Authors:	Jung, Maike
Title:	Modeling Membrane Dynamics on the Level of Organelles
Online publication date:	27-May-2021
Year of first publication:	2021
Language:	english
Abstract:	Biological membranes are omnipresent in cells, not only enclosing organelles but also in the form of highly dynamical structures such as tubular protrusions or complex branched networks. Investigating the dynamics of these membranes can be a challenging task in both experiments and computer simulations, because of the time and length scales that need to be accessed. In this work, conformational membrane changes are investigated by performing computer simulations using a dynamically- triangulated membrane model, which is based on a continuum description of the Helfrich Hamiltonian. This description is relatively general and allows to access larger length and time scales than in typical atomistic or coarse-grained simulations. In the first part of this thesis, the model is applied to study the formation of tubular structures from vesicles by pulling with an external force. Our findings are compared to theoretical approximations and minimal-energy solutions of the Helfrich Hamiltonian, exploiting the rotational symmetry of the structures. We find a very good agreement between the shapes found in theory and simulations. We also simulate the formation and coalescence of several tubes protruding from a vesicle. In the second part, we focus on the formation, energetics and stability of purely tubular and branched structures under the action of an external field and different global constraints. We find that both structures are unstable, when releasing the external force, which means that in nature other types of stabilization mechanisms must be present. We can show that when fixing the area to volume ratio of the structure, which is a natural constraint for closed impermeable membranes, tubes are metastable, while branches are still unstable. To stabilize these branches, an additional constraint therefore has to be set. One possibility which we successfully applied in this thesis is fixing the overall curvature of the system. These findings show that tubular networks observed in biological cells need to be stabilized by either anchoring to organelles or filaments, or by controlling the overall curvature through curvature-inducing proteins or an area difference between the two monolayers of the lipid bilayer. Computer simulations of biological membranes and in particular continuum models thus provide a very valuable and useful tool for interpreting and complementing experimental observations.
DDC:	500 Naturwissenschaften 500 Natural sciences and mathematics 530 Physik 530 Physics
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 08 Physik, Mathematik u. Informatik
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-5905
URN:	urn:nbn:de:hebis:77-openscience-70914c6c-47a5-45c3-b346-a572b3923cfa0
Version:	Original work
Publication type:	Dissertation
License:	CC BY-ND
Information on rights of use:	https://creativecommons.org/licenses/by-nd/4.0/
Extent:	7, iv, 140 Seiten, Illustrationen, Diagramme
Appears in collections:	JGU-Publikationen