PHYLOGENY 



an artificial atmosphere in a sealed flask, Miller obtained a mixture of 

 many amino acids and other organic compounds, some in fairly high 

 yields. 



Further reactions of the compounds discussed above have great poten- 

 tialities. The hydrocarbons are not particularly reactive; however, one 

 hydrogen atom in a hydrocarbon molecule could be readily replaced by 

 chlorine or bromine. The new compound would be highly reactive. It 

 might, for example, be hydrolyzed to form an alcohol and an inorganic 

 acid. The alcohol could then be oxidized to form the corresponding alde- 

 hvde or ketone. These could, in turn, be further oxidized to form organic 

 acids. The simplest of the aldehydes, formaldeh)'de, is an intermediate 

 compound in the photosvnthetic production of sugar. The reaction to pro- 

 duce glucose (CgHioOo) from formaldehvde (CH2O) proceeds extremelv 

 slowly in the absence of chlorophyll and sunlight. But it does proceed, 

 however slowly, under the influence of sunlight alone, and, given time on 

 a geologic scale, it is quite conceivable that large quantities of sugar might 

 be accumulated. If a double alcohol, or glycol, were formed, then one 

 alcohol group could be oxidized to form an acid, while the other alcohol 

 group could react with ammonia (NH3) to give water and an amine. The 

 result would be an amino acid, one of the building blocks of the proteins. 

 The simplest possible amino acid is glycine, CH:.'NHi..'COOH. 



These compounds can enter into reactions which lead to compounds 

 intimately associated with protoplasm. Sugars can be polymerized to form 

 starches, glycogen, and cellulose. The essential precursors of fats are long- 

 chain hvdrocarbons in which an end member has been oxidized to form 

 an acid, and glycerine. Glycerine is simply a three-carbon chain in which 

 one hydrogen on each carbon has been replaced by an hydroxyl group 

 ( CHoOH-CHOH-CHoOH ) . Now if each hydroxyl group reacts with a 

 long-chain organic acid, the resulting compound is a fat molecule. But the 

 most significant possibility is held by the amino acids, for these can react 

 with one another to form aggregates of great molecular weight, the pro- 

 teins. The acid group of one amino acid reacts with the amino group of 

 another in what amounts to a salt-forming reaction. This is called the 

 peptide linkage. As it always leaves an acid radical exposed on one of the 

 reacting amino acids and an amino group on the other, the reaction is 

 subject to indefinite repetition, and thus loads to the great molecular 

 weights of the proteins. 



Colloids, Coacervotes, and Individuality. By the time the earth had 

 cooled sufficiently to permit the formation of permanent bodies of water, 

 there was probably a large amount of organic jnaterial of great variety, 

 and the varietv was continualK' increasing through the natural experiment 

 of reaction between whatev(>r substances could react and happcMied to be 

 brought together. Many of these large organic compounds would tend to 

 form colloidal solutions in water. Wherever such colloidal particles in- 

 clud(Kl electrically active groups, as all proteins do in abundance, water 

 molecules would tend to become oriented around the surface of such a 

 particle. If colloidal droplets of opposite^ electrical charges should be 

 mixed, then they would be mutually precipitated to form droplets of a 



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