Harvard University, Deparment of Chemistry and Chemical Biology
techniques offer a powerful approach to investigate complex physical
and biological processes. In this work, we present two topics in
polymer physics: polymer conformation hysteresis and characteristic
periodic motion in shear flow. In the first experiment, we directly
visualize long chain DNA molecules in planar extensional flow using
fluorescence microscopy and observe that the conformation of a single
polymer is strongly dependent on its deformation history.
Conformation hysteresis arises due to intramolecular hydrodynamic
interactions. In a separate experiment, we observe a characteristic
periodic motion for both free and surface-tethered DNA molecules in
shear flow, and we present scaling analyses for this behavior.
Experimental results are complemented by results from Brownian
dynamics simulation. We also study biological systems using single
molecule tools. In one research area, we study DNA replication by
direct observation of single DNA polymerase molecules on DNA strands
in vitro. A flow-stretched DNA assay allows for
characterization of enzymatic rate, processivity, and pausing during
DNA synthesis as a function of base pair content.