Chemistry
Phospholipid
Phospholipids are a class of lipids that are essential components of cell membranes. They consist of a hydrophilic head and two hydrophobic tails, making them amphipathic. This unique structure allows phospholipids to form lipid bilayers, which serve as the foundation of cell membranes and play a crucial role in maintaining cellular integrity and function.
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10 Key excerpts on "Phospholipid"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Research World(Publisher)
Of the Phospholipids, the most common headgroup is phosphatidylcholine (PC), accounting for about half the Phospholipids in most mammalian cells. PC is a zwitterionic headgroup, as it has a negative charge on the phosphate group and a positive charge on the amine but, because these local charges balance, no net charge. Other headgroups are also present to varying degrees and can include phosphatidylserine (PS) phosphatidylethanolamine (PE) and phosphatidylglycerol (PG). These alternate headgroups often confer specific biological functionality that is highly context-dependent. For instance, PS presence on the extracellular membrane face of erythrocytes is a marker of cell apoptosis, whereas PS in growth plate vesicles is necessary for the nucleation of hydroxyapatite crystals and subsequent bone mineralization. Unlike PC, some of the other headgroups carry a net charge, which can alter the electrostatic interactions of small molecules with the bilayer. Biological roles Containment and separation The primary role of the lipid bilayer in biology is to separate aqueous compartments from their surroundings. Without some form of barrier delineating “self” from “non-self” it is difficult to even define the concept of an organism or of life. This barrier takes the form of a lipid bilayer in all known life forms except for a few species of archaea which utilize a specially adapted lipid monolayer. 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. The partitioning ability of the lipid bilayer is based on the fact that hydrophilic molecules cannot easily cross the hydrophobic bilayer core, as discussed in Transport across the bilayer below. Prokaryotes have only one lipid bilayer- the cell membrane (also known as the plasma membrane).
eBook - PDFLung Surfactants
Basic Science and Clinical Applications
- Robert H. Notter(Author)
- 2000(Publication Date)
- CRC Press(Publisher)
Additional biological roles of Phospholipids range from participating in cell membane signaling to serving as substrates for metabolism. Less widely appreciated, but certainly as crucial, is the activity of Phospholipids as constitu-45 3 Phospholipids: Introduction to Structure and Biophysics ents of lung surfactant. Phospholipids make up approximately 85% of endoge-nous lung surfactant by weight [365, 568, 569, 936, 1105], and they are also major constituents of most clinical exogenous surfactants. The molecular structure and biophysical behavior of Phospholipids are directly linked to their surface active function in lung surfactants ( Chapter 8 ). III. Phospholipid Classes and Their Molecular Structure With the exception of lyso-derivatives, glyceroPhospholipids have a molecular structure containing a polar headgroup and two nonpolar fatty acyl chains ( Figure 3-1 ) [22, 301, 1007]. GlyceroPhospholipid classes are defined by the structure of the headgroup attached via a phosphate moiety (PO 4 ) to the three-carbon glycerol backbone. The carbon atom to which the headgroup is attached is designated as number 3 ( sn -3 in stereospecific numbering). The acyl chains of Phospholipids are attached by ester linkages to carbons 1 and 2 ( sn -1 and sn -2) in the glycerol backbone. These fatty chains vary in length and saturation (number of double bonds) and strongly affect molecular behavior. Glycero-Phospholipid classes shown in Figure 3-1 are phosphatidylcholine (PC), phos-phatidylethanolamine (PE), phosphatidylglycerol (PG), phosphatidylinositol (PI), and phosphatidylserine (PS).
eBook - PDFFood Lipids
Chemistry, Nutrition, and Biotechnology, Fourth Edition
- Casimir C. Akoh(Author)
- 2017(Publication Date)
- CRC Press(Publisher)
Sugar attached to protein Sugar attached to lipid Phospholipid bilayer Protein Cholesterol Protein FIGURE 2.6 Graphical representation of a biological membrane. (From Brown, B.S., Biological mem- branes, The Biochemical Society, http://www.biochemistry.org/portals/0/education/docs/basc08_full.pdf, 1996, accessed October 10, 2016.) 50 Food Lipids: Chemistry, Nutrition, and Biotechnology are covalently linked to some of the lipids and proteins within the membranes. Different lipids have specific functions in the membrane as their structure will determine the molecular organization influencing membrane fluidity [4]. The most common Phospholipids, known as glyceroPhospholipids, are based on a glycerol backbone. GlyceroPhospholipids can be subdivided into distinct classes, based on the nature of the polar head group at the sn-3 position of the glycerol backbone in eukaryotes and eubacteria or the sn-1 position in the case of archaebacteria. Accordingly, the different classes of glycerophos- pholipids are phosphatidylcholine (PC; Figure 2.7a), phosphatidylethanolamine (PE; Figure 2.7b), phosphatidylserine (PS; Figure 2.7c), phosphatidylglycerol (PG; Figure 2.7d), phosphatidylinositol (PI; Figure 2.7e), and phosphatidic acid (PA; Figure 2.7f). If the sn-1 position (R 1 in Figure 2.7) is hydrolyzed, the corresponding lysoPhospholipid is formed. A second glycerol unit constitutes part of the head group in the glycerophosphoglycerols (PG; Figure 2.7d) and glycerophosphoglyc- erophosphates (Figure 2.8), whereas for the glycerophosphoglycerophosphoglycerols (cardiolipins; Figure 2.8), a third glycerol unit is typically acylated at the sn-1 ′ and sn-2′ positions to create a pseudo-symmetrical molecule. VI. PHYSICAL PROPERTIES OF PhospholipidS The packing behavior of lipids is determined by the intermolecular repulsive and attractive forces of the polar head group of the lipid [53].
eBook - PDFHandbook of Food Analysis
Volume 1: Physical Characterization and Nutrient Analysis
- Leo M.L. Nollet(Author)
- 2004(Publication Date)
- CRC Press(Publisher)
12 Phospholipids Bert Vanhoutte, Roeland Rombaut, Paul Van der Meeren, and Koen Dewettinck Faculty of Agricultural and Applied Biological Sciences, Ghent University, Ghent, Belgium I. INTRODUCTION Phospholipids (PL) are amphiphilic molecules with lipophilic acyl chains and a hydrophilic head. Gene-rally, two main types of Phospholipids can be found in living tissues. A first group, the glyceroPhospholipids, consist of a glycerol backbone with two fatty acids esterified at position sn-1 or sn-2. On the third hydroxyl, a phos-phate residue is bound on to which different organic bases or other complex organic groups may be linked. Generally, the fatty acid chain on the sn-1 position is more saturated compared to the one at the sn-2 position on the glycerol moiety. LysoPhospholipids (LPC, LPE, etc.) contain only one acyl group, which is predominantly esterified at the sn-1 position. Apart from diacyl forms, some Phospholipid species from animal and microbial origin have an ether or vinyl ether linkage at the sn-1 position, and are denoted as alkylacyl-and alkenylacyl-glyceroPhospholipids, respectively. The latter form is also known as plasma-logen. The polar organic base on the phosphate determines the type of Phospholipid. Phosphatidic acid (PA) is an important intermediate in the biosynth-esis of triglycerides and Phospholipids; however, it is only present in very small amounts in living tissue. The concentration of this acidic Phospholipid is often overestimated due to enzymatic hydrolysis of other Phospholipids by phospholipase D. Phosphatidylgly-cerol (PG) is present in the mitochondria of bacteria and in chloroplasts of plants. In animal tissues it serves as an intermediate for diphosphatidylglycerol or cardiolipin , which plays a role in oxidative stress and aging phenomena. With values up to 50% of total PL the most abundant Phospholipid in animal and plant membrane material is undoubtedly phosphatidylcho-line (PC) or lecithin .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Research World(Publisher)
Because lipid bilayers are quite fragile and are so thin that they are invisible in a traditional microscope, bilayers are very challenging to study. ________________________ WORLD TECHNOLOGIES ________________________ Experiments on bilayers often require advanced techniques like electron microscopy and atomic force microscopy. Phospholipids with certain head groups can alter the surface chemistry of a bilayer and can, for example, mark a cell for destruction by the immune system. Lipid tails can also affect membrane properties, for instance by determining the phase of the bilayer. The bilayer can adopt a solid gel phase state at lower temperatures but undergo phase transition to a fluid state at higher temperatures. The packing of lipids within the bilayer also affects its mechanical properties, including its resistance to stretching and bending. Many of these properties have been studied with the use of artificial model bilayers produced in a lab. Vesicles made by model bilayers have also been used clinically to deliver drugs. Biological membranes typically include several types of lipids other than Phospholipids. A particularly important example in animal cells is cholesterol, which helps strengthen the bilayer and decrease its permeability. Cholesterol also helps regulate the activity of certain integral membrane proteins. Integral membrane proteins function when incorporated into a lipid bilayer. Because bilayers define the boundaries of the cell and its compartments, these membrane proteins are involved in many intra- and inter-cellular signaling processes. Certain kinds of membrane proteins are involved in the process of fusing two bilayers together. This fusion allows the joining of two distinct structures as in the fertilization of an egg by sperm or the entry of a virus into a cell. The three main structures Phospholipids form in solution; the liposome (a closed bilayer), the micelle and the bilayer.
eBook - PDF- Leo M.L. Nollet, Fidel Toldra(Authors)
- 2012(Publication Date)
- CRC Press(Publisher)
Phospholipids have therapeutic properties, and they were used to improve human physiological and mental performance, lowering cho-lesterol levels, and treating neurological disorders (Hidalgo and Zamora, 2006). PC is significant as a nerve cell membrane material as well as a supplier of choline, which suggests it may improve memory in memory-deficient mice (Chung et al., 1995; Moriyama et al., 1996). Recent research has introduced Phospholipids as a novel class of plant growth regulators (Cowan, 2006). Furthermore, Phospholipids have large industrial applications in food and nutraceuticals, cosmet-ics, agricultural products, and pharmaceuticals (Song, et al., 2005). They are used mainly as nontoxic biodegradable emulsifiers, industrial lubricants, and nutrition supplements (Hamama and Bhardwaj, 2004). In contrast to other Phospholipids species, glyceroPhospholipids have been widely used in foods and other industrial fields (Guo et al., 2005b). R 2 C O O CH CH 2 CH 2 O C O R 1 O P O OH O Na R 2 C O O CH CH 2 CH 2 O C O R 1 O P O O O NH 4 CH 2 CH OH CH 2 OH R 2 C O O CH CH 2 CH 2 O C O R 1 O P O O O CH 2 CH 2 N(CH 3 ) 3 R 2 C O O CH CH 2 CH 2 O C O R 1 O P O O O CH 2 CH 2 NH 3 R 2 C O O CH CH 2 CH 2 O C O R 1 O P O O O CH 2 CH NH 3 C O OH R 2 C O O CH CH 2 CH 2 O C O R 1 O P O O O OH OH OH HO OH Na Phosphatidic acid Phosphatidic glycerol Phosphatidic choline Phosphatidyl ethanolamine Phosphatidyl serine Phosphatidyl inositol + + – – + – + – + – + – FIGURE 6.1 Molecular structure of glyceroPhospholipid classes. 221 Phospholipids 6.2 Occurrence of Phospholipids Phospholipids are naturally occurring lipids found in all organisms (Song et al., 2005). GlyceroPhospholipids are ubiquitous from eukaryotes, such as mammals, plants, and yeasts, to prokaryotes.
- Dennis E. Vance, J.E. Vance(Authors)
- 1996(Publication Date)
- Elsevier Science(Publisher)
Roles of individual lipid components may therefore relate to establishing appropriate permeability characteristics, satisfying insertion and packing requirements in the region of integral proteins (which penetrate into or through the bilayer), as well as allowing the surface association of peripheral proteins via electrostatic interactions. All these demands are clearly critical. An intact permeability barrier to small ions such as Na +, K +, and H +, for example, is vital for establishing the electrochemical gradients which give rise to a membrane potential and drive other membrane-mediated transport processes. In addition, the lipid in the region of membrane protein must seal the protein into the bilayer so that non-specific leakage is prevented and an environment appropriate to a functional protein conformation is provided. More extended discussions of biomembranes and the roles of lipids can be found in the excellent text by Gennis [3]. 2 Lipid diversity and distribution The general definition of a lipid is a biological material soluble in organic solvents, such as ether or chloroform. Here we discuss the diverse chemistry of the sub-class of lipids which are found in membranes. This excludes other lipids which are poorly soluble in bilayer membrane systems, such as triacylglycerols and cholesteryl esters. 2.1 Chemical diversity of lipids The major classes of lipids found in biological membranes are summarized in Fig. 2. In eukaryotic membranes the glycerol-based Phospholipids are predominant, including phosphatidylcholine PC, phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI) and cardiolipin. Sphingosine-based lipids, including sphingomyelin and the glycosphingolipids, also constitute a major fraction. The glycolipids, which can also include carbohydrate-containing glycerol-based lipids (found particularly in plants), play major roles as cell-surface-associated antigens and recognition factors in eukaryotes (Chapter 12)
No longer available |Learn more- (Author)
- 2014(Publication Date)
- College Publishing House(Publisher)
Because lipid bilayers are quite fragile and are so thin that they are invisible in a traditional microscope, bilayers are very challenging to study. Experiments on bilayers often require advanced techniques like electron microscopy and atomic force microscopy. ________________________ WORLD TECHNOLOGIES ________________________ Phospholipids with certain head groups can alter the surface chemistry of a bilayer and can, for example, mark a cell for destruction by the immune system. Lipid tails can also affect membrane properties, for instance by determining the phase of the bilayer. The bilayer can adopt a solid gel phase state at lower temperatures but undergo phase transition to a fluid state at higher temperatures. The packing of lipids within the bilayer also affects its mechanical properties, including its resistance to stretching and bending. Many of these properties have been studied with the use of artificial model bilayers produced in a lab. Vesicles made by model bilayers have also been used clinically to deliver drugs. Biological membranes typically include several types of lipids other than Phospholipids. A particularly important example in animal cells is cholesterol, which helps strengthen the bilayer and decrease its permeability. Cholesterol also helps regulate the activity of certain integral membrane proteins. Integral membrane proteins function when incorporated into a lipid bilayer. Because bilayers define the boundaries of the cell and its compartments, these membrane proteins are involved in many intra- and inter-cellular signaling processes. Certain kinds of membrane proteins are involved in the process of fusing two bilayers together. This fusion allows the joining of two distinct structures as in the fertilization of an egg by sperm or the entry of a virus into a cell. The three main structures Phospholipids form in solution; the liposome (a closed bilayer), the micelle and the bilayer.
eBook - PDF- A.G. Lee(Author)
- 1995(Publication Date)
- Elsevier Science(Publisher)
This review will serve to summarize and update earlier treatments, and thus some familiarity with the different structures and classes of lipids, the common types of model membrane systems and the techniques by which they are formed, and the basic physical properties of bilayers is assumed. This review will focus on lipid polymorphism and its relation to membrane fusion, and the role of membrane order in growth and protein function. II. LIPID DIVERSITY The main classes of lipids found in eukaryotic biological membranes include the glyceroPhospholipids, the sphingolipids, and cholesterol (Chol) (Cullis and Hope, 1991). Of the former group, phosphatidylcholine (PC) is the major lipid, but phosphatidylethanolamine (PE), phosphatidylserine (PS), phosphatidylinositol (PI), and cardiolipin (CL) are also major lipid species in biological membranes. A representative chemical structure of a common Phospholipid, 1-palmitoyl-2- Roles of Lipids in Biological Membranes 3 O II § -O~ P ~O~CH2~CH2~ N(CH3) 3 I O I O O OH HC~ CH I CH A O II -O~P~O~CH2~CH2~ I O I CH~CH NH B + N(CH3) 3 Figure 1. Chemical structures of representative Phospholipids POPC (A) and SPM (B). oleoyl-sn-glycero-3-phosphocholine (POPC), is shown in Figure 1A. The sphin- golipids include sphingomyelin (SPM), ceramide (CER), and the glycosphin- golipids (GSLs). The structure of SPM is shown in Figure 1B, where its similarity with PC is apparent. CER is a SPM molecule in which the phosphocholine headgroup has been replaced with a hydroxyl group; the GSLs contain carbohydrate headgroups where the number of sugar residues can range from one, in the glucosyl- and galactosylceramides, to five in the more complex lipids such as ganglioside GM1 (GM1). In procaryotic membranes, the major Phospholipids are PE, phosphatidylglycerol (PG), and CL; PC is not usually present (Gurr and Harwood, 1991).
eBook - PDF- Adam Baszkin, Willem Norde(Authors)
- 1999(Publication Date)
- CRC Press(Publisher)
It must therefore be kept in mind that, while great biological diversity in the membrane lipid composition is not unexpected, the observed differences may vary from one experimental setup to another. Various cells also have a different "buffering" or "resistance" capacity to the induced change in the membrane lipid composition. Normally, a cell will change its lipid metabolism and membrane composition depending on the requirement for specific membrane organization and dynamism; proteins associated with or incorporated in the lipid membrane environment will par- ticipate in the process. Current evidence suggests that genetic as well as environmental factors play a role in this, in as yet unknown proportions, and that cell-to-cell varia- bility is appreciable. The ability to manipulate the lipid membrane composition and thereby to modifY the cell function offers a means of studying the role lipids play in nature. This capability also opens ways for medical approaches that can be referred to as membrane-lipid replacement therapy. In every instance, such manipulations have a chance for success only if the structure and the properties of the membrane as a whole are properly understood. REFERENCES Abrahamsson S, Dahlen B, Lofgren H, Pascher I, Sundell S. In: Abrahamsson S, and Pascher I, eds. Structure of Biological Membranes: New York: Plenum, 1977, pI. Ansell GB, Hawthorne JN, Dawson RMC. Historical introduction. In: Ansell GB, Hawthorne JW, Dawson RMC, eds. Form and Function of Phospholipids. Amsterdam: Elsevier, 1973, p 1-8. Aranda-Espinoza H, Berman A, Dan N, Pincus P, Safran S. Interaction between inclusions embedded in membranes. Biophys J 71:648-656, 1996. Bangham AD. Liposomes-The Babraham connection. Chern Phys Lipids 64:275-285, 1993. Bangham AD, Hill MW, MillerWGA Preparation and use ofliposomes as models ofbiological membranes. Methods Membr Bioll:1-68, 1974. Bar LK, Barenholz Y, Thompson TE.
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