A short article about Prof. Ahmed joining CSUF:
From left to right: Danielle Posey, Corbyn Jones, and Prof. Ahmed (Image courtesy of Shovit Bhari)
The SLAMLab welcomes two new members to our interdisciplinary research team. Looking forward to working together to study biophysics!
Danielle Posey – Senior majoring in Biology
Corbyn Jones – Sophomore majoring in Physics and Mechanical Engineering
We all had a great time at the new faculty dinner at President Garcia’s house! Thanks for the warm welcome. Below is an image of the new faculty joining the College of Natural Sciences and Mathematics as well as our new Dean, Marie Johnson, joining us from West Point. (photo courtesy of Matt Gush, University Photographer)
Nonequilibrium dissipation in living oocytes
Étienne Fodor*, Wylie W. Ahmed*, Maria Almonacid*, Matthias Bussonnier, Nir S. Gov, Marie-Hélène Verlhac, Timo Betz, Paolo Visco, Frédéric van Wijland
Living organisms are inherently out-of-equilibrium systems. We employ new developments in stochastic energetics and rely on a minimal microscopic model to predict the amount of mechanical energy dissipated by such dynamics. Our model includes complex rheological effects and nonequilibrium stochastic forces. By performing active microrheology and tracking micron-sized vesicles in the cytoplasm of living oocytes, we provide unprecedented measurements of the spectrum of dissipated energy. We show that our model is fully consistent with the experimental data, and we use it to offer predictions for the injection and dissipation energy scales involved in active fluctuations.
Available at http://arxiv.org/abs/1510.08299
Active mechanics reveal molecular-scale force kinetics in living oocytes
Authors: Wylie W. Ahmed*, Etienne Fodor*, Maria Almonacid*, Matthias Bussonnier, Marie-Helene Verlhac, Nir S. Gov, Paolo Visco, Frederic van Wijland, Timo Betz
Abstract: Unlike traditional materials, living cells actively generate forces at the molecular scale that change their structure and mechanical properties. This nonequilibrium activity is essential for cellular function, and drives processes such as cell division. Single molecule studies have uncovered the detailed force kinetics of isolated motor proteins in-vitro, however their behavior in-vivo has been elusive due to the complex environment inside the cell. Here, we quantify active force generation in living oocytes using in-vivo optical trapping and laser interferometry of endogenous vesicles. We integrate an experimental and theoretical framework to connect mesoscopic measurements of nonequilibrium properties to the underlying molecular-scale force kinetics. Our results show that force generation by myosin-V drives the cytoplasmic-skeleton out-of-equilibrium (at frequencies below 300 Hz) and actively softens the environment. In vivo myosin-V activity generates a force of F∼0.4 pN, with a power-stroke of length Δx∼20 nm and duration τ∼300 μs, that drives vesicle motion at v∼320 nm/s. This framework is widely applicable to quantify nonequilibrium properties of living cells and other soft active materials.
Check out our educational materials about how “Cells mix things up by actively stirring their insides” on Science Magazine’s educational website:
Check out our new review paper on Active Cell Mechanics!
Living cells are active mechanical systems that are able to generate forces. Their structure and shape are primarily determined by biopolymer filaments and molecular motors that form the cytoskeleton. Active force generation requires constant consumption of energy to maintain the nonequilibrium activity to drive organization and transport processes necessary for their function. To understand this activity it is necessary to develop new approaches to probe the underlying physical processes. Active cell mechanics incorporates active molecular-scale force generation into the traditional framework of mechanics of materials. This review highlights recent experimental and theoretical developments towards understanding active cell mechanics. We focus primarily on intracellular mechanical measurements and theoretical advances utilizing the Langevin framework. These developing approaches allow a quantitative understanding of nonequilibrium mechanical activity in living cells.