History of development of the biological microworld

The history of modern biology may be considered to begin with the penetration of scientists to biological mini-world, formed by microorganisms, cells and sub-cellular entities. The main problem to be solved was the nature of biological (genetic) heredity. In the middle of the 19th century a conception was put forward about presence in living organisms of hereditary factors, later referred as genes, whose nature for a long period remained unknown. A significant progress was achieved with elaboration of the chromosomal theory of heredity based on the presence in cell nuclei of sub-cellular structures – chromosomes. In further search of hereditary agents the plausible candidate seemed to be a polymer chemically identified as deoxyribonucleic acid (DNA). But no fantasy was enough to establish any connection of DNA with phenotypical features of living organisms. In 1953 James Watson and Francis Crick in the process of construction of space model of DNA molecule succeeded to reveal a mechanism of copying non-regular sequences of four heterocyclic bases present as one per monomer in DNA. It was suggested that these sequences might be recognized as a hereditary information. But the real essence of heredity happens to be found not so in copying as in coding. This revolutionary idea was soon (in 1954) put forward by a physicist George Gamow who suggested that a sequence of bases in DNA is a genetic text and that living cells possess a genetic code which in fact is a mechanism of transformation of sequences of triplets of DNA monomers (the “letters” of genetic text) to amino acid sequences of a multitude of various proteins which are the main functional molecules of the living nature. Now a plenty of genetic texts were elucidated which made it possible for researchers to achieve a new level of knowledge about living nature.