Origin of Life: Oparin-Haldane & Miller-Urey

Origin of Life Hypotheses

The Oparin-Haldane hypothesis suggests that life arose gradually from inorganic molecules, with "building blocks" like amino acids forming first and then combining to make complex polymers.

The primitive atmosphere was reducing, containing water vapor and ammonia.

Both Oparin and Haldane proposed that the first life forms were heterotrophs.

Oparin's Work with Coacervates

Oparin's work with coacervates confirmed that enzymes fundamental for the biochemical reactions of metabolism functioned more efficiently when contained within membrane-bound spheres than when free in an aqueous solution.

Haldane's Primordial Soup Idea

Haldane's ideas about the origin of life were very similar to Oparin's. Haldane proposed that the primordial sea served as a vast chemical laboratory powered by solar energy. The atmosphere was oxygen-free, and the combination of carbon dioxide, ammonia, and ultraviolet radiation gave rise to a host of organic compounds. The sea became a 'hot dilute soup' containing large populations of organic monomers and polymers. Haldane envisaged that groups of monomers and polymers acquired lipid membranes, and that further developments eventually led to the first living cells.

The Miller-Urey Experiment

The Miller-Urey experiment provided the first evidence that organic molecules needed for life could be formed from inorganic components under simulated early Earth conditions.

Simulating Early Earth Conditions

The two scientists combined warm water with a mixture of four gases—water vapor, methane, ammonia, and molecular hydrogen—and pulsed the "atmosphere" with electrical discharges. The different components were meant to simulate the primitive ocean, the prebiotic atmosphere, and heat.

Experiment Results

One week later, Miller and Urey found that simple organic molecules, including amino acids, had formed under the simulated conditions of early Earth.

Dehydration Synthesis

Dehydration synthesis is the formation of larger molecules from smaller reactants, accompanied by the loss of a water molecule. Many reactions involving dehydration synthesis are associated with the formation of biological polymers where the addition of each monomer is accompanied by the elimination of one molecule of water.