In this essay, we aim to draw a short comparison between 2 important research topics - circular and circulating RNAs - and show how they are connected. The findings described here in the field of circular RNAs, which are still quite obscured by the rapidly expanding body of knowledge in biology, have added another dimension to our view of the process of gene expression, which is formed by a more complex network of molecule interactions than we previously thought. The term "circulating RNAs" refers to a broad spectrum of RNA fragments originating from different sources, such as physiologically dying cells, sites of inflammation or cancer cells, and fragments floating in human liquid tissues together with other elements. Fragments of nucleic acids circulating in blood are emerging as promising biomarkers in different medical conditions. Interestingly, circular RNAs have been found to be present in human blood and form a fraction of circulating RNAs. In addition to updating readers on these fast-developing areas of biology, we also stress the need for the study of complex networks of molecule interactions as whole structures (in unison with the thoughts of systems biology), as opposed to the trend toward searching for individual key player molecules. Fundamentally, we want to add to the rationalization and synthesis of new research findings in the scientific literature, because this direction is important not only for students, teachers and researchers, but also for the general population.
Keywords: circular RNA; circulating RNA; complex networks; synthesis; systems biology.