Bulletin of the American Physical Society
Mid-Atlantic Section Fall Meeting 2020
Volume 65, Number 20
Friday–Sunday, December 4–6, 2020; Virtual
Session E01: Principles of Molecular and Cellular Biophysics: II |
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Chair: Eldon Emberly, Simon Fraser University |
Saturday, December 5, 2020 11:30AM - 12:06PM |
E01.00001: Organizing space at the cellular scale using molecular lawnmowers Invited Speaker: Eldon Emberly Nature utilizes molecular machines to organize space at the cellular scale. A number of these machines operate via a mechanism known as a burnt bridges Brownian ratchet (BBR), where the machine consumes energy to form a spatial gradient of a substrate that drives motion. These `lawnmowers' can be found in bacteria where they spatially segregate genetic material. Recent experimental work has shown that BBR systems can be designed and implemented in vitro to drive the motion of spherical particles along surfaces. In this talk I will present our modelling efforts to understand the complex dynamics of BBRs that have been observed both in vivo and in vitro. For in vivo BBRs I will show how cellular confinement and a competition for the substrate can aid the faithful spatial segregation of cargo. Lastly, for the spherical particle BBRs, I'll show how the chemical kinetics and elastic properties of the surface can be tuned to control the persistence and mode of motion, whether rolling or sliding. The varied dynamics of BBRs make them well suited to solve the vast assortment of transport problems that Nature provides. [Preview Abstract] |
Saturday, December 5, 2020 12:06PM - 12:42PM |
E01.00002: Designing the Morphology of Separated Phases in Multicomponent Liquid Mixtures Invited Speaker: Andrej Kosmrlj Phase separation of multicomponent liquid mixtures plays an integral part in many processes ranging from industry to cellular biology. While the physics of binary and ternary liquid mixtures is well-understood, the thermodynamic properties of $N$-component mixtures with $N>3$ have remained relatively unexplored. This makes it challenging to understand how cells control concentrations of molecules and their interactions to navigate phase diagrams to achieve target structures. To address this issue, we developed novel algorithms for constructing phase diagrams and for predicting the morphology of separated phases. To determine the number of coexisting phases and their compositions, we developed a new algorithm for constructing complete phase diagrams, based on numerical convexification of the discretized free energy landscape. Furthermore, we developed a graph theory approach to predict the topology of coexisting phases from a given set of surface energies (forward problem), enumerate all topologically distinct morphologies, and reverse engineer conditions for surface energies that produce the target morphology (inverse problem). [Preview Abstract] |
Saturday, December 5, 2020 12:42PM - 1:18PM |
E01.00003: Nonequilibrium energy transduction in stochastic strongly coupled rotary motors Invited Speaker: David Sivak Living systems at the molecular scale are composed of many constituents with strong and heterogeneous interactions, operating far from equilibrium, and subject to strong fluctuations. These conditions pose significant challenges to efficient, precise, and rapid free energy transduction, yet nature has evolved numerous biomolecular machines that do just this. What are the physical limits on such nonequilibrium performance, and what machine designs actually achieve these limits? In this talk, I discuss a simple model of the ingenious rotary machine that makes ATP (the predominant portable energy currency of the cell), where one can investigate the interplay between nonequilibrium driving forces, thermal fluctuations, and the strength of interactions between strongly coupled subsystems. This model reveals nontrivial yet intuitive design principles for effective molecular-scale free energy transduction. Most notably, while tight coupling between machine components is intuitively appealing, output power is in fact maximized at intermediate-strength coupling, which permits lubrication by stochastic fluctuations with only minimal slippage. [Preview Abstract] |
Saturday, December 5, 2020 1:18PM - 1:30PM |
E01.00004: Using a Modified, Safer Ames Test and Drosophila Melanogaster to Determine the Mutagenic Effects of Low-Frequency Radiation on Living Systems. Ryan Grzymala Cell phones and radar emit low-frequency radiation. This has driven some to question whether these items cause adverse effects such as cancer, given the amount of time people are exposed to them. Using Drosophila Melanogaster (DM) and an E. coli variation of the Ames test, the living systems were exposed to both cell phone and radar low-frequency radiation. Trial A results of cell phones and radar exposure were inconclusive due to the experimental controls. For the next four trials, several new controls were implemented including duration of exposure (1, 2, and 8 hours), an active cell phone call instead of the cell phone simply powered on, monitoring temperature and humidity more frequently, and changing the species of DM to one with all recessive traits. These new trials resulted in a 0{\%} mutation rate for all groups and all exposure times. Additionally, all populations of the tubes followed the same trend over the three generations, thus showing that exposure to both cell phone and radar low frequency radiation yielded no effect on the birthrate of DM. For the modified Ames test with E. coli, after exposure, the results showed a coloration that was defined as being non-toxic. In conclusion, both tests support the theory that cell phones and radar do not increase mutation rates. [Preview Abstract] |
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