Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins, monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing energy, signaling, and acting as structural components of cell membranes. Lipids have applications in the cosmetic and food industries, and in nanotechnology.
An oligosaccharide is a saccharide polymer containing a small number of monosaccharides. Oligosaccharides can have many functions including cell recognition and cell adhesion.
In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. These can be activated by enzyme hydrolysis, which causes the sugar part to be broken off, making the chemical available for use. Many such plant glycosides are used as medications. Several species of Heliconius butterfly are capable of incorporating these plant compounds as a form of chemical defense against predators. In animals and humans, poisons are often bound to sugar molecules as part of their elimination from the body.
Sialic acids are a class of alpha-keto acid sugars with a nine-carbon backbone. The term "sialic acid" was first introduced by Swedish biochemist Gunnar Blix in 1952. The most common member of this group is N-acetylneuraminic acid found in animals and some prokaryotes.
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 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.
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 sphinx because of their enigmatic nature. These compounds play important roles in signal transduction and cell recognition. Sphingolipidoses, or disorders of sphingolipid metabolism, have particular impact on neural tissue. A sphingolipid with a terminal hydroxyl group is a ceramide. Other common groups bonded to the terminal oxygen atom include phosphocholine, yielding a sphingomyelin, and various sugar monomers or dimers, yielding cerebrosides and globosides, respectively. Cerebrosides and globosides are collectively known as glycosphingolipids.
Sphingomyelin is a type of sphingolipid found in animal cell membranes, especially in the membranous myelin sheath that surrounds some nerve cell axons. It usually consists of phosphocholine and ceramide, or a phosphoethanolamine head group; therefore, sphingomyelins can also be classified as sphingophospholipids. In humans, SPH represents ~85% of all sphingolipids, and typically make up 10–20 mol % of plasma membrane lipids.
A ganglioside is a molecule composed of a glycosphingolipid with one or more sialic acids linked on the sugar chain. NeuNAc, an acetylated derivative of the carbohydrate sialic acid, makes the head groups of gangliosides anionic at pH 7, which distinguishes them from globosides.
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. Two major classes are known: those for bacteria and eukaryotes and a separate family for archaea.
Ceramides are a family of waxy lipid molecules. A ceramide is composed of sphingosine and a fatty acid joined by an amide bond. Ceramides are found in high concentrations within the cell membrane of eukaryotic cells, since they are component lipids that make up sphingomyelin, one of the major lipids in the lipid bilayer. Contrary to previous assumptions that ceramides and other sphingolipids found in cell membrane were purely supporting structural elements, ceramide can participate in a variety of cellular signaling: examples include regulating differentiation, proliferation, and programmed cell death (PCD) of cells.
Cerebrosides (monoglycosylceramides) are a group of glycosphingolipids which are important components of animal muscle and nerve cell membranes.
Lipid signaling, broadly defined, refers to any biological cell signaling event involving a lipid messenger that binds a protein target, such as a receptor, kinase or phosphatase, which in turn mediate the effects of these lipids on specific cellular responses. Lipid signaling is thought to be qualitatively different from other classical signaling paradigms because lipids can freely diffuse through membranes. One consequence of this is that lipid messengers cannot be stored in vesicles prior to release and so are often biosynthesized "on demand" at their intended site of action. As such, many lipid signaling molecules cannot circulate freely in solution but, rather, exist bound to special carrier proteins in serum.
Sulfatide, also known as 3-O-sulfogalactosylceramide, SM4, or sulfated galactocerebroside, is a class of sulfolipids, specifically a class of sulfoglycolipids, which are glycolipids that contain a sulfate group. Sulfatide is synthesized primarily starting in the endoplasmic reticulum and ending in the Golgi apparatus where ceramide is converted to galactocerebroside and later sulfated to make sulfatide. Of all of the galactolipids that are found in the myelin sheath, one fifth of them are sulfatide. Sulfatide is primarily found on the extracellular leaflet of the myelin plasma membrane produced by the oligodendrocytes in the central nervous system and in the Schwann cells in the peripheral nervous system. However, sulfatide is also present on the extracellular leaflet of the plasma membrane of many cells in eukaryotic organisms.
Sialyltransferases are enzymes that transfer sialic acid to nascent oligosaccharide. Each sialyltransferase is specific for a particular sugar substrate. Sialyltransferases add sialic acid to the terminal portions of the sialylated glycolipids (gangliosides) or to the N- or O-linked sugar chains of glycoproteins.
Membrane lipids are a group of compounds which form the lipid bilayer of the cell membrane. The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol. Lipids are amphiphilic: they have one end that is soluble in water ('polar') and an ending that is soluble in fat ('nonpolar'). By forming a double layer with the polar ends pointing outwards and the nonpolar ends pointing inwards membrane lipids can form a 'lipid bilayer' which keeps the watery interior of the cell separate from the watery exterior. The arrangements of lipids and various proteins, acting as receptors and channel pores in the membrane, control the entry and exit of other molecules and ions as part of the cell's metabolism. In order to perform physiological functions, membrane proteins are facilitated to rotate and diffuse laterally in two dimensional expanse of lipid bilayer by the presence of a shell of lipids closely attached to protein surface, called annular lipid shell.
Polysialic acid is an unusual posttranslational modification that occurs on neural cell adhesion molecules (NCAM). Polysialic acid is considerably anionic. This strong negative charge gives this modification the ability to change the protein's surface charge and binding ability. In the synapse, polysialation of NCAM prevents its ability to bind to NCAMs on the adjacent membrane.
GM3 (monosialodihexosylganglioside) is a type of ganglioside. The letter G refers to ganglioside, and M is for monosialic acid as it has only one sialic acid group. The numbering is based on its relative mobility in electrophoresis among other monosialic gangliosides. Its structure can be condensed to NANA-Gal-Glc-ceramide. GM3 is the most common membrane-bound glycosphingolipid in tissues, composed of three monosaccharide groups attached to a ceramide backbone. GM3 serves as a precursor for other, more complex gangliosides. Like other gangliosides, GM3 is synthesized in the Golgi apparatus. It is then transported to the plasma membrane, where it functions in cellular signaling. GM3 also functions as an inhibitor; it inhibits cell growth, the function of growth factor receptors, and generation of cytokines by T cells.
Milk fat globule membrane (MFGM) is a complex and unique structure composed primarily of lipids and proteins that surrounds milk fat globule secreted from the milk producing cells of humans and other mammals. It is a source of multiple bioactive compounds, including phospholipids, glycolipids, glycoproteins, and carbohydrates that have important functional roles within the brain and gut.
The 1-deoxysphingolipids (1-deoxySLs) are an atypical and recently discovered class of sphingolipids (SLs). They are formed during the nove synthesis pathway and their essential C1-OH deficit causes the malfunctions of the following transformations to achieve complex sphingolipids. In general, sphingolipids are formed during a reaction that is catalyzed by the SPT enzyme (serine-palmitoyltransferase) where the condensation of serine and palmitoyl-CoA takes place. The origin of this rare sphingolipid, though, is due to a defect of the SPT which can also use alanine or glycine. This change is what forms the 1-deoxySL.
Ernst Klenk was a German biochemist, known as a pioneer in research on biolipids, their metabolism, and diseases caused by biolipid disorders.
