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From Wikipedia, the free encyclopedia

 Phospholipid
Phospholipid
 The left image shows a phospholipid, and the right image shows the chemical makeup.
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.
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
Cell membranes consist of phospholipid bilayers

Phospholipids are a class of lipids that are a major component of all cell membranes. They can form lipid bilayers because of their amphiphilic characteristic. The structure of the phospholipid molecule generally consists of two hydrophobic fatty acid "tails" and a hydrophilic "head" consisting of a phosphate group. The two components are joined together by a glycerol molecule. The phosphate groups can be modified with simple organic molecules such as choline.

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. Biological membranes in eukaryotes also contain another class of lipid, sterol, interspersed among the phospholipids and together they provide membrane fluidity and mechanical strength. Purified phospholipids are produced commercially and have found applications in nanotechnology and materials science.[1]

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Transcription

In this video, we're going to actually explore in detail the structure of phospholipids in our cell membrane. Just to briefly remind us, our phospholipid is often drawn like this. It has that polar phosphate head group, and it has two fatty acid chains. And all of this is held together by glycerol backbone. But what does that really mean? What dose is picture actually look like down to a molecule? Well, let's talk about the first one, the fatty acid. And just to remind us, there are actually two fatty acids-- times 2. You can see that there are two tails hanging down here. So our fatty acid is basically a carboxylic acid attached to a very long carbon chain. And so our carboxylic acid is like this. It has a double bonded O and a hydroxyl group. And it has that really long carbon chain which we're just going to call an R-group. The next one is our glycerol backbone, and glycerol is a pretty basic structure. It looks like this. It has three carbons attached to three hydroxyl groups-- three alcohol groups. And there's only one glycerol in each phospholipid. a The last one is our phosphate group, that big polar head group that we talk about. And just like you would think, there's a phosphorus in a phosphate group, and there are four oxygens attached to it. Now, what does this actually look like all put together? Just for the sake of time, I've pre-drawn a picture of all this put together. It looks like this. So you can see that we have our two fatty acid chains attached through an ester bond with our glycerol attached through another ester bond with our phosphate group. Now, you'll notice that one of the negative oxygens is missing, and it's been replaced with a hydroxyl group-- an alcohol group. And that's what this is in the orange. Well, that's because in our cell, a phospholipid actually looks like this. The negative oxygen actually picks up the hydrogen and becomes an alcohol group. Now, a phospholipid molecule that looks like this is actually pretty rare in our cell membrane, and the reason why is because phospholipids can occur. And the reason why is because this molecule could actually bond with several different molecules, giving a really diverse set of phospholipids. And again, for the sake of time, I've pre-drawn these molecules, and unless you're a researcher who really, really loves the cell membrane, you probably won't need to know this by heart, because these structures get a little complicated. But it's still good idea to get acquainted to what they kind of look like. So there's serine, choline, ethanolomine, inositol, and glycerol. And you'll notice that I've also drawn these particular special hydroxyl groups in orange, and the reason why is because these hydroxyl groups in orange, from serine, choline, and so on, can actually bond to our phosphate group through what we call a phosphoester bond. Now, what would this actually look like in a real molecule? What would it look like if serine actually bonded with this phospholipid? Well, we're going to transition briefly into another slide, just because I'm running out of space. And you'll notice that there are five different phospholipids that they can actually occur. There's phosphatidylserine, phosphatidylcholine, phosphatidtylethanolomine, phosphatidylinositol, and diphosphatidylgylcerol, also known as cardiolipin. And you'll notice that in this last one, there are actually two phosphatidyl p groups that actually bond to a middle gylcerol. And again, unless you're someone who really researches the cell membrane, you probably don't need to know these structures by heart, but what we do need to know is that the phospholipids in our cell membrane are actually very, very diverse, and there are several different forms they can take. So if we were to take a look in detail at the phospholipids that make up our cell membrane, we would actually find all of these scattered throughout the membrane. Now, we're just going to go back to our original picture. Just to remind us, this is again our nonpolar side, and this side in the yellow is polar. And so if we were to match up our general picture of a phospholipid to the picture that we've drawn here, it would actually look like this. This is our polar head group, and we have two fatty acids here. And again, you'll notice that the glycerol group isn't really drawn in, because that's what holds everything together. And just to wrap up, we need to talk about one brief thing. So we have our phospholipids like this. Now, this so-called R-group is made up of a really long chain of carbons. Now, in many cases, these carbons can actually form double bonds with each other, like a lot of different carbons do. And remember that double bonds occur in the form of cis and occur in the form of trans. So a cis bond in chemistry is when we have a double bonded carbon and we have the carbons on each side being on the same side, while in the trans bond, our carbons are on opposite sides. Again, these are hydrogens. And if we were to zoom out of this detailed molecule, in the case of trans, our fatty acid would just be pretty straight, like that. But in the case of cis, we can actually create a kink, because this bend from our cis bond actually gives it a kink. And this actually has a lot of significance when we talk about the fluidity of a cell membrane. So in summary, our phospholipids are made up of three major things-- fatty acids, glycerol, and phosphate. And these three things actually looks like this if we were to draw out a detailed molecule. And not only so, but there's an OH group on this polar phosphate group that actually can bond with several different types of molecules, producing a really, really diverse set of phospholipids that make up our cell membrane.

Contents

Amphiphilic character

An amphiphile (from the Greek αμφις, amphis: both and φιλíα, philia: love, friendship) is a term describing a chemical compound possessing both hydrophilic (water-loving, polar) and lipophilic (fat-loving) properties. The phospholipid head contains a negatively charged phosphate group and glycerol; it is hydrophilic (attracted to water). The phospholipid tails usually consists of 2 long fatty acid chains; they are hydrophobic and avoid interactions with water. When placed in aqueous solutions, phospholipids are driven by hydrophobic interactions that result in the fatty acid tails aggregating to minimize interactions with water molecules. 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, sterols) in a bilayer such as a cell membrane.[2] Lipid bilayers occur when hydrophobic tails line up against one another, forming a membrane of 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. Sterols 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.[citation needed]

Diacylglyceride structures

See: Glycerophospholipid

Phosphosphingolipids

See Sphingolipid

  • 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 properties. The ethosomal formulation of ketoconazole using phospholipids is a promising option for transdermal delivery in fungal infections.[3]

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.

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 nuclear magnetic resonance spectroscopy (NMR), particularly 31P-NMR,[4][5] while HPLC-ELSD[6] provides relative values.

Phospholipid synthesis

Phospholipid synthesis occurs in the cytosole 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.[7][8]

Sources

Common sources of industrially produced phospholipids are soya, rapeseed, sunflower, chicken eggs, bovine milk, fish eggs etc. Each source has a unique profile of individual phospholipid species 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. 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 Gq type of G protein in response to various stimuli and intervene in various processes from long term depression in neurons[9] to leukocyte signal pathways started by chemokine receptors.[10]

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 emulsifiers, 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. 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.

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 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

References

  1. ^ Mashaghi S.; Jadidi T.; Koenderink G.; Mashaghi A. (2013). "Lipid Nanotechnology". Int. J. Mol. Sci. 14: 4242–4282. doi:10.3390/ijms14024242. PMC 3588097Freely accessible. PMID 23429269. 
  2. ^ Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall. ISBN 0-13-250882-6. [page needed]
  3. ^ Ketoconazole Encapsulated Liposome and Ethosome: GUNJAN TIWARI
  4. ^ N. Culeddu; M. Bosco; R. Toffanin & P. Pollesello (1998). "High resolution 31P NMR of extracted phospholipids". Magnetic Resonance in Chemistry. 36: 907–912. doi:10.1002/(sici)1097-458x(199812)36:12<907::aid-omr394>3.0.co;2-5. 
  5. ^ Furse, Samuel; Liddell, Susan; Ortori, Catharine A.; Williams, Huw; Neylon, D. Cameron; Scott, David J.; Barrett, David A.; Gray, David A. (2013). "The lipidome and proteome of oil bodies from Helianthus annuus (common sunflower)". Journal of Chemical Biology. 6 (2): 63–76. doi:10.1007/s12154-012-0090-1. PMC 3606697Freely accessible. PMID 23532185. 
  6. ^ T.L. Mounts; A.M. Nash (1990). "HPLC analysis of phospholipids in crude oil for evaluation of soybean deterioration". Journal of the American Oil Chemists' Society. 67 (11): 757–760. doi:10.1007/BF02540486. 
  7. ^ Lodish H, Berk A, et al. (2007). Molecular Cell Biology (6th ed.). W. H. Freeman. ISBN 0-7167-7601-4. 
  8. ^ Zheng, Lei (2016). "Biogenesis, transport and remodeling of lysophospholipids in Gram-negative bacteria". Biochimica et Biophysica Acta. doi:10.1016/j.bbalip.2016.11.015. 
  9. ^ Choi, S.-Y.; Chang, J; Jiang, B; Seol, GH; Min, SS; Han, JS; Shin, HS; Gallagher, M; Kirkwood, A (2005). "Multiple Receptors Coupled to Phospholipase C Gate Long-Term Depression in Visual Cortex". Journal of Neuroscience. 25 (49): 11433–43. doi:10.1523/JNEUROSCI.4084-05.2005. PMID 16339037. 
  10. ^ Cronshaw, D. G.; Kouroumalis, A; Parry, R; Webb, A; Brown, Z; Ward, SG (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 (6): 1369–80. doi:10.1189/jlb.0106035. PMID 16614259. 
This page was last edited on 12 November 2017, at 21:53.
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