The cell membrane is not a simple assembly of lipids and proteins. There are many internal degrees of freedom in a membrane, such as the shape of lipid molecules, the tilt direction of lipid molecules and the species of lipids and proteins in a biological membrane. Here we study two different internal degrees of freedom in membranes and their effects on the cell morphology and biological processes. Motivated by the propensity for tilt order and the common occurrence of narrow necks in the intermediate stages of biological processes such as endocytosis and vesicle trafficking, we examine how tilt order inhibits the formation of necks in the equilibrium shapes. In addition, motivated by recent experiments which showed that the mechanical properties of membranes play an important role in lipid sorting, a model is developed to study how the coupling between membrane composition and membrane bending stiffness and tension affects tubule formation in a multi-component membrane. We show that drawing a tubule from a vesicle leads to a rearrangement of composition in which the phase of higher flexibility segregates into the highly curved tubule. Lastly, this thesis will also study the synchronization of cilia and flagella. Motivated by the observed coordination of nearby beating cilia, we use a scale model experiment to show that hydrodynamic interactions can cause synchronization between rotating paddles driven at constant torque in a very viscous fluid. Synchronization is only observed when the shafts supporting the paddles have some flexibility. The phase difference in the synchronized state depends on the symmetry of the paddles. Calculations using the method of regularized stokeslets and analytic theory match the experimental observations well.
|Advisor:||Powers, Thomas R.|
|School Location:||United States -- Rhode Island|
|Source:||DAI-B 71/11, Dissertation Abstracts International|
|Subjects:||Mechanics, Mechanical engineering|
|Keywords:||Cell membranes, Degrees of freedom, Lipid sorting, Reynolds number, Synchronization|
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