In 1953, Harold Urey and Stanley Miller carried out an amazing experiment in which they produced "molecules of life" from a mixture of gases that they proposed existed in a primordial earth. The experiments simulated what would happen when lightning strikes provided energy for chemical reactions in the atmosphere and suggested a hypothesis for how life might have developed on our planet. Amino acids were the vital molecules that formed in this experiment and supported this hypothesis for the origin of life.
An amino acid is a molecule that contains two functional groups, an amine and a
carboxylic acid , as shown in Figure 1. In this illustration there is an additional group called the side chain, designated with an R. The variation seen in naturally occurring amino acids arises from differences in this side chain. The twenty naturally occurring molecules are listed in Table 1. In an aqueous solution, this structure may change so that a proton from the COOH transfers to the NH2 and a zwitterion is formed. This structure depends on the pH of the solution. Most physiological systems fall into such a pH range so the zwitterion form of amino acids is the most stable form in the human body.
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Amino Acid
