Lipid bilayer

phospholipid bilayerlipid membranelipid bilayersbilayerlipid membranesmembranephospholipid membranephospholipid bilayersmembranesbilayers
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules.wikipedia
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Nuclear envelope

nuclear membraneinner membraneperinuclear space
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 other membranes surrounding sub-cellular structures.
The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes which in eukaryotic cells surrounds the nucleus, which encases the genetic material.

Polar membrane

membrane
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules.
A polar membrane is a lipid membrane that expresses polarity.

Phospholipid

phospholipidsDOPEinterface region
Biological bilayers are usually composed of amphiphilic phospholipids that have a hydrophilic phosphate head and a hydrophobic tail consisting of two fatty acid chains. It has even been proposed that the very first form of life may have been a simple lipid vesicle with virtually its sole biosynthetic capability being the production of more phospholipids.
They can form lipid bilayers because of their amphiphilic characteristic.

Biological membrane

membranemembranesbiological membranes
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 other membranes surrounding sub-cellular structures.
Biological membranes, in the form of eukaryotic cell membranes, consist of a phospholipid bilayer with embedded, integral and peripheral proteins used in communication and transportation of chemicals and ions.

Cell membrane

plasma membranemembranecell membranes
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 other membranes surrounding sub-cellular structures.
Cell membrane consists of a lipid bilayer, including cholesterols (a lipid component) that sit between phospholipids to maintain their fluidity under various temperature, in combination with membrane proteins such as integral proteins, and peripheral proteins that go across inside and outside of the membrane serving as membrane transporter, and loosely attached to the outer (peripheral) side of the cell membrane acting as several kinds of enzymes shaping the cell, respectively.

Lipid

lipidsglycerolipidfat
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules.
Glycerophospholipids, usually referred to as phospholipids (though sphingomyelins are also classified as phospholipids), are ubiquitous in nature and are key components of the lipid bilayer of cells, as well as being involved in metabolism and cell signaling.

Cholesterol

total cholesteroldietary cholesterolserum cholesterol
A particularly important example in animal cells is cholesterol, which helps strengthen the bilayer and decrease its permeability.
The hydroxyl group of each cholesterol molecule interacts with water molecules surrounding the membrane, as do the polar heads of the membrane phospholipids and sphingolipids, while the bulky steroid and the hydrocarbon chain are embedded in the membrane, alongside the nonpolar fatty-acid chain of the other lipids.

Cell (biology)

cellcellscellular
These membranes are flat sheets that form a continuous barrier around all cells.
This membrane serves to separate and protect a cell from its surrounding environment and is made mostly from a double layer of phospholipids, which are amphiphilic (partly hydrophobic and partly hydrophilic).

Organism

organismsflora and faunaliving organisms
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 other membranes surrounding sub-cellular structures.
A bilayer of phospholipids makes up the membrane of cells that constitutes a barrier, containing everything within the cell and preventing compounds from freely passing into, and out of, the cell.

Phosphatidylethanolamine

cephalinphosphatidyl ethanolaminePE
In human red blood cells, the inner (cytoplasmic) leaflet is composed mostly of phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol and its phosphorylated derivatives.
It can mainly be found in the inner (cytoplasmic) leaflet of the lipid bilayer.

Annular lipid shell

annular lipids
Integral membrane proteins function when incorporated into a lipid bilayer, and they are held tightly to lipid bilayer with the help of an annular lipid shell.
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.

Biosynthesis

productionsynthesisbiosynthetic
It has even been proposed that the very first form of life may have been a simple lipid vesicle with virtually its sole biosynthetic capability being the production of more phospholipids.
Examples of these biosynthetic pathways include the production of lipid membrane components and nucleotides.

Organelle

organellescell organellescell organelle
See Organelle. In contrast, eukaryotes have a range of organelles including the nucleus, mitochondria, lysosomes and endoplasmic reticulum.
Organelles are either separately enclosed within their own lipid bilayers (also called membrane-bound organelles) or are spatially distinct functional units without a surrounding lipid bilayer (non-membrane bound organelles).

Vesicle (biology and chemistry)

vesiclesvesiclemembrane trafficking
It has even been proposed that the very first form of life may have been a simple lipid vesicle with virtually its sole biosynthetic capability being the production of more phospholipids. Vesicles made by model bilayers have also been used clinically to deliver drugs.
In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer.

Amphiphile

amphipathicamphiphilicamphiphiles
Biological bilayers are usually composed of amphiphilic phospholipids that have a hydrophilic phosphate head and a hydrophobic tail consisting of two fatty acid chains.
They arrange themselves into bilayers, by positioning their polar groups towards the surrounding aqueous medium, and their lipophilic chains towards the inside of the bilayer, defining a non-polar region between two polar ones.

Bacteria

bacteriumbacterialEubacteria
One common example of such a modification in nature is the lipopolysaccharide coat on a bacterial outer membrane, which helps retain a water layer around the bacterium to prevent dehydration.
In contrast, gram-negative bacteria have a relatively thin cell wall consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins.

Flippase

floppaseflip-flopflippases
Lipid asymmetry arises, at least in part, from the fact that most phospholipids are synthesised and initially inserted into the inner monolayer: those that constitute the outer monolayer are then transported from the inner monolayer by a class of enzymes called flippases.
The possibility of active maintenance of an asymmetric distribution of molecules in the phospholipid bilayer was predicted in the early 1970s by Mark Bretscher.

Atomic force microscopy

atomic force microscopeAFMatomic-force microscopy
Experiments on bilayers often require advanced techniques like electron microscopy and atomic force microscopy.
Tapping mode imaging is gentle enough even for the visualization of supported lipid bilayers or adsorbed single polymer molecules (for instance, 0.4 nm thick chains of synthetic polyelectrolytes) under liquid medium.

Lipid bilayer fusion

membrane fusionfusionfuse
These vesicles fuse with the cell membrane at the pre-synaptic terminal and release its contents to the exterior of the cell.
In membrane biology, fusion is the process by which two initially distinct lipid bilayers merge their hydrophobic cores, resulting in one interconnected structure.

Phospholipid scramblase

scramblasescramblaseslipid flip-flop
During programmed cell death a protein called a scramblase equilibrates this distribution, displaying phosphatidylserine on the extracellular bilayer face.
Scramblase is a protein responsible for the translocation of phospholipids between the two monolayers of a lipid bilayer of a cell membrane.

Mitochondrion

mitochondriamitochondrialmitochondrial membrane
In contrast, eukaryotes have a range of organelles including the nucleus, mitochondria, lysosomes and endoplasmic reticulum.

Endoplasmic reticulum

rough endoplasmic reticulumERsmooth endoplasmic reticulum
In contrast, eukaryotes have a range of organelles including the nucleus, mitochondria, lysosomes and endoplasmic reticulum.
The phospholipid membrane encloses the cisternal space (or lumen), which is continuous with the perinuclear space but separate from the cytosol.

Phase transition

phase transitionsorder parameterphase change
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.
Examples include the lipid bilayer formation, the coil-globule transition in the process of protein folding and DNA melting, liquid crystal-like transitions in the process of DNA condensation, and cooperative ligand binding to DNA and proteins with the character of phase transition.

HIV

human immunodeficiency virusHIV-positiveHIV positive
The HIV virus evades the immune system in part by grafting these proteins from the host membrane onto its own surface.
This is, in turn, surrounded by the viral envelope, that is composed of the lipid bilayer taken from the membrane of a human host cell when the newly formed virus particle buds from the cell.

Ion channel

ion channelschannelchannels
The sensitivity of this system is such that even the activity of single ion channels can be resolved.
Such "multi-subunit" assemblies usually involve a circular arrangement of identical or homologous proteins closely packed around a water-filled pore through the plane of the membrane or lipid bilayer.