Neutron Reflectivity investigation of the structure of a phospholipid bilayer membrane using the Advanced Neutron Diffractometer / Reflectometer (AND/R)

Phospholipid bilayer are the basic structural element of biological membranes. They separate the various cell compartments found in eukaryotic cells and form an outer barrier (cell membrane or plasma membrane) of eukaryotic and prokaryotic cells separating the cytoplasm from the extra-cellular space. The composition of phospholipid bilayers varies with the cell type and function of the membrane. It commonly contains, for example, charged lipids, neutral or zwitterionic lipids, glycolipids, cholesterol, and sphingomyelin. The hydrocarbon core of the lipid bilayer forms a passive barrier for ions, sugars, and other metabolites. The lipid components of the membrane provide a matrix for incorporation of membrane proteins that are involved in cell processes such as transport of ions and molecules across the membrane, cell signaling, and ligand recognition (receptors). Biological phospholipid bilayers are actively kept in a fluid state [Sin72], allowing lipids and membrane proteins to diffuse in the lipid bilayer and to form functional domains for cell processes.