Phospholipid

Phospholipid arrangement in cell membranes.
Phosphatidylcholine is the major component of lecithin. It is also a source for choline in the synthesis of acetylcholine in cholinergic neurons.
Phospholipid bilayers are the main structural component of the cell membranes.

Alcohol residue .

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Amphiphile

Chemical compound possessing both hydrophilic (water-loving, polar) and lipophilic (fat-loving) properties.

Phospholipids, such as this glycerophospholipid, have amphipathic character.
Cross-section view of the structures that can be formed by biological amphiphiles in aqueous solutions. Unlike this illustration, micelles are usually formed by non-biological, single-chain, amphiphiles, soaps or detergents, since it is difficult to fit two chains into this shape.
The lipid bilayer, the material that makes up cell membranes.

The phospholipid amphiphiles are the major structural component of cell membranes.

Phosphatidylcholine

1-Oleoyl-2-palmitoyl-phosphatidylcholine
Palmitoyl-oleyl-sn-phosphatidylcholine, a phosphatidylcholine.
General structural formula of phosphatidylcholines
Membrane lipids
Choline metabolism
Phosphatidate
Choline

Phosphatidylcholines (PC) are a class of phospholipids that incorporate choline as a headgroup.

Lipid bilayer

Thin polar membrane made of two layers of lipid molecules.

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.
Schematic cross sectional profile of a typical lipid bilayer. There are three distinct regions: the fully hydrated headgroups, the fully dehydrated alkane core and a short intermediate region with partial hydration. Although the head groups are neutral, they have significant dipole moments that influence the molecular arrangement.
TEM image of a bacterium. The furry appearance on the outside is due to a coat of long-chain sugars attached to the cell membrane. This coating helps trap water to prevent the bacterium from becoming dehydrated.
Diagram showing the effect of unsaturated lipids on a bilayer. The lipids with an unsaturated tail (blue) disrupt the packing of those with only saturated tails (black). The resulting bilayer has more free space and is, as a consequence, more permeable to water and other small molecules.
Illustration of a GPCR signaling protein. In response to a molecule such as a hormone binding to the exterior domain (blue) the GPCR changes shape and catalyzes a chemical reaction on the interior domain (red). The gray feature is the surrounding bilayer.
Transmission Electron Microscope (TEM) image of a lipid vesicle. The two dark bands around the edge are the two leaflets of the bilayer. Historically, similar images confirmed that the cell membrane is a bilayer
Human red blood cells viewed through a fluorescence microscope. The cell membrane has been stained with a fluorescent dye. Scale bar is 20μm.
3d-Adapted AFM images showing formation of transmembrane pores (holes) in supported lipid bilayer
Illustration of a typical AFM scan of a supported lipid bilayer. The pits are defects in the bilayer, exposing the smooth surface of the substrate underneath.
Structure of a potassium ion channel. The alpha helices penetrate the bilayer (boundaries indicated by red and blue lines), opening a hole through which potassium ions can flow
Schematic illustration of pinocytosis, a type of endocytosis
Exocytosis of outer membrane vesicles (MV) liberated from inflated periplasmic pockets (p) on surface of human Salmonella 3,10:r:- pathogens docking on plasma membrane of macrophage cells (M) in chicken ileum, for host-pathogen signaling in vivo.
Schematic showing two possible conformations of the lipids at the edge of a pore. In the top image the lipids have not rearranged, so the pore wall is hydrophobic. In the bottom image some of the lipid heads have bent over, so the pore wall is hydrophilic.
Illustration of lipid vesicles fusing showing two possible outcomes: hemifusion and full fusion. In hemifusion, only the outer bilayer leaflets mix. In full fusion both leaflets as well as the internal contents mix.
Schematic illustration of the process of fusion through stalk formation.
Diagram of the action of SNARE proteins docking a vesicle for exocytosis. Complementary versions of the protein on the vesicle and the target membrane bind and wrap around each other, drawing the two bilayers close together in the process.

Biological bilayers are usually composed of amphiphilic phospholipids that have a hydrophilic phosphate head and a hydrophobic tail consisting of two fatty acid chains.

Docosahexaenoic acid

Omega-3 fatty acid that is a primary structural component of the human brain, cerebral cortex, skin, and retina.

Algae-based DHA supplements

DHA is a major fatty acid in brain phospholipids and the retina.

Hydrophobic effect

Observed tendency of nonpolar substances to aggregate in an aqueous solution and exclude water molecules.

A droplet of water forms a spherical shape, minimizing contact with the hydrophobic leaf.
Dynamic hydrogen bonds between molecules of liquid water

They are also important to cell membranes composed of amphiphilic phospholipids that prevent the internal aqueous environment of a cell from mixing with external water.

Lecithin

Generic term to designate any group of yellow-brownish fatty substances occurring in animal and plant tissues which are amphiphilic – they attract both water and fatty substances (and so are both hydrophilic and lipophilic), and are used for smoothing food textures, emulsifying, homogenizing liquid mixtures, and repelling sticking materials.

An example of a phosphatidylcholine, a type of phospholipid in lecithin. Shown in – choline residue and phosphate group; – glycerol residue;  – monounsaturated fatty acid residue;  – saturated fatty acid residue.
Soy lecithin for sale at a grocery store in Uruguay

In aqueous solution, its phospholipids can form either liposomes, bilayer sheets, micelles, or lamellar structures, depending on hydration and temperature.

Phosphatidylinositol 4,5-bisphosphate

Phospholipid arrangement in cell membranes.

Phosphatidylinositol 4,5-bisphosphate or PtdIns(4,5)P2, also known simply as PIP2 or PI(4,5)P2, is a minor phospholipid component of cell membranes.

Phospholipase C

Cleavage sites of phospholipases. Phospholipase C enzymes cut just before the phosphate attached to the R3 moiety.
Comparison of C2 domain of mammalian PI-PLC in red and C2-like domain of Bacillus cereus in cyan.
General reaction catalyzed by phospholipase C
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Phospholipase C (PLC) is a class of membrane-associated enzymes that cleave phospholipids just before the phosphate group (see figure).

Phosphatidylserine

Biosynthesis of phosphatidylserine

Phosphatidylserine (abbreviated Ptd-L-Ser or PS) is a phospholipid and is a component of the cell membrane.

Phosphatidylethanolamine

Biosynthesis of various phospholipids (including phosphatidylethanolamine) in bacteria
Ethanolamine

Phosphatidylethanolamine (PE) is a class of phospholipids found in biological membranes.