Miller–Urey experiment

The Miller - Urey experiment (including Urey -Miller experiment or Miller experiment) is used to confirm the hypothesis that under the conditions of a postulated primitive atmosphere a generation of organic molecules (chemical evolution), as they occur in living things today, is possible.

Stanley Miller simulated in 1953, together with Harold Clayton Urey in the laboratory of the University of Chicago a hypothetical early earth's atmosphere. The experiment he described in his publication: production of amino acids under possible conditions of a simple earth.

In the Miller - Urey experiment mixing simple chemical substances of a hypothetical early earth's atmosphere - water (H2O ), methane (CH4 ), ammonia (NH3 ), hydrogen ( H2) and carbon monoxide ( CO) - and sets this mix of electric discharges, which the power supply are designed to track by flashes of lightning. In this case, after a certain time arise organic molecules. The analysis of the resulting molecule, the mixture was carried out by chromatography.

Results

In an initial set of 59,000 micromoles of CH4 occur:

(* proteinogenic amino acids)

Overall, 18% of the methane molecules are converted into biomolecules from the rest creates a tar-like mass.

Originally performed in 1953, this experiment has since found similar results in many varieties. It is regarded as evidence that the early Earth's atmosphere contained organic molecules in non-negligible concentrations.

In 2008, studies carried out on the original vessels used by Miller led to the identification of a further eight, mostly hydroxylated amino acids that had been overlooked by the analysis of the 1950s. The experiment can, however, make any statements about how these molecules would have connected about to large structures.

Modifications of the experimental conditions

• As the carbon source: carbon monoxide ( CO) or carbon dioxide
• As a nitrogen source: molecular nitrogen N2
• As an energy source: UV light and fire as a heat source

What the Miller experiment alone does not explain

• The amino acids are formed as 1:1 mixtures of racemates, in the organisms but are mostly only the L- amino acids to be found. The problem is solved by minerals as catalysts, but have not been used by Miller.
• In addition to some amino acids are also formed compounds that do not occur in living organisms today, for example, the two isomeric amino acids to alanine β -alanine and sarcosine (see table). The absence of these compounds in today's organisms could possibly be explained by selection in the evolution of metabolic pathways, which all variants were eliminated except for the today used by organisms amino acids.

Pathways in the Miller experiment

First, there are from the starting materials aldehydes ( R -CHO) and hydrocyanic acid ( hydrogen cyanide HCN ) as the first intermediate products.

In a subsequent multi-stage reaction, the aldehydes react with amino acids to ammonia as the catalyst:

This results from the aldehyde methanal (HCHO ) the amino acid glycine, from ethanal ( CH 3 CHO ) is produced alanine.

From methanal glycolic acid ( α - hydroxyethanoic ), ethanal from the lactic acid ( α - hydroxy propanoic acid ) and propanal (CH3 - CH2 -CHO) produced the α -hydroxybutyric acid.