Force Spectroscopy of DNA and RNA: Structure and Kinetics from Single-Molecule Experiments

Force spectroscopy of individual DNA and RNA molecules provides unique insights into the structure and mechanics of these for life so essential molecules. Observations of DNA and RNA molecules one at a time provide spatial, structural, and temporal information that is complementary to the information obtained by classical ensemble methods. Single-molecule force spectroscopy has been realized only within the last decades, and its success is crucially connected to the technological development that has allowed single-molecule resolution. This chapter provides an introduction to in vitro force spectroscopy of individual DNA and RNA molecules including the most commonly used techniques, the theory and methodology necessary for understanding the data, and the exciting results achieved. Three commonly used single-molecule methods are emphasized: optical tweezers, magnetic tweezers, and nanopore force spectroscopy. The theory of DNA stretch and twist under tension is described along with related experimental examples. New principles for extracting kinetic and thermodynamic information from nonequilibrium data are outlined, and further examples are given including the opening of DNA and RNA structures to reveal their energy landscape. Finally, future perspectives for force spectroscopy of DNA and RNA are offered.