are essential for forming cell membranes, which separate living cells from their environment. The self-assembly of lipids into membranes is a key step in the origin of life, but lipid synthesis in the lab under prebiotic conditions is less straightforward than amino acid synthesis.

The Significance of the Miller-Urey Experiment

The Miller-Urey experiment is widely regarded as a landmark in origin-of-life research. It provided the first experimental evidence that the building blocks of life could form spontaneously from inorganic precursors under conditions resembling those of the early Earth. This discovery supported the hypothesis that life could have arisen through natural chemical processes, without the need for supernatural intervention.

The experiment also inspired a new field of research into prebiotic chemistry, with scientists around the world repeating and refining the experiment under different conditions. These studies have shown that a variety of organic molecules, including amino acids, can be synthesized under a range of simulated early Earth environments.

Modern Perspectives on the Origin of Life

While the Miller-Urey experiment focused on amino acids, modern research has expanded to investigate the synthesis of other biomolecules, such as nucleic acids and lipids, under prebiotic conditions. The RNA World hypothesis, which posits that RNA was the first genetic molecule, is now a leading theory in origin-of-life research. However, amino acids remain central to the story, as they are essential for the formation of proteins and the development of metabolic pathways.

Recent advances in synthetic biology and molecular evolution have enabled scientists to engineer RNA enzymes (ribozymes) that can replicate themselves, recapitulating a key step in the origin of life. Nevertheless, the synthesis of amino acids under simulated early Earth conditions remains a foundational achievement in the field.

Key Takeaways

• Amino acids were the first biomolecules generated under laboratory conditions to explain the origin of life, as demonstrated by the Miller-Urey experiment.

• The Miller-Urey experiment showed that amino acids could form spontaneously from simple inorganic precursors under conditions resembling the early Earth.

• Amino acids are the building blocks of proteins, which are essential for the structure and function of all living cells.

• While nucleic acids, carbohydrates, and lipids are also critical to life’s origins, amino acids were synthesized first and remain easier to produce under prebiotic conditions.

• The correct answer to the question is:

  (1) Amino acids

Summary Table

Conclusion

Amino acids were the first biomolecules generated under laboratory conditions to explain the origin of life, thanks to the pioneering work of Stanley Miller and Harold Urey. Their experiment demonstrated that the building blocks of life could form spontaneously from simple inorganic precursors, providing strong support for the idea that life arose through natural chemical processes. While other biomolecules, such as nucleic acids, carbohydrates, and lipids, are also essential to life, amino acids remain the cornerstone of origin-of-life research.

In summary, the correct answer is:

(1) Amino acids