Miller–Urey experiment Review of Stanley Miller Paper I. What was Stanley Miller’s hypothesis? Stanley miller hypothesized that the earth’s atmosphere had conditions that favored the formation of organic molecules from inorganic precursors such water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2).
II. What did the different parts of his system mimic
a) The water in the boiling flask; this may have represented the ocean. The heating may have been from volcanic activity providing constant supply of steam.
b) Spark; this represented lightening that was present to provide the necessary energy for the reactions to occur.
c) Condenser; represented the cool part of the atmosphere that allowed the condensation of the organic molecules.
d) The ‘ U’ tube represented the forward cycle of events, from vapor formation that prevented the reverse occurring. That is, decomposition of the organic molecules to give the inorganic molecules.
III. What molecules did he start with
Water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2)
IV. What molecules did he end up with
Amino acids (glycine, alanine and aspartic acid) and simple sugars (Barton, Briggs and Eisen)
V. a) Reason for turbidity- this was due to colloidal silica from the glass flask. It may also have been as a result of some organic substances dissolving into the water.
b) Reason for red colour-this was due to organic substances adsorbed on the silica.
VI. Addition of HgCl2- This prevented the growth of organisms (e. g. bacteria) in the mixture. HgCl2 is mercury (II) chloride, a compound of chlorine and mercury.
VII. Ampholytes-these are molecules that contain both acidic and basic properties. Also known as zwitter ions. Examples are some amino acids. The separation was so as to isolate the amino acids for characterization
VIII. Filtration was done to remove solid impurities such as the silica. The concentration was done to facilitate better results during chromatography and characterization. This is because a concentrated solution would respond better than a dilute solution with diffuse molecules.
IX. Paper chromatography is a method of separation and identification of compounds. It utilizes the principle of capillarity and also solubility (to facilitate separation). Colour is often used to allow the identification of compounds. The properties include; molecular weight, structure, shape of the molecule, and the polarity of the molecule.
X. He used two dimensional paper chromatography
XI. Ninhydrin is a chemical compound that reacts with amino acids (with certain exceptions such as proline) to produce a deep blue colour (Ruhemanns purple). This allows visibility of the amino acid
XII. He was able to tell the presence of the amino acids by the ninhydrin indicator. For their individual discrimination, he used comparison of spot size and colour to known templates of characterized amino acids.
XIII. Miller knew the total yield was in the milligram range by informed inference. Knowing that the system was closed, the total mass of reagents remained the same (gases included). By weighing the remaining fractions in the flask, and subtracting impurities by silica, he may have obtained a rough idea of the amount. That is; total mass of reagents (minus apparatus) = Amino acids mass + remaining reagents(minus impurities). It though may not be entirely accurate, as the amino acids existed in aqueous state, thus requiring the factoring in of water of dissolution.
XIV. Miller’s conclusions were that it was actually possible to manufacture organic molecules from inorganic precursors under optimum conditions. These were such as the amino-acids.
XV. His experiments did test his hypothesis. Though not accurate in the reproduction of the original setting of primitive earth, they showed that indeed it was possible that the primitive atmosphere contained the right inorganic molecules, the right conditions and the right amount of energy to produce organic molecules.
XVI. A good experiment to do next would be one on synthesis of nucleotides. If amino acids could be produced, then similarly, nucleotides might also have been produced, sparking the beginning of biological life.
References
Barton, Nicholas H.; Briggs, Derek E. G.; Eisen, Jonathan A.; Goldstein, David B.; Patel, Nipam H. (2007), Evolution, Cold Spring Harbor Laboratory Press, p. 93-95
