[Complexity of the phenomenon of life - the challenge for medicine].

The human organism presents a complex biological system that has hierarchical organization. The lowest, basal hierarchical level is composed of chemical molecules. The system's structure as "the whole" is maintained by complex interactions of its parts (molecules). New forms and functions, not present in molecules themselves emerge from their orchestrated and coordinated interaction, creating the novel "whole". The "whole" is not a simple summation of its parts. Therefore, on the basis of reductionist analysis and solely on the list of component elements of biological systems it is not possible to predict the future form and function of the "whole". The information included in genes is not directly or proportionally expressed as the phenotype. The phenotype is based on secondary information and arises from the complex interaction of component elements of the system. On a basal (molecular) level, biological systems function according to self-organization rules. No central regulatory device is providing instruction for molecular interaction. Regulatory centers that coordinate the system are dispersed all over the system from molecular level up, keeping it in order and preventing a system to enter the chaos space. Advances in biology and development of new research technologies, as well as bioinformatics, computer sciences and mathematical modeling have enabled research on interaction of cellular macromolecules (proteins, DNA, RNA, etc.) that in a living cell are organized into large dynamic network. Some rules of a structural and functional networks' properties, as well as their organization were discovered. The above research area is regarded as a new academic field termed systems biology. Based on systems biology, many new concepts in medicine, particularly the mechanisms of biogenesis and development of diseases have emerged have potential application for early diagnostics and therapy.