ABSTRACT
Most biological functions arise from molecular interactions rather than individual molecules. These interactions are often highly specific; that is, they are molecular recognition processes. In the course of natural evolution, biological functionality is expanded by the generation of new and specific molecular interactions (through gene duplication and differentiation), especially those between proteins and other macromolecules. Subversion or deception of native molecular recognition in a biological system through mimicry is the modus operandi of most, if not all, bioactive substances, including pharmaceuticals. In the past, most drugs were discovered serendipitously when they happened to be able to bind a receptor tightly and cause a desirable phenotypic change in a cell or organism. The advent of RNA aptamers made it possible to create ligands for intended targets in a more efficient way (Ellington and Szostak 1990; Tuerk and Gold 1990). Like small organic molecules, they are able to rapidly and tightly bind specific protein domains or a specific site on a domain in living cells or organisms. Like antibodies, they can be made to order specifically for a predetermined target.
