Lamellar phase in the context of "Nuclear magnetic resonance"

In cell biology, a vesicle is an organelle within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form naturally during the processes of secretion (exocytosis), uptake (endocytosis), and the transport of materials within the plasma membrane. Alternatively, they may be prepared artificially, in which case they are called liposomes (not to be confused with lysosomes). If there is only one phospholipid bilayer, the vesicles are called unilamellar liposomes; otherwise they are called multilamellar liposomes. The membrane enclosing the vesicle is also a lamellar phase, similar to that of the plasma membrane, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle.

Vesicles perform a variety of functions. Because it is separated from the cytosol, the inside of the vesicle can be made to be different from the cytosolic environment. For this reason, vesicles are a basic tool used by the cell for organizing cellular substances. Vesicles are involved in metabolism, transport, buoyancy control, and temporary storage of food and enzymes. They can also act as chemical reaction chambers.

Annular lipids (also called shell lipids or boundary lipids) are a set of lipids or lipidic molecules which preferentially bind or stick to the surface of membrane proteins in biological cells. They constitute a layer, or an annulus/ shell, of lipids which are partially immobilized due to the existence of lipid-protein interactions. Polar headgroups of these lipids bind to the hydrophilic part of the membrane protein(s) at the inner and outer surfaces of lipid bilayer membrane. The hydrophobic surface of the membrane proteins is bound to the apposed lipid fatty acid chains of the membrane bilayer. For integral membrane proteins spanning the thickness of the membrane bilayer, these annular/shell lipids may act like a lubricating layer on the proteins' surfaces, thereby facilitating almost free rotation and lateral diffusion of membrane proteins within the 2-dimensional expanse of the biological membrane(s). Outside the layer of shell/annular lipids, lipids are not tied down to protein molecules. However, they may be slightly restricted in their segmental motion freedom due to mild peer pressure of protein molecules, if present in high concentration, which arises from extended influence of protein-lipid interaction. Membrane areas away from protein molecules contain lamellar phase bulk lipids, which are largely free from any restraining effects due to protein-lipid interactions. Thermal denaturation of membrane proteins may destroy the secondary and tertiary structure of membrane proteins, exposing newer surfaces to membrane lipids and therefore increasing the number of lipids molecules in the annulus/shell layer. This phenomenon can be studied by the spin label electron paramagnetic resonance technique. The protein-lipid binding are dependent on OmpF pH levels and their structural features and location of the membranes. When said lipids bind to OmpF it is sensitive to changes that may occur in the electrospray polarity.

In biophysics and colloidal chemistry, polymorphism is the ability of lipids to aggregate in a variety of ways, giving rise to structures of different shapes, known as "phases". This can be in the form of spheres of lipid molecules (micelles), pairs of layers that face one another (lamellar phase, observed in biological systems as a lipid bilayer), a tubular arrangement (hexagonal), or various cubic phases (Fd3m, Im3m, Ia3m, Pn3m, and Pm3m being those discovered so far). More complicated aggregations have also been observed, such as rhombohedral, tetragonal and orthorhombic phases.

It forms an important part of current academic research in the fields of membrane biophysics (polymorphism), biochemistry (biological impact) and organic chemistry (synthesis).