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28-445: Thromboplastin ( TPL ) is derived from cell membranes and is a mixture of both phospholipids and tissue factor , neither of which are enzymes. Thromboplastin acts on and accelerates the activity of Factor Xa, also known as thrombokinase, aiding blood coagulation through catalyzing the conversion of prothrombin to thrombin . Thromboplastin is found in brain, lung, and other tissues and especially in blood platelets. Thromboplastin

56-413: A class of lectins found on the surface of leukocytes and endothelial cells bind to the carbohydrates attached to glycolipids to initiate the immune response. This binding causes leukocytes to leave circulation and congregate near the site of inflammation. This is the initial binding mechanism, which is followed by the expression of integrins which form stronger bonds and allow leukocytes to migrate toward

84-444: A glycolipid is the presence of a monosaccharide or oligosaccharide bound to a lipid moiety . The most common lipids in cellular membranes are glycerolipids and sphingolipids , which have glycerol or a sphingosine backbones, respectively. Fatty acids are connected to this backbone, so that the lipid as a whole has a polar head and a non-polar tail. The lipid bilayer of the cell membrane consists of two layers of lipids, with

112-408: A glycoside hydrolase enzyme. Sphingolipidoses are typically inherited, and their effects depend on which enzyme is affected, and the degree of impairment. One notable example is Niemann–Pick disease which can cause pain and damage to neural networks. The main function of glycolipids in the body is to serve as recognition sites for cell–cell interactions. The saccharide of the glycolipid will bind to

140-537: A key component. Currently, recombinant tissue factor is available and used in some PT assays. Placental derivatives are still available and are used in some laboratories. Phospholipid is available as an independent reagent or in combination with tissue factor as thromboplastin. Complete thromboplastin consists of tissue factor, phospholipids (since platelets were removed from blood sample being tested), and CaCl 2 to reintroduce calcium ions which were chelated by sodium citrate originally used to prevent coagulation of

168-454: A specific complementary carbohydrate or to a lectin (carbohydrate-binding protein), of a neighboring cell. The interaction of these cell surface markers is the basis of cell recognitions, and initiates cellular responses that contribute to activities such as regulation, growth, and apoptosis . An example of how glycolipids function within the body is the interaction between leukocytes and endothelial cells during inflammation. Selectins ,

196-401: A unique profile of individual phospholipid species, as well as fatty acids, and consequently differing applications in food, nutrition, pharmaceuticals, cosmetics, and drug delivery. Some types of phospholipid can be split to produce products that function as second messengers in signal transduction . Examples include phosphatidylinositol (4,5)-bisphosphate (PIP 2 ), that can be split by

224-418: Is a promising option for transdermal delivery in fungal infections. Advances in phospholipid research lead to exploring these biomolecules and their conformations using lipidomics . Computational simulations of phospholipids are often performed using molecular dynamics with force fields such as GROMOS , CHARMM , or AMBER . Phospholipids are optically highly birefringent , i.e. their refractive index

252-874: 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. 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 P-NMR , while HPLC - ELSD provides relative values. Phospholipid synthesis occurs in

280-403: Is found in egg yolks, as well as being extracted from soybeans , 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 . Glycolipid Glycolipids are lipids with a carbohydrate attached by a glycosidic (covalent) bond . Their role

308-425: Is just phospholipids, and not tissue factor. Therefore, although the coagulation cascade can be triggered in vitro through the intrinsic pathway only, in vivo coagulation is triggered by the extrinsic pathway. However, the model better describing how coagulation works is the so-called cell-based model, a more integrated picture of the whole process, in which phospholipid surfaces, such as those provided by platelets, are

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336-399: Is sometimes used as a synonym for the protein tissue factor (with its official name "Coagulation factor III [thromboplastin, tissue factor]"). Historically, thromboplastin was a lab reagent , usually derived from placental sources, used to assay prothrombin times (PT). When manipulated in the laboratory, a derivative could be created called partial thromboplastin. Partial thromboplastin

364-406: Is to maintain the stability of the cell membrane and to facilitate cellular recognition, which is crucial to the immune response and in the connections that allow cells to connect to one another to form tissues . Glycolipids are found on the surface of all eukaryotic cell membranes, where they extend from the phospholipid bilayer into the extracellular environment. The essential feature of

392-427: The fluid mosaic model , 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. Sterols contribute to membrane fluidity by hindering the packing together of phospholipids. However, this model has now been superseded, as through

420-405: The breakage of glycosidic bonds. They are used to modify the oligosaccharide structure of the glycan after it has been added onto the lipid. They can also remove glycans from glycolipids to turn them back into unmodified lipids. Sphingolipidoses are a group of diseases that are associated with the accumulation of sphingolipids which have not been degraded correctly, normally due to a defect in

448-501: The correct oligosaccharide so that the right receptor can be activated on the cell which responds to the presence of the glycolipid on the surface of the cell. The glycolipid is assembled in the Golgi apparatus and embedded in the surface of a vesicle which is then transported to the cell membrane. The vesicle merges with the cell membrane so that the glycolipid can be presented on the cell's outside surface. Glycoside hydrolases catalyze

476-778: 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. 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

504-410: The enzyme phospholipase C into inositol triphosphate (IP 3 ) 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 to leukocyte signal pathways started by chemokine receptors. Phospholipids also intervene in prostaglandin signal pathways as

532-496: 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 coatings. In biological membranes,

560-404: The inner and outer surfaces of the membrane made up of the polar head groups, and the inner part of the membrane made up of the non-polar fatty acid tails. The saccharides that are attached to the polar head groups on the outside of the cell are the ligand components of glycolipids, and are likewise polar, allowing them to be soluble in the aqueous environment surrounding the cell. The lipid and

588-415: The phospholipids often occur with other molecules (e.g., proteins , glycolipids , sterols ) in a bilayer such as a cell membrane . Lipid bilayers occur when hydrophobic tails line up against one another, forming a membrane of hydrophilic heads on both sides facing the water. These specific properties allow phospholipids to play an important role in the cell membrane. Their movement can be described by

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616-411: 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. Phospholipids can act as emulsifiers , enabling oils to form a colloid with water. Phospholipids are one of the components of lecithin , which

644-409: The saccharide form a glycoconjugate through a glycosidic bond , which is a covalent bond . The anomeric carbon of the sugar binds to a free hydroxyl group on the lipid backbone. The structure of these saccharides varies depending on the structure of the molecules to which they bind. Enzymes called glycosyltransferases link the saccharide to the lipid molecule, and also play a role in assembling

672-634: The sample blood during transportation and/or storage. Phospholipids Phospholipids are a key component of all cell membranes . They can form lipid bilayers because of their amphiphilic characteristic. In eukaryotes , cell membranes also contain another class of lipid, sterol , 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 and materials science . The first phospholipid identified in 1847 as such in biological tissues

700-475: The site of inflammation. Glycolipids are also responsible for other responses, notably the recognition of host cells by viruses. Blood types are an example of how glycolipids on cell membranes mediate cell interactions with the surrounding environment. The four main human blood types (A, B, AB, O) are determined by the oligosaccharide attached to a specific glycolipid on the surface of red blood cells , which acts as an antigen . The unmodified antigen, called

728-609: The study of lipid polymorphism it is now known that the behaviour of lipids under physiological (and other) conditions is not simple. 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

756-486: Was lecithin , or phosphatidylcholine , in the egg yolk of chickens by the French chemist and pharmacist Theodore Nicolas Gobley . 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 residues. In aqueous solutions, phospholipids are driven by hydrophobic interactions , which result in

784-406: Was used to measure the intrinsic pathway. This test is called the aPTT, or activated partial thromboplastin time . It was not until much later that the subcomponents of thromboplastin and partial thromboplastin were identified. Thromboplastin is the combination of both phospholipids and tissue factor, both of which are needed in the activation of the extrinsic pathway. However, partial thromboplastin

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