Condensed Matter and Biological Physics Seminars

The standard diffraction limit of light is about 250 nm, meaning that you cannot "resolve" objects closer than this distance. Despite this, we have come up with a method to measure single molecules within 1.5 nm in 1-500 msec, using a technique we call Fluorescence Imaging with One Nanometer Accuracy (FIONA). We have chosen to study molecular motors, which are involved in moving things around within the cell, both in purified systems, and inside living cells. There has been a question as to whether molecular motors move things in an "inchworm" fashion, or in a "hand-over-hand" fashion (i.e. by "walking"). We have definitively determined that myosin, and kinesin, two important motors, walk in a" hand-over-hand" manner in purified systems. We have also made chimeras of myosin V and myosin VI, two motors which go in opposite directions, to help us figure out what determines the direction of movement. Finally, in living cells (that is, in Drosophila, or fruit fly cells), we have seen cargos being moved by individual "conventional" kinesin and dynein. We find that both kinesin and dynein move cargo 8 nm per ATP. Amazingly, these two molecular motors do not engage in a tug-of-war, but appear to be cooperative, taking turns hauling the cargo.