4 - 20190928 - Wat doe ik nou eigenlijk?

Op verzoek een korte uitleg over wat ik doe voor een opdracht.

Biological membranes consist of a combination of lipids, proteins and sterols. Fundamentally, a membrane is constructed of a phospholipid bilayer, which forms a stable barrier between the inside and the outside of the cell. The proteins carry out different functions, like molecular transport or cell-cell recognition. The sterols, mostly consisting of cholesterol, help structure the membrane and supports in raft formation.

In Figure 1 schematic representation of a bilayer is presented. The outside of the membrane, the outer leaflet, is formed predominantly by phosphatidylcholine (PC), sphingomyelin (SM) and glycolipids. The inside of the membrane, the inner leaflet, contains mostly phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). Cholesterol (Chol) is distributed equally between the bilayers.

Figure 1

The first important function of the bilayer membrane is being the barrier between the in- and outside of the cell. It is important to note that the naturally occurring phospholipids are in fact not solid, but a very viscous fluid. This introduces the second important function, the transport of molecules through the viscous membrane. The molecular transport, as well as different membrane functions, are carried out by proteins, not the lipids. In Figure 2 a schematics representation is portrayed how proteins are organized inside the membrane bilayer.

Figure 2

Cholesterol makes up a large portion of a membrane. By itself it does not form a membrane, but its rigid multiring structure is plays a critical role in membrane structures. The influence cholesterol has on the apparent lipids changes with changing temperature. In turn this influences the fluidity of the membrane. At low temperatures cholesterol interferes  with interactions between fatty acid chains and prevents freezing. At high temperatures the effect turns around and interferes with the fatty acid chains, making the outer leaflet less fluid and reducing its permeability to small molecules.

Cholesterol also makes up a big portion of hypothesized “rafts”. A raft is a discrete domain which appears to be enriched in cholesterol and sphingomyelin. They are thought to move laterally over the plasma membrane and might exert specific membrane functions. When different types of analysis over membranes are conducted it appears that the liquid-crystalline disordered phase is not the only phase in which biological membranes are realized. Partially the membrane can be in a the liquid ordered phase or a phase with similar properties .

To analyze these phase behaviors and local compositions of the membrane multiple analysis techniques can be conducted, such as differential scanning calorimetry (DSC), solid state deuterium nuclear magnetic resonance (2H NMR) and fluorescence spectroscopy. During this project DSC and 2H NMR are applied. DSC is a convenient, powerful and non-intrusive thermodynamic technique to obtain information on the phase behavior of lipids in biological and model membranes. 2H NMR is a less convenient and more invasive method to obtain locational information of deuterium marked components.

Dit was van origine het plan. Ondertussen hebben ze er een synthese van PSM bij gedaan. Leuk om weer een chemische synthese te doen, maar is toch andere koek dan de syntheses die ik tijdens mijn eerste jaar chemie heb gedaan. De complete methode duurt 4 maanden. Mijn versie hebben ze ingekort, want vier maanden aan synthese is nogal lastig in twee maanden. De eerste stap zou in een dag moeten kunnen, ik was in twee dagen nog niet klaar. Dus ik hoop dat ze hem genoeg hebben ingekort, anders dan ben ik met de ingekorte versie alsnog vier maanden bezig.. Wie had gedacht dat ik nog eens een biochemicus zou worden!