On the structural response of eukaryotic cells

textThe actin, microtubule and intermediate filament cytoskeletal polymer assemblies, along with their accessory proteins, govern the mechanical or structural response of an eukaryotic cell to an external stress. Using statistical mechanics tools, this dissertation investigates the molecular properties, such as mesh size, persistence length and filament length, that determine the structural strength of the in vivo polymer networks, with an emphasis on the actin network or the cortex of cells. Our study of actin shows how the wide range of shear moduli from 1 Pa to 1 kPa that spans the viscous sol-like state to the elastic gel-like state witnessed in eukaryotic cells can be achieved through transient crosslinking and the spatial distribution of actin and actin crosslinking proteins alone. Thus, this gel-sol transition is achieved without the action of any severing or capping proteins that depolymerize the actin network. In order to understand how the microscopic quantities controlling the structural properties of these in vivo polymers are related to the deformation of a cell observed experimentally, a cell model is created by us. It starts with modeling the actin cortex as a thick shell and increases in complexity to include microtubules and the nucleus. Our cell model predicts that the structural response of the cell amplifies changes in molecular properties such as the in vivo actin concentration. Hence, the sensitivity of the structural response to cytoskeletal changes can be used to distinguish between different cells such as normal and cancer cells and can serve as an indicator of disease.Physic