Single molecule interactions in biological systems
The interactions of biological molecules are traditionally investigated using ensemble techniques. These provide information on the molecular behaviour based on averaged data resulting from collective ensemble properties. While this has enabled the resolution of structure and function of many proteins and other biomolecules, an understanding of how and why the molecules go about structural changes and modulate inter- and intra-molecular interactions is difficult to gain using these approaches. More recently, single molecule techniques have evolved. These allow us to follow the behaviour of the individual molecules over time and/or under changing conditions. From such data, subtle molecular changes can be resolved without the need to synchronise the system. Further, variations within a biological system can be detected which would be lost using the ensemble techniques, due to the concomitant averaging procedures. This is exploited to help understand the molecular procedures involved. In this thesis, the application and comparison of two of the main single molecule techniques, optical tweezers and AFM, are described. With these, a range of systems was investigated; namely drug-DNA, protein-DNA, and cell adhesive interactions. The presented results provide new and complementary information on the different biological systems, demonstrating the diversity of single molecule applications. The combination of different experimental approaches was further exploited to gain a more complete picture of the observed processes.