
Phospholipids are a class of
lipid
Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing ...
s whose molecule has a
hydrophilic "head" containing a
phosphate
Phosphates are the naturally occurring form of the element phosphorus.
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthop ...
group and two
hydrophobic
In chemistry, hydrophobicity is the chemical property of a molecule (called a hydrophobe) that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water.
Hydrophobic molecules tend to be nonpolar and, thu ...
"tails" derived from
fatty acid
In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...
s, joined by an
alcohol
Alcohol may refer to:
Common uses
* Alcohol (chemistry), a class of compounds
* Ethanol, one of several alcohols, commonly known as alcohol in everyday life
** Alcohol (drug), intoxicant found in alcoholic beverages
** Alcoholic beverage, an alco ...
residue (usually a
glycerol
Glycerol () is a simple triol compound. It is a colorless, odorless, sweet-tasting, viscous liquid. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pha ...
molecule). Marine phospholipids typically have
omega-3 fatty acids
EPA and
DHA integrated as part of the phospholipid molecule. The phosphate group can be modified with simple organic molecules such as
choline,
ethanolamine or
serine.
Phospholipids are a key component of all
cell membrane
The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
s. They can form
lipid bilayer
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes form a continuous barrier around all cell (biology), cells. The cell membranes of almost all organisms and many viruses a ...
s because of their
amphiphilic characteristic. In
eukaryote
The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
s, cell membranes also contain another class of lipid,
sterol
A sterol is any organic compound with a Skeletal formula, skeleton closely related to Cholestanol, cholestan-3-ol. The simplest sterol is gonan-3-ol, which has a formula of , and is derived from that of gonane by replacement of a hydrogen atom on ...
, interspersed among the phospholipids. The combination provides fluidity in two dimensions combined with mechanical strength against rupture. Purified phospholipids are produced commercially and have found applications in
nanotechnology
Nanotechnology is the manipulation of matter with at least one dimension sized from 1 to 100 nanometers (nm). At this scale, commonly known as the nanoscale, surface area and quantum mechanical effects become important in describing propertie ...
and
materials science
Materials science is an interdisciplinary field of researching and discovering materials. Materials engineering is an engineering field of finding uses for materials in other fields and industries.
The intellectual origins of materials sci ...
.
The first phospholipid identified in 1847 as such in biological tissues was
lecithin, or
phosphatidylcholine, in the egg yolk of chickens by the French chemist and pharmacist
Theodore Nicolas Gobley.
Phospholipids in biological membranes
Arrangement
The phospholipids are
amphiphilic. The hydrophilic end usually contains a negatively charged phosphate group, and the hydrophobic end usually consists of two "tails" that are long
fatty acid
In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...
residues.
In aqueous solutions, phospholipids are driven by
hydrophobic interactions, which result in the fatty acid tails aggregating to minimize interactions with the water molecules. The result is often a
phospholipid bilayer: a membrane that consists of two layers of oppositely oriented phospholipid molecules, with their heads exposed to the liquid on both sides, and with the tails directed into the membrane. That is the dominant structural motif of the membranes of all
cells and of some other biological structures, such as
vesicles or
virus
A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...
coatings.

In biological membranes, the phospholipids often occur with other molecules (e.g.,
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
s,
glycolipid
Glycolipids () are lipids with a carbohydrate attached by a glycosidic (covalent) bond. Their role is to maintain the stability of the cell membrane and to facilitate cellular recognition, which is crucial to the immune response and in the c ...
s,
sterol
A sterol is any organic compound with a Skeletal formula, skeleton closely related to Cholestanol, cholestan-3-ol. The simplest sterol is gonan-3-ol, which has a formula of , and is derived from that of gonane by replacement of a hydrogen atom on ...
s) in a
bilayer such as a
cell membrane
The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
. Lipid bilayers occur when hydrophobic tails line up against one another, forming a membrane of hydrophilic heads on both sides facing the water.
Dynamics
These specific properties allow phospholipids to play an important role in the cell membrane. Their movement can be described by the
fluid mosaic model
The fluid mosaic model explains various characteristics regarding the structure of functional cell membranes. According to this Scientific model, biological model, there is a lipid bilayer (two molecules thick layer consisting primarily of Amphip ...
, which describes the membrane as a mosaic of lipid molecules that act as a solvent for all the substances and proteins within it, so proteins and lipid molecules are then free to diffuse laterally through the lipid matrix and migrate over the membrane.
Sterol
A sterol is any organic compound with a Skeletal formula, skeleton closely related to Cholestanol, cholestan-3-ol. The simplest sterol is gonan-3-ol, which has a formula of , and is derived from that of gonane by replacement of a hydrogen atom on ...
s contribute to membrane fluidity by hindering the packing together of phospholipids. However, this model has now been superseded, as through the study of
lipid polymorphism it is now known that the behaviour of lipids under physiological (and other) conditions is not simple.
Main phospholipids
Diacylglyceride structures
: ''See:
Glycerophospholipid
Glycerophospholipids or phosphoglycerides are glycerol-based phospholipids. They are the main component of biological membranes in eukaryotic cells. They are a type of lipid, of which its composition affects membrane structure and properties. T ...
''
*
Phosphatidic acid (phosphatidate) (PA)
*
Phosphatidylethanolamine (cephalin) (PE)
*
Phosphatidylcholine (lecithin) (PC)
*
Phosphatidylserine (PS)
* Phosphoinositides:
**
Phosphatidylinositol (PI)
**
Phosphatidylinositol 3-phosphate (PI3P)
**
Phosphatidylinositol 4-phosphate (PI4P)
**
Phosphatidylinositol 5-phosphate
Phosphatidylinositol 5-phosphate (PtdIns5P) is a phosphoinositide, one of the phosphorylated derivatives of phosphatidylinositol (PtdIns), that are well-established membrane-anchored regulatory molecules. Phosphoinositides participate in signaling ...
(PI5P)
**
Phosphatidylinositol 4,5-bisphosphate (PIP2)
**
Phosphatidylinositol (3,4,5)-trisphosphate (PIP3)
Phosphosphingolipids
: ''See
Sphingolipid
Sphingolipids are a class of lipids containing a backbone of sphingoid bases, which are a set of aliphatic amino alcohols that includes sphingosine. They were discovered in brain extracts in the 1870s and were named after the mythological sp ...
''
* Ceramide phosphorylcholine (
Sphingomyelin) (SPH)
* Ceramide phosphorylethanolamine (
Sphingomyelin) (Cer-PE)
* Ceramide phosphoryllipid
Applications
Phospholipids have been widely used to prepare liposomal, ethosomal and other nanoformulations of topical, oral and
parenteral drugs for differing reasons like improved bio-availability, reduced toxicity and increased permeability across membranes. Liposomes are often composed of
phosphatidylcholine-enriched phospholipids and may also contain mixed phospholipid chains with
surfactant
Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a Blend word, blend of "surface-active agent",
coined in ...
properties. The ethosomal formulation of
ketoconazole
Ketoconazole, sold under the brand name Nizoral, among others, is an antiandrogen, antifungal drug, antifungal, and antiglucocorticoid medication used to treat a number of fungal infections. Applied to the skin it is used for fungal skin inf ...
using phospholipids is a promising option for transdermal delivery in fungal infections. Advances in phospholipid research lead to exploring these biomolecules and their conformations using lipidomics.
Simulations
Computational simulations of phospholipids are often performed using
molecular dynamics
Molecular dynamics (MD) is a computer simulation method for analyzing the Motion (physics), physical movements of atoms and molecules. The atoms and molecules are allowed to interact for a fixed period of time, giving a view of the dynamics ( ...
with
force fields such as
GROMOS,
CHARMM
Chemistry at Harvard Macromolecular Mechanics (CHARMM) is the name of a widely used set of force fields for molecular dynamics, and the name for the molecular dynamics simulation and analysis computer software package associated with them. The CH ...
, or
AMBER
Amber is fossilized tree resin. Examples of it have been appreciated for its color and natural beauty since the Neolithic times, and worked as a gemstone since antiquity."Amber" (2004). In Maxine N. Lurie and Marc Mappen (eds.) ''Encyclopedia ...
.
Characterization
Phospholipids are optically highly
birefringent, i.e. their refractive index is different along their axis as opposed to perpendicular to it. Measurement of
birefringence
Birefringence, also called double refraction, is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are described as birefrin ...
can be achieved using cross polarisers in a microscope to obtain an image of e.g.
vesicle walls or using techniques such as
dual polarisation interferometry to quantify lipid order or disruption in supported bilayers.
Analysis
There are no simple methods available for analysis of phospholipids, since the close range of polarity between different phospholipid species makes detection difficult. Oil chemists often use spectroscopy to determine total phosphorus abundance and then calculate approximate mass of phospholipids based on molecular weight of expected fatty acid species. Modern lipid profiling employs more absolute methods of analysis, with
NMR spectroscopy, particularly
31P-NMR, while
HPLC-
ELSD provides relative values.
Phospholipid synthesis
Phospholipid synthesis occurs in the cytosolic side of
ER membrane that is studded with proteins that act in synthesis (
GPAT and LPAAT acyl transferases, phosphatase and choline phosphotransferase) and allocation (
flippase and floppase). Eventually a vesicle will bud off from the ER containing phospholipids destined for the cytoplasmic cellular membrane on its exterior leaflet and phospholipids destined for the exoplasmic cellular membrane on its inner leaflet.
Sources
Common sources of industrially produced phospholipids are soya, rapeseed, sunflower, chicken eggs, bovine milk, fish eggs etc. Phospholipids for gene delivery, such as
distearoylphosphatidylcholine and
dioleoyl-3-trimethylammonium propane, are produced synthetically. Each source has a unique profile of individual phospholipid species, as well as fatty acids, and consequently differing applications in food, nutrition, pharmaceuticals, cosmetics, and drug delivery.
In signal transduction
Some types of phospholipid can be split to produce products that function as
second messengers in
signal transduction
Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a biochemical cascade, series of molecular events. Proteins responsible for detecting stimuli are generally termed receptor (biology), rece ...
. Examples include
phosphatidylinositol (4,5)-bisphosphate (PIP
2), that can be split by the enzyme
phospholipase C into
inositol triphosphate (IP
3) and
diacylglycerol (DAG), which both carry out the
functions of the Gq type of G protein in response to various stimuli and intervene in various processes from
long term depression in neurons to
leukocyte signal pathways started by
chemokine receptors.
Phospholipids also intervene in
prostaglandin signal pathways as the raw material used by
lipase enzymes to produce the prostaglandin precursors. In plants they serve as the raw material to produce
jasmonic acid, a
plant hormone
Plant hormones (or phytohormones) are signal molecules, produced within plants, that occur in extremely low concentrations. Plant hormones control all aspects of plant growth and development, including embryogenesis, the regulation of Organ (anat ...
similar in structure to prostaglandins that mediates defensive responses against pathogens.
Food technology
Phospholipids can act as
emulsifiers, enabling oils to form a
colloid
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others exte ...
with water. Phospholipids are one of the components of
lecithin, which is found in egg yolks, as well as being extracted from
soybean
The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean. Soy is a staple crop, the world's most grown legume, and an important animal feed.
Soy is a key source o ...
s, and is used as a
food additive
Food additives are substances added to food to preserve flavor or enhance taste, appearance, or other sensory qualities. Some additives, such as vinegar ( pickling), salt ( salting), smoke ( smoking) and sugar ( crystallization), have been used f ...
in many products and can be purchased as a
dietary supplement
A dietary supplement is a manufactured product intended to supplement a person's diet by taking a pill (pharmacy), pill, capsule (pharmacy), capsule, tablet (pharmacy), tablet, powder, or liquid. A supplement can provide nutrients eithe ...
. Lysolecithins are typically used for water–oil emulsions like
margarine, due to their higher
HLB ratio.
Phospholipid derivatives
: ''See table below for an extensive list.''
* Natural phospholipid derivates:
*: egg PC (
Egg lecithin), egg PG, soy PC, hydrogenated soy PC,
sphingomyelin as natural phospholipids.
* Synthetic phospholipid derivates:
**
Phosphatidic acid (DMPA, DPPA, DSPA)
**
Phosphatidylcholine (DDPC, DLPC, DMPC,
DPPC, DSPC, DOPC,
POPC, DEPC)
**
Phosphatidylglycerol (DMPG, DPPG, DSPG, POPG)
**
Phosphatidylethanolamine (DMPE, DPPE, DSPE DOPE)
**
Phosphatidylserine (DOPS)
** PEG phospholipid (mPEG-phospholipid, polyglycerin-phospholipid, functionalized-phospholipid, terminal activated-phospholipid)
Abbreviations used and chemical information of glycerophospholipids
See also
*
Cable theory
*
Galactolipid
*
Sulfolipid
References
{{Authority control
Anionic surfactants