The Underlying Chemical Nature of Life
All known life depends on molecular interactions of a small number of different polymers. The two main groups are polynucleotides, such as DNA and various types of RNA, and polypeptides that comprise most of the catalysts controlling the rates of various biochemical reactions essential to maintaining life. DNA is the site of storage of the genetic information, coded as sequences of a small number of nucleotide monomers attached to one another in particular orders. DNA is transcribed in cells to messenger RNA which then serves as a template for manufacture of proteins, mediated by a small RNA molecule known as transfer RNA. The proteins can then modulate a large variety of metabolic reactions to release energy and to direct the synthesis of important cell components. These complicated interactions highlight the complexity of even the simplest forms of extant life. Presumably the emergence of life from a non living prebiotic "soup" of potential biomolecules must have had some kind of simpler, but no longer present form. Phylogenetic trees showing the relatedness of various organisms can be constructed using sequences of nucleotides found in certain vital RNA molecules common to all living forms. Such trees clearly demonstrate the close relationship of macroscopic multicellular organisms like plants and animals, especially compared to the much more distant relationships not only between them and simpler forms such as bacteria, but even between different groups of bacteria. It is clear that the common ancestor of all living forms was at least superficially similar to some kind of bacterium, but also that the first "living entity" most likely was even simpler in makeup. The transition from a prebiotic soup to life is a critical, but mostly hidden step in the history of life.