Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session X4: Functional Gels |
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Sponsoring Units: DPOLY Chair: Igal Szleifer, Northwestern University Room: Ballroom A4 |
Thursday, March 24, 2011 2:30PM - 3:06PM |
X4.00001: Micromechanical study of mitotic chromosome structure Invited Speaker: Our group has developed micromanipulation techniques for study of the highly compacted mitotic form of chromosome found in eukaryote cells during cell division. Each metaphase chromosome contains two duplicate centimeter-long DNA molecules, folded up by proteins into cylindrical structures several microns in length. Native chromosomes display linear and reversible stretching behavior over a wide range of extensions (up to 5x native length for amphibian chromosomes), described by a Young modulus of about 300 Pa. Studies using DNA-cutting and protein-cutting enzymes have revealed that metaphase chromosomes behave as a network of chromatin fibers held together by protein-based isolated crosslinks. Our results are not consistent with the more classical model of loops of chromatin attached to a protein-based structural organizer or ``scaffold". In short, our experiments indicate that metaphase chromosomes can be considered to be ``gels" of chromatin; the stretching modulus of a whole chromosome is consistent with stretching of the chromatin fibers contained within it. Experiments using topoisomerases suggest that topological constraints may play an appreciable role in confining chromatin in the metaphase chromosome. Finally, recent experiments on human chromosomes will be reviewed, including results of experiments where chromosome-folding proteins are specifically depleted using siRNA methods. [Preview Abstract] |
Thursday, March 24, 2011 3:06PM - 3:42PM |
X4.00002: A Molecular View of Liquid Crystalline Elastomers and Gels Invited Speaker: A combination of Monte Carlo and molecular dynamics simulations is used to examine the order-disorder transitions that arise in model liquid crystalline elastomers and colloidal gels as a function of concentration and strain, respectively. Two models are considered. In the first, a lattice model is used to represent a colloidal gel of nematogens and nanoparticles. In the second, a cross-linked elastomer of Gay-Berne mesogens is adopted to examine the order-disroder transition that arises as a function of strain. The results of simulations are compared to those of recent experiments for these two classes of systems. [Preview Abstract] |
Thursday, March 24, 2011 3:42PM - 4:18PM |
X4.00003: Gelation of mucin: Protecting the stomach from autodigestion Invited Speaker: In this talk I will describe the molecular mechanisms involved in the remarkable ability of the mucus lining of the stomach for protecting the stomach from being digested by the acidic gastric juices that it secretes. These physical properties can be attributed to the presence of a high molecular weight glycoprotein found in mucus, called mucin. Rheology and other measurements show that gastric mucin forms a gel under acidic pH. A model of gelation based on the interplay of hydrophobic and electrostatic interactions will be discussed. Molecular Dynamics simulation studies of folding and aggregation of mucin domains provide further support for this model. The relevance of gelation to the motion of the ulcer causing bacterium H. pylori will be discussed. [Preview Abstract] |
Thursday, March 24, 2011 4:18PM - 4:54PM |
X4.00004: Responsive gels and membranes Invited Speaker: We use computer simulations and analytical method to explore and analyze effects of composition heterogeneities in elastic membranes and gels. In particular, we focus on shape pattern formation in thin networks and elastic closed membranes driven by the presence of composition heterogeneities. We study the crumpling of multicomponent elastic membranes in response to changes in external conditions, as well as the spontaneous buckling transition of heterogeneous elastic shells into regular and irregular polyhedra. [Preview Abstract] |
Thursday, March 24, 2011 4:54PM - 5:30PM |
X4.00005: ABSTRACT WITHDRAWN |
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