A Molecular Structural Mechanics Model For The Mechanical Properties Of Microtubules

The cell is a functional unit of an organism,whose mechanical behavior affects the physiological activities of the living body.The cytoskeleton largely determines the mechanical properties of the cell.Microtubules are one of the important components of the cytoskeleton,which can maintain cell morphology,transport organelles and participate in cell mitosis.Microtubules play an important role in many physiological activities of the organism.Therefore,studying the mechanical properties of microtubules will promote understanding of cellular physiological processes.At the present,the numerical simulation methods for studying the mechanical properties of microtubules mainly include molecular dynamics simulation and molecular structural mechanics models.However,molecular dynamics simulations have limitations on spatial scales and time scales.The molecular structural mechanics model cannot be used to study large deformations of microtubules.Therefore,a nonlinear molecular structural mechanical model has been established for microtubules in the thesis.The mechanical properties of complete microtubules and microtubules with defects have been studied.The structural unit constituting the microtubules is the tubulin.Therefore the mechanical properties of the microtubules depend on tubulin itself and the interaction between two tubulins.In this thesis,the mechanical properties of a single tubulin have been explored by steered molecular dynamics simulation.The elastic coefficient of a single tubulin has been obtained.At the same time,molecular dynamics simulations have been used to explore the four different tubulin interaction structures in microtubules.The relationship between the interaction forces and tubulin distances has been obtained for four different structures.Based on the results of molecular dynamics simulation of tubulin,the nonlinear molecular structural mechanics model of microtubules has been established,in which elastic non-linear tension springs and linear elastic torsion springs have been used to simulate the interaction between two tubulins using finite element method.The elastic modulus of the complete microtubules under uniaxial tensile load has been investigated to verified the reliability of the model.The fracture process of the complete microtubules has been analyzed.Based on the nonlinear molecular structural mechanics model,the microtubules missing different numbers of tubulin have been uniaxially stretched.The corresponding stress-strain relationships have been obtained.The mechanical properties of microtubules with defects have been studied,that is the effects of tubulin missing on elastic modulus of microtubules and ultimate strain.Result show that the elastic modulus and ultimate strain of microtubules both decrease linearly with the increase of tubulin deletion rate.