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Undergraduate and Graduate Studies

Physics Colloquium: Omar Saleh (UCSB)

April 17, 2015 - 5:30pm
Title: The elastic response of charged biopolymers
Abstract: The elastic response of a single polymer can explain certain material properties, including the thickness of polymer brushes and the mechanics of gels; in turn, these material properties have a variety of biological analogies, such as to the brush-like pericellular matrix surrounding certain cells. More fundamentally, the force-extension relation of a polymer can be predicted theoretically, making it possible to probe the structure of a polymer by measuring its elastic response. This works in a manner similar to scattering: just as scattering at a wave vector q gives information on structure at a length scale 1/q, the elastic response under applied tension f gives information on structure at a length scale x ~ kT/f. Thus, in exact analogy to low-angle scattering, low-force elastic measurements are needed to probe the interesting long-range structure of polymers. I will discuss the basic physics of low-force elasticity, and present our experiments on various polymers that validate the power of low-force elastic measurements. I will then focus on the role of electrostatics in modulating the elasticity of charged biopolymers, including single-stranded nucleic acids and hyaluronic acid. This data indicates a need to move beyond classic models of polymer physics (e.g. worm-like chain models); I will discuss progress in formulating such models.

Brief bio:

Omar Saleh received a B.S. in Physics from M.I.T. in 1997, then attended Princeton University for his graduate studies. For his thesis, he worked with Lydia Sohn to develop novel biosensors based on methods of micro- and nano-fabrication. He received his Ph.D. from the physics department in 2003, and then moved into the field of single-molecule biophysics. His post-doctoral research focused on magnetic-tweezer studies of motor protein dynamics, and took place at the École Normale Supérieure in Paris, France, with Vincent Croquette, David Bensimon and Jean-Francois Allemand. He arrived at UCSB in September 2005, where he is currently an associate professor in the Materials Department and director of the Biomolecular Science and Engineering (BMSE) Program. His lab studies the mechanical properties of soft and biological systems, with special focus on charged biopolymers; DNA/protein interactions; and self-assembled DNA systems. 


Every Friday 10:45-11:45 a.m., COB 267 (except as noted). Tea and cookies will be served from 10:30 - 10:45 a.m. Questions regarding the seminar series should be directed to Prof. Chih-Chun Chien