Vejleder: John H. Ipsen
Over the last 20 years cell biology has undergone dramatic changes in understanding of basic processes in the biological cell like signaling, transport, pathogenic action and much more, which can be summarized in the collective designation The Raft Hypothesis. The basic picture in the the 'Raft' Hypothesis is that a wealth of biochemical and biophysical phenomena exploit the lateral heterogeneity of the biological membrane induced by cholesterol. However, behind this understanding is buried physical phenomena relying on co-operative properties of the lipid membrane, e.g. phase transition, phase separation, pseudo-critical fluctuations and mechanics. Furthermore, it involves a complex interplay between 1D, 2D and 3D physics.
This bachelor project takes the route from the characteristics of the lipid molecules involved to their self-assembly into complex quasi-2D buid bilayers with in-plane co-operative properties. The mechanism behind the main melting phase transition (solid-ordered (So) to liquid-disordered (Ld) phase transition) will be discussed with simple thermodynamic and statistical mechanical toy models. Furthermore, the role of cholesterol will be discussed in splitting translational and molecular degrees of freedoms resulting in a new bilayer phase (liquid-ordered (Lo)) which provides the bilayer with mechanical strength and makes it a strong permeability barrier. In addition, the phase coexistence between Lo and Ld phases provides a mechanism for lateral organization into domains with distinct physico-chemical properties. Today, it is generally accepted that physical properties of lipid bilayers with high cholesterol content was exploited by the biological evolution to forms of life based on cells defined by a plasma membrane, e.g. the animal kingdoms. The project will go through a variety of physical aspects of fluid domain formation in membranes, e.g. budding, monolayer registry, droplet fluctuations, small versus large domains, influence on membrane mechanics and anesthetic effect.