The Chemical Origins of Life
...G]http://www.science.siu.edu/microbiology/micr425/425Notes/Image126.gif[/IMG] Metabolism in Coacervates: Redox Reaction and Polymerization Source: http://www.science.siu.edu/microbiology/micr425/425Notes/14-OriginLife.html Liposomes have a lipid bilayer separating proteins from the environment and can easily be formed by simply dropping a small amount of oil in water. Liposomes can behave dynamically by engulfing smaller liposomes then splitting into two smaller liposomes. A coacervate is a liposome with enzymes in the lipid bilayer. RNA replication: Tom Cech (1980s) showed that rybozymes can edit introns from RNA. These short RNA polymers can copy RNA as a template (like clay). This establishs a form of heredity with no retention or biological evolution. However, autocatalytic short RNA began to fold into three dimensional structures. At this point the phenotype is the same as the genotype. RNA-amino acid interactions lead to proteins. Some of these proteins act as enzymes to help stabilize the RNA replication. [IMG]http://www-micro.msb.le.ac.uk/109/Origins4.gif[/IMG] The Catalytic Function of RNA Source: http://www-micro.msb.le.ac.uk/109/Origins.html The first step toward translation was the transferring of molecules held in proximity to the replicating RNA. The RNA configurations then led to positive selections. Synthesis of Purines: “Adenine is a pentamer of hydrogen cyanide. On the primitive earth a tetramer of HCN probably formed by successive condensations. This then rearranged under the influence of ultraviolet light to form one ring. A fifth HCN then condensed with this precursor to form the second ring. When HCN is heated in solution with NH3 a black tar is formed together with adenine as the major soluble aromatic product…. Smaller amounts of guanine and other purine derivatives are also formed…. Inorganic polyphosphates would have been present in primeval times (formed by volcanic heat from phosphates for example). Polyphosphates can react with many organic molecules to give organic phosphates. Amino acids give two possible products. Acyl phosphates have the phosphate group attached to the carboxyl group of the amino acid (NH2CHRCO-OPO3H2) Phosphoramidates have it attached to the amino group of the amino acid (H2O3P-NH-CHR-COOH). Heating or irradiation will then give polypeptides. Modern life uses acyl phosphate derivatives during protein synthesis. However, laboratory synthesis of DNA uses phosphoramidates. Analogous reactions can give AMP from adenine and polynucleotides can then form by polymerization. Biological information is passed on by template-spec...