phospholipid

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A lipid that contains one or more phosphate groups. Phospholipids are amphipathic in nature; that is, each molecule consists of a hydrophilic (water-loving) portion and a hydrophobic (water-hating) portion. Due to the amphipathic nature and insolubility in water, phospholipids are ideal compounds for forming the biological membrane. See also Lipid.

There are two classes of phospholipids: those that have a glycerol backbone and those that contain sphingosine. Both classes are present in the biological membrane. Phospholipids that contain a glycerol backbone are called phosphoglycerides (or glycerophospholipids), which are the most abundant class of phospholipid found in nature. The most abundant types of naturally occurring phosphoglyceride are phosphatidylcholine (lecithin), phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, phosphatidylglycerol, and cardiolipin. The structural diversity within each type of phosphoglyceride is due to the variability of the chain length and degree of saturation of the fatty acid ester groups.

Sphingomyelin is the major sphingosine-containing phospholipid. Its general structure consists of a fatty acid attached to sphingosine by an amide linkage.

A bilayer membrane is formed spontaneously when phospholipids are dispersed in an aqueous solution. In this bilayer structure, phospholipids are arranged in two leaflets with the hydrophobic tails facing each other, and the hydrophilic ends exposed to the aqueous medium. Differences in the head group, the chain length, and the degree of saturation of fatty acids in the hydrophobic end are important factors in determining the shape of the bilayer. Individual phospholipid molecules are able to move freely in the lateral plane of the bilayer but not in the transverse plane (flip-flop). Small uncharged molecules are able to diffuse through the bilayer structure, but the permeability of larger or charged molecules is restricted. The arrangement of phospholipid molecules into a bilayer in an aqueous medium follows the laws of thermodynamics and represents the structural basis for the formation of all biological membranes.

For a long time, phospholipids were regarded as merely building blocks for the biological membrane. It was discovered in the mid-1970s, however, that phospholipids participate in the transduction of biological signals across the membrane. For example, when the hormone vasopressin is bound to its receptor on the plasma membrane of a liver cell, the binding sets off a cascade of reactions which result in enhanced breakdown of glycogen in the liver cell, thus producing more glucose. See also Second messengers.

A special form of phosphoglyceride, 1-alkyl-2-acetyl-glycero-3-phosphocholine, acts as a very powerful biological mediator. It causes the aggregation and degranulation of blood platelets, and is known as platelet-activating factor (PAF).

Phospholipases are responsible for the degradation of phosphoglycerides. These enzymes are found in all tissues and in the pancreatic juice. A number of toxins and venoms have very high phospholipase activity, and several pathogenic bacteria produce phospholipases that dissolve cell membrane and allow the spread of infection. There are very few inherited diseases associated with the metabolism of phosphoglycerides; presumably, such genetic defects would be lethal during the early stage of cellular development.

Sphingomyelinase, a lysosomal enzyme, hydrolytically degrades sphingomyelin. A genetic disorder caused by a defect in the production of sphingomyelinase, called Niemann-Pick disease, leaves the cell with no or limited or ability to degrade sphingomyelin. In a severe form (type A) of this disease, the liver and spleen are sites of lipid deposits and are therefore tremendously enlarged. The lipid deposits consist primarily of the sphingomyelin that cannot be degraded. See also Lipid metabolism.

>Glycerol esterified to two molecules of fatty acid, one of which is commonly polyunsaturated. The third hydroxyl group is esterified to phosphate and one of a number of water-soluble compounds, including serine (phosphatidylserine), ethanolamine (phosphatidylethanolamine), choline (phosphatidylcholine, also known as lecithin), and inositol (phosphatidylinositol).

Cell membranes are a double layer of phospholipids with the fatty acid side-chains on the inside and the water-soluble compound esterified to the phosphate interacts with water. This is why phospholipids can be used to emulsify oils and fats in water and are commonly used in food manufacture as emulsifiers.

From the energy point of view they can be regarded as being equivalent to simple fats (triacylglycerols); they also provide a dietary source of choline and inositol, neither of which is a dietary essential.

An organic compound made from a combination of glycerol, two fatty acids, and a phosphate group. Phospholipids are major components of all cell membranes. They are involved in the transport of fat in the blood and lymph, and also take part in many other metabolic reactions throughout the body.

An organic compound consisting of a hydrophobic tail of two chains of fatty acid, and a hydrophilic head of glycerol and phosphate. Phospholipid is a major component of all cell membranes, and is involved in fat transport in blood and lymph. Phospholipids are also involved in many metabolic reactions.

Any lipid that contains phosphorus, including those with a glycerol backbone (phosphoglycerides and plasmalogens) or a backbone of sphingosine or a related substance (sphingomyelins). They are the major lipids in cell membranes.

• p. bilayer — a layer containing two phospholipid molecules which is the basic structural unit of all biological membranes.

One of a class of compounds, widely distributed in living cells, containing phosphoric acid, fatty acids, and a nitrogenous base.

• Physiology - phospholipid: lipid compound containing water-soluble phosphate group

Phospholipid

The left image shows a phospholipid, and the right image shows the chemical makeup.

Phosphatidyl choline is the major component of lecithin. It is also a source for choline in the synthesis of acetylcholine in cholinergic neurons.

Cell membranes consist of phospholipid bilayers

Phospholipids are a class of lipids that are a major component of all cell membranes as they can form lipid bilayers. Most phospholipids contain a diglyceride, a phosphate group, and a simple organic molecule such as choline; one exception to this rule is sphingomyelin, which is derived from sphingosine instead of glycerol. The first phospholipid identified as such in biological tissues was lecithin, or phosphatidylcholine, in the egg yolk, by Theodore Nicolas Gobley, a French chemist and pharmacist, in 1847. The structure of the phospholipid molecule generally consists of hydrophobic tails and a hydrophilic head. It is usually found with cholesterol molecules which are found in-between the spaces of the phospholipid.

Contents 1 Amphipathic character 2 Types of phospholipid 2.1 Diacylglyceride structures 2.2 Phosphosphingolipids 3 Simulations 4 Characterization 5 Phospholipid synthesis 6 In signal transduction 7 Food technology 8 Phospholipid derivatives 9 Abbreviations used and chemical information of glycerophospholipids 10 See also 11 References

Amphipathic character

The 'head' is hydrophilic (attracted to water), while the hydrophobic 'tails' are repelled by water and are forced to aggregate. The hydrophillic head contains the negatively charged phosphate group, and may contain other polar groups. The hydrophobic tail usually consists of long fatty acid hydrocarbon chains. When placed in water, phospholipids form a variety of structures depending on the specific properties of the phospholipid. These specific properties allow phospholipids to play an important role in the phospholipid bilayer. In biological systems, the phospholipids often occur with other molecules (e.g., proteins, glycolipids, cholesterol) in a bilayer such as a cell membrane.^[1] Lipid bilayers occur when hydrophobic tails line up against one another, forming a membrane hydrophilic heads on both sides facing the water.

Such movement can be described by the Fluid Mosaic Model, that 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. Cholesterol contributes 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.

Types of phospholipid

Diacylglyceride structures

See: Glycerophospholipid

• Phosphatidic acid (phosphatidate) (PA)
• Phosphatidylethanolamine (cephalin) (PE)
• Phosphatidylcholine (lecithin) (PC)
• Phosphatidylserine (PS)
• Phosphoinositides:
  • Phosphatidylinositol (PI)
  • Phosphatidylinositol phosphate (PIP)
  • Phosphatidylinositol bisphosphate (PIP2) and
  • Phosphatidylinositol triphosphate (PIP3).

Phosphosphingolipids

• Ceramide phosphorylcholine (Sphingomyelin) (SPH)
• Ceramide phosphorylethanolamine (Sphingomyelin) (Cer-PE)
• Ceramide phosphorylglycerol

Simulations

Computational simulations of phospholipids are often performed using molecular dynamics with force fields such as GROMOS, CHARMM, or AMBER.

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 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.

Phospholipid synthesis

Phospholipid synthesis occurs in the cytosol adjacent to 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.^[2]

In signal transduction

Some types of phospholipid can be split to produce products that function as second messengers in signal transduction. Examples include phosphatidylinositol (4,5)-bisphosphate (PIP₂), that can be split by the enzyme Phospholipase C into inositol triphosphate (IP₃) and diacylglycerol (DAG), which both carry out the functions of the G_q type of G protein in response to various stimuli and intervene in various processes from long term depression in neurons^[3] to leukocyte signal pathways started by chemokine receptors.^[4]

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 similar in structure to prostaglandins that mediates defensive responses against pathogens.

Food technology

Phospholipids can act as an emulsifier, enabling oils to form a colloid with water. Phospholipids are one of the components of lecithin which is found in egg-yolks, as well as being extracted from soy beans, and is used as a food additive in many products, and can be purchased as a dietary supplement.

Phospholipid derivatives

See table below for an extensive list.

• Natural phospholipid derivates:

  egg PC, 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, funcitionalized-phospholipid, terminal activated-phospholipid)

Abbreviations used and chemical information of glycerophospholipids

Abbreviation	CAS	Name	Type
DDPC	3436-44-0	1,2-Didecanoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
DEPA-NA	80724-31-8	1,2-Dierucoyl-sn-glycero-3-phosphate (Sodium Salt)	Phosphatidic acid
DEPC	56649-39-9	1,2-Dierucoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
DEPE	988-07-2	1,2-Dierucoyl-sn-glycero-3-phosphoethanolamine	Phosphatidylethanolamine
DEPG-NA		1,2-Dierucoyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Sodium Salt)	Phosphatidylglycerol
DLOPC	998-06-1	1,2-Dilinoleoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
DLPA-NA		1,2-Dilauroyl-sn-glycero-3-phosphate (Sodium Salt)	Phosphatidic acid
DLPC	18194-25-7	1,2-Dilauroyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
DLPE		1,2-Dilauroyl-sn-glycero-3-phosphoethanolamine	Phosphatidylethanolamine
DLPG-NA		1,2-Dilauroyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Sodium Salt)	Phosphatidylglycerol
DLPG-NH4		1,2-Dilauroyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Ammonium Salt)	Phosphatidylglycerol
DLPS-NA		1,2-Dilauroyl-sn-glycero-3-phosphoserine (Sodium Salt)	Phosphatidylserine
DMPA-NA	80724-3	1,2-Dimyristoyl-sn-glycero-3-phosphate (Sodium Salt)	Phosphatidic acid
DMPC	18194-24-6	1,2-Dimyristoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
DMPE	988-07-2	1,2-Dimyristoyl-sn-glycero-3-phosphoethanolamine	Phosphatidylethanolamine
DMPG-NA	67232-80-8	1,2-Dimyristoyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Sodium Salt)	Phosphatidylglycerol
DMPG-NH4		1,2-Dimyristoyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Ammonium Salt)	Phosphatidylglycerol
DMPG-NH4/NA		1,2-Dimyristoyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Sodium/Ammonium Salt)	Phosphatidylglycerol
DMPS-NA		1,2-Dimyristoyl-sn-glycero-3-phosphoserine (Sodium Salt)	Phosphatidylserine
DOPA-NA		1,2-Dioleoyl-sn-glycero-3-phosphate (Sodium Salt)	Phosphatidic acid
DOPC	4235-95-4	1,2-Dioleoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
DOPE	4004-5-1-	1,2-Dioleoyl-sn-glycero-3-phosphoethanolamine	Phosphatidylethanolamine
DOPG-NA	62700-69-0	1,2-Dioleoyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Sodium Salt)	Phosphatidylglycerol
DOPS-NA	70614-14-1	1,2-Dioleoyl-sn-glycero-3-phosphoserine (Sodium Salt)	Phosphatidylserine
DPPA-NA	71065-87-7	1,2-Dipalmitoyl-sn-glycero-3-phosphate (Sodium Salt)	Phosphatidic acid
DPPC	63-89-8	1,2-Dipalmitoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
DPPE	923-61-5	1,2-Dipalmitoyl-sn-glycero-3-phosphoethanolamine	Phosphatidylethanolamine
DPPG-NA	67232-81-9	1,2-Dipalmitoyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Sodium Salt)	Phosphatidylglycerol
DPPG-NH4	73548-70-6	1,2-Dipalmitoyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Ammonium Salt)	Phosphatidylglycerol
DPPS-NA		1,2-Dipalmitoyl-sn-glycero-3-phosphoserine (Sodium Salt)	Phosphatidylserine
DSPA-NA	108321-18-2	1,2-Distearoyl-sn-glycero-3-phosphate (Sodium Salt)	Phosphatidic acid
DSPC	816-94-4	1,2-Distearoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
DSPE	1069-79-0	1,2-Distearoyl-sn-glycero-3-phosphoethanolamine	Phosphatidylethanolamine
DSPG-NA	67232-82-0	1,2-Distearoyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Sodium Salt)	Phosphatidylglycerol
DSPG-NH4	108347-80-4	1,2-Distearoyl-sn-glycero-3[Phospho-rac-(1-glycerol...) (Ammonium Salt)	Phosphatidylglycerol
DSPS-NA		1,2-Distearoyl-sn-glycero-3-phosphoserine (Sodium Salt)	Phosphatidylserine
Egg Sphingomyelin empty Liposome
EPC		Egg-PC	Phosphatidylcholine
HEPC		Hydrogenated Egg PC	Phosphatidylcholine
HSPC		High purity Hydrogenated Soy PC	Phosphatidylcholine
HSPC		Hydrogenated Soy PC	Phosphatidylcholine
LYSOPC MYRISTIC	18194-24-6	1-Myristoyl-sn-glycero-3-phosphocholine	Lysophosphatidylcholine
LYSOPC PALMITIC	17364-16-8	1-Palmitoyl-sn-glycero-3-phosphocholine	Lysophosphatidylcholine
LYSOPC STEARIC	19420-57-6	1-Stearoyl-sn-glycero-3-phosphocholine	Lysophosphatidylcholine
Milk Sphingomyelin MPPC		1-Myristoyl-2-palmitoyl-sn-glycero 3-phosphocholine	Phosphatidylcholine
MSPC		1-Myristoyl-2-stearoyl-sn-glycero-3–phosphocholine	Phosphatidylcholine
PMPC		1-Palmitoyl-2-myristoyl-sn-glycero-3–phosphocholine	Phosphatidylcholine
POPC	26853-31-6	1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
POPE		1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine	Phosphatidylethanolamine
POPG-NA	81490-05-3	1-Palmitoyl-2-oleoyl-sn-glycero-3[Phospho-rac-(1-glycerol)...] (Sodium Salt)	Phosphatidylglycerol
PSPC		1-Palmitoyl-2-stearoyl-sn-glycero-3–phosphocholine	Phosphatidylcholine
SMPC		1-Stearoyl-2-myristoyl-sn-glycero-3–phosphocholine	Phosphatidylcholine
SOPC		1-Stearoyl-2-oleoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine
SPPC		1-Stearoyl-2-palmitoyl-sn-glycero-3-phosphocholine	Phosphatidylcholine

See also

• Galactolipid
• Sulfolipid
• Cable theory

References

1. ^ Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. http://www.phschool.com/el_marketing.html. 
2. ^ Lodish, Harvey; Berk, Krieger, Kaiser, Scott, Bretsher, Ploegh, Matsuaira (2008). Molecular Cell Biology. W.H. Freeman and Company. ISBN 0-7167-7601-4. http://bcs.whfreeman.com/lodish6e/default.asp?s=&n=&i=&v=&o=&ns=0&uid=0&rau=0. 
3. ^ Se-Young Choi et al (2005). "Multiple Receptors Coupled to Phospholipase C Gate Long-Term Depression in Visual Cortex". The Journal of Neuroscience. 
4. ^ Darran G. Cronshaw et al (2006). "Evidence that phospholipase C-dependent, calcium-independent mechanisms are required for directional migration of T lymphocytes in response to the CCR4 ligands CCL17 and CCL22". Journal of Leukocyte Biology 79. 

v t e Structures of the cell membrane Membrane lipids Lipid bilayer Phospholipids Proteolipids Sphingolipids Sterols Membrane protein locations Membrane glycoproteins Integral membrane proteins/transmembrane protein Peripheral membrane protein/Lipid-anchored protein Other Caveolae/Coated pits Cell junctions Glycocalyx Lipid raft/microdomains Membrane contact sites Membrane nanotubes Myelin sheath Nodes of Ranvier Nuclear envelope Phycobilisomes Porosomes B memb: cead, trns (1A, 1C, 1F, 2A, 3A1, 3A2-3, 3D), othr

v t e Lipids: phospholipids Glycerol backbone (Glycerophospholipids/ Phosphoglycerides) Phosphatidyl-: -ethanolamine/cephalin (PE) · -choline/lechithin (PC) · -serine (PS) · -glycerol (PG) · -inositol (PI) (glyco- (GPI)) Phosphoinositides: PIP (PI(3)P, PI(4)P, PI(5)P) · PIP2 (PI(3,4)P2, PI(3,5)P2, PI(4,5)P2) · PIP3 Cardiolipin Ether lipids: Plasmalogen (Platelet-activating factor) Sphingosine backbone Sphingomyelin Metabolites Inositol phosphate · Inositol Lysophosphatidic acid Choline · Phosphocholine · Citicoline M: MET mt, k, c/g/r/p/y/i, f/h/s/l/o/e, a/u, n, m k, cgrp/y/i, f/h/s/l/o/e, au, n, m, epon m(A16/C10),i(k, c/g/r/p/y/i, f/h/s/o/e, a/u, n, m) biochemical families: proteins (amino acids/intermediates) · nucleic acids (constituents/intermediates) · carbohydrates (glycoproteins, alcohols, glycosides) lipids (fatty acids/intermediates, phospholipids, steroids, sphingolipids, eicosanoids) · tetrapyrroles/intermediates

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