This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine.The three main structures phospholipids form in solution; the liposome (a closed bilayer), the micelle and the bilayer.
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many viruses are made of a lipid bilayer, as are the nuclear membrane surrounding the cell nucleus, and membranes of the membrane-bound organelles in the cell. The lipid bilayer is the barrier that keeps ions, proteins and other molecules where they are needed and prevents them from diffusing into areas where they should not be. Lipid bilayers are ideally suited to this role, even though they are only a few nanometers in width,[1] because they are impermeable to most water-soluble (hydrophilic) molecules. Bilayers are particularly impermeable to ions, which allows cells to regulate salt concentrations and pH by transporting ions across their membranes using proteins called ion pumps.
Biological bilayers are usually composed of amphiphilic phospholipids that have a hydrophilic phosphate head and a hydrophobic tail consisting of two fatty acid chains. Phospholipids with certain head groups can alter the surface chemistry of a bilayer and can, for example, serve as signals as well as "anchors" for other molecules in the membranes of cells.[2] Just like the heads, the tails of lipids can also affect membrane properties, for instance by determining the phase of the bilayer. The bilayer can adopt a solid gel phase state at lower temperatures but undergo phase transition to a fluid state at higher temperatures, and the chemical properties of the lipids' tails influence at which temperature this happens. The packing of lipids within the bilayer also affects its mechanical properties, including its resistance to stretching and bending. Many of these properties have been studied with the use of artificial "model" bilayers produced in a lab. Vesicles made by model bilayers have also been used clinically to deliver drugs.
The structure of biological membranes typically includes several types of molecules in addition to the phospholipids comprising the bilayer. A particularly important example in animal cells is cholesterol, which helps strengthen the bilayer and decrease its permeability. Cholesterol also helps regulate the activity of certain integral membrane proteins. Integral membrane proteins function when incorporated into a lipid bilayer, and they are held tightly to the lipid bilayer with the help of an annular lipid shell. Because bilayers define the boundaries of the cell and its compartments, these membrane proteins are involved in many intra- and inter-cellular signaling processes. Certain kinds of membrane proteins are involved in the process of fusing two bilayers together. This fusion allows the joining of two distinct structures as in the acrosome reaction during fertilization of an egg by a sperm, or the entry of a virus into a cell. Because lipid bilayers are fragile and invisible in a traditional microscope, they are a challenge to study. Experiments on bilayers often require advanced techniques like electron microscopy and atomic force microscopy.
^Andersen, Olaf S.; Koeppe, II, Roger E. (June 2007). "Bilayer Thickness and Membrane Protein Function: An Energetic Perspective". Annual Review of Biophysics and Biomolecular Structure. 36 (1): 107–130. doi:10.1146/annurev.biophys.36.040306.132643. PMID 17263662. S2CID 6521535.
^Divecha, Nullin; Irvine, Robin F (27 January 1995). "Phospholipid signaling". Cell. 80 (2): 269–278. doi:10.1016/0092-8674(95)90409-3. PMID 7834746. S2CID 14120598.
The lipidbilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a...
A model lipidbilayer is any bilayer assembled in vitro, as opposed to the bilayer of natural cell membranes or covering various sub-cellular structures...
functional cell membranes. According to this biological model, there is a lipidbilayer (two molecules thick layer consisting primarily of amphipathic phospholipids)...
Lipidbilayer characterization is the use of various optical, chemical and physical probing methods to study the properties of lipidbilayers. Many of...
One property of a lipidbilayer is the relative mobility (fluidity) of the individual lipid molecules and how this mobility changes with temperature....
space). The cell membrane consists of a lipidbilayer, made up of two layers of phospholipids with cholesterols (a lipid component) interspersed between them...
membrane biology, fusion is the process by which two initially distinct lipidbilayers merge their hydrophobic cores, resulting in one interconnected structure...
biological membrane is a form of lamellar phase lipid bilayer. The formation of lipidbilayers is an energetically preferred process when the glycerophospholipids...
Membrane lipids are a group of compounds (structurally similar to fats and oils) which form the lipidbilayer of the cell membrane. The three major classes...
integral membrane proteins, or penetrate the peripheral regions of the lipidbilayer. The regulatory protein subunits of many ion channels and transmembrane...
a small artificial vesicle, spherical in shape, having at least one lipidbilayer. Due to their hydrophobicity and/or hydrophilicity, biocompatibility...
types of lipids involved in lipid metabolism include: Membrane lipids: Phospholipids: Phospholipids are a major component of the lipidbilayer of the cell...
membrane fluidity environment of the lipidbilayer with the presence of an annular lipid shell, consisting of lipid molecules bound tightly to the surface...
that this barrier membrane consisted of two molecular layers of lipids—a lipidbilayer. New tools over the next few decades confirmed this theory, but...
Lipidbilayer mechanics is the study of the physical material properties of lipidbilayers, classifying bilayer behavior with stress and strain rather...
packed than the surrounding bilayer, but float freely within the membrane bilayer. Although more common in the cell membrane, lipid rafts have also been reported...
membrane comprises a typical lipidbilayer, similar to what can be found in virtually all human cells. Simply put, this lipidbilayer is composed of cholesterol...
electronic properties as bilayer systems and are an active area of current research. In biology, a common example is the lipidbilayer, which describes the...
a membrane is a phospholipid bilayer that forms in a water-based environment due to the hydrophilic nature of the lipid head and the hydrophobic nature...
anaesthetic effect is exerted through some perturbation of the lipidbilayer. Several types of bilayer perturbations were proposed to cause anaesthetic effect...
lipid cored Liposome, lipidbilayer shell, an earlier form with some limitations Lipoplex, a complex of plasmid or linear DNA and lipids Targeted drug delivery...
extrude their contents, which are predominantly lipids. The lipids ultimately form the lamellar lipidbilayer that surrounds corneocytes and also contributes...
They can form lipidbilayers because of their amphiphilic characteristic. In eukaryotes, cell membranes also contain another class of lipid, sterol, interspersed...
fluidity refers to the viscosity of the lipidbilayer of a cell membrane or a synthetic lipid membrane. Lipid packing can influence the fluidity of the...
–40 mV. All animal cells are surrounded by a membrane composed of a lipidbilayer with proteins embedded in it. The membrane serves as both an insulator...
but sensitive to local stress, most likely tension in the surrounding lipidbilayer. Mechanosensitive channels were discovered in 1983 in the skeletal muscle...
bilayers separated by bulk liquid. In biophysics, polar lipids (mostly, phospholipids, and rarely, glycolipids) pack as a liquid crystalline bilayer,...
associate with integral membrane proteins, or independently insert in the lipidbilayer in several ways. Three-dimensional structures of ~160 different integral...
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