ABSTRACT
Intra- and intermolecular forces hold together biomolecular structures and mediate molecular interactions. Forces are also central in any kind of motion, such as the movement of motor proteins along tracks in muscle contraction, chromosome segregation or organelle transport, or the translocation of proteins along nucleic acids. Atomic force microscopy has been used to study the mechanical properties of nucleic acids, polypeptides, and polysaccharides, and to investigate the unfolding of proteins and DNA. The DNA in the bacterial nucleoid is associated with numerous proteins that mediate the compact folding of the DNA. The quadruple trap allows the application of force on bridged DNA molecules, and to interrogate their mechanical stability. Optical trapping and force measurements are also possible in vivo. The application spectrum of optical tweezers has been expanded by introducing torque and by combining optical tweezers experiments with fluorescence detection by total internal reflection fluorescence, confocal or wide-field microscopy, or fluorescence resonance energy transfer.
