A galactocerebroside is a type of cerebroside consisting of a ceramide with a galactose residue at the 1-hydroxyl moiety. The galactose is cleaved by galactosylceramidase. Galactocerebroside is a marker for oligodendrocytes in the brain. Globoid cell leukodystrophy Myelin Galactocerebrosides at the US National Library of Medicine Medical Subject Headings CHEMBL110111 image
A nerve is an enclosed, cable-like bundle of nerve fibres called axons, in the peripheral nervous system. A nerve provides a common pathway for the electrochemical nerve impulses called action potentials that are transmitted along each of the axons to peripheral organs or, in the case of sensory nerves, from the periphery back to the central nervous system; each axon within the nerve is an extension of an individual neuron, along with other supportive cells such as Schwann cells that coat the axons in myelin. Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium; the axons are bundled together into groups called fascicles, each fascicle is wrapped in a layer of connective tissue called the perineurium. The entire nerve is wrapped in a layer of connective tissue called the epineurium. In the central nervous system, the analogous structures are known as tracts; each nerve is covered on the outside by a dense sheath of the epineurium. Beneath this is a layer of flat cells, the perineurium, which forms a complete sleeve around a bundle of axons.
Perineurial septae subdivide it into several bundles of fibres. Surrounding each such fibre is the endoneurium; this forms an unbroken tube from the surface of the spinal cord to the level where the axon synapses with its muscle fibres, or ends in sensory receptors. The endoneurium consists of an inner sleeve of material called the glycocalyx and an outer, meshwork of collagen fibres. Nerves are bundled and travel along with blood vessels, since the neurons of a nerve have high energy requirements. Within the endoneurium, the individual nerve fibres are surrounded by a low-protein liquid called endoneurial fluid; this acts in a similar way to the cerebrospinal fluid in the central nervous system and constitutes a blood-nerve barrier similar to the blood-brain barrier. Molecules are thereby prevented from crossing the blood into the endoneurial fluid. During the development of nerve edema from nerve irritation, the amount of endoneurial fluid may increase at the site of irritation; this increase in fluid can be visualized using magnetic resonance neurography, thus MR neurography can identify nerve irritation and/or injury.
Nerves are categorized into three groups based on the direction that signals are conducted: Afferent nerves conduct signals from sensory neurons to the central nervous system, for example from the mechanoreceptors in skin. Efferent nerves conduct signals from the central nervous system along motor neurons to their target muscles and glands. Mixed nerves contain both afferent and efferent axons, thus conduct both incoming sensory information and outgoing muscle commands in the same bundle. Nerves can be categorized into two groups based on where they connect to the central nervous system: Spinal nerves innervate much of the body, connect through the vertebral column to the spinal cord and thus to the central nervous system, they are given letter-number designations according to the vertebra through which they connect to the spinal column. Cranial nerves innervate parts of the head, connect directly to the brain, they are assigned Roman numerals from 1 to 12, although cranial nerve zero is sometimes included.
In addition, cranial nerves have descriptive names. Specific terms are used to describe their actions. A nerve that supplies information to the brain from an area of the body, or controls an action of the body is said to "innervate" that section of the body or organ. Other terms relate to whether the nerve affects the same side or opposite side of the body, to the part of the brain that supplies it. Nerve growth ends in adolescence, but can be re-stimulated with a molecular mechanism known as "Notch signaling". If the axons of a neuron are damaged, as long as the cell body of the neuron is not damaged, the axons would regenerate and remake the synaptic connections with neurons with the help of guidepost cells; this is referred to as neuroregeneration. The nerve begins the process by destroying the nerve distal to the site of injury allowing Schwann cells, basal lamina, the neurilemma near the injury to begin producing a regeneration tube. Nerve growth factors are produced causing many nerve sprouts to bud.
When one of the growth processes finds the regeneration tube, it begins to grow towards its original destination guided the entire time by the regeneration tube. Nerve regeneration is slow and can take up to several months to complete. While this process does repair some nerves, there will still be some functional deficit as the repairs are not perfect. A nerve conveys information in the form of electrochemical impulses carried by the individual neurons that make up the nerve; these impulses are fast, with some myelinated neurons conducting at speeds up to 120 m/s. The impulses travel from one neuron to another by crossing a synapse, the message is converted from electrical to chemical and back to electrical. Nerves can be categorized into two groups based on function: An afferent nerve fiber conducts sensory information from a sensory neuron to the central nervous system, where the information is processed. Bundles of fibres or axons, in the peripheral nervous system are called nerves, bundles of afferent fibers are known as sensory nerves.
An efferent nerve fiber conducts signals from a motor neuron in the central nervous system to muscles. Bundles of these fibres are known as efferent nerves; the nervous system is the part of an animal that coordinates its actions by transmitting signals to and from different parts of its body. In vertebrates it consists of two main par
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; the name ganglioside was first applied by the German scientist Ernst Klenk in 1942 to lipids newly isolated from ganglion cells of the brain. More than 60 gangliosides are known, which differ from each other in the position and number of NANA residues, it is a component of the cell plasma membrane that modulates cell signal transduction events, appears to concentrate in lipid rafts. Gangliosides have been found to be important molecules in immunology. Natural and semisynthetic gangliosides are considered possible therapeutics for neurodegenerative disorders. Gangliosides are present and concentrated on cell surfaces, with the two hydrocarbon chains of the ceramide moiety embedded in the plasma membrane and the oligosaccharides located on the extracellular surface, where they present points of recognition for extracellular molecules or surfaces of neighboring cells.
They are found predominantly in the nervous system. The oligosaccharide groups on gangliosides extend well beyond the surfaces of the cell membranes, act as distinguishing surface markers that can serve as specific determinants in cellular recognition and cell-to-cell communication; these carbohydrate head groups act as specific receptors for certain pituitary glycoprotein hormones and certain bacterial protein toxins such as cholera toxin. The functions of gangliosides as specific determinants suggest its important role in the growth and differentiation of tissues as well as in carcinogenesis, it has been found that tumor formation can induce the synthesis of a new complement of ganglioside, low concentrations of a specific ganglioside can induce differentiation of cultured neuronal tumor cells. One NANA GM1 GM2 GM3 Two NANAs GD1a GD1b GD2 GD3 Three NANAs GT1b GT3 Four NANAs GQ1 GM2-1 = aNeu5AcbDGalpbDGalNAcbDGalNAcbDGlcpCerGM3 = aNeu5AcbDGalpbDGlcpCerGM2,GM2a = N-Acetyl-D-galactose-beta-1,4--Galactose-beta-1,4-glucose-alpha-ceramide GM2b = aNeu5AcaNeu5AcbDGalpbDGlcpCerGM1,GM1a = bDGalpbDGalNAcbDGalpbDGlcpCerasialo-GM1,GA1 = bDGalpbDGalpNAcbDGalpbDGlcpCerasialo-GM2,GA2 = bDGalpNAcbDGalpbDGlcpCerGM1b = aNeu5AcbDGalpbDGalNAcbDGalpbDGlcpCerGD3 = aNeu5AcaNeu5AcbDGalpbDGlcpCerGD2 = bDGalpNAcbDGalpbDGlcpCerGD1a = aNeu5AcbDGalpbDGalNAcbDGalpbDGlcpCerGD1alpha = aNeu5AcbDGalpbDGalNAcbDGalpbDGlcpCerGD1b = bDGalpbDGalNAcbDGalpbDGlcpCerGT1a = aNeu5AcaNeu5AcbDGalpbDGalNAcbDGalpbDGlcpCerGT1,GT1b = aNeu5AcbDGalpbDGalNAcbDGalpbDGlcpCerOAc-GT1b = aNeu5AcbDGalpbDGalNAcaXNeu5Ac9AcaNeu5Ac]bDGalpbDGlcpCerGT1c = bDGalpbDGalNAcbDGalpbDGlcpCerGT3 = aNeu5AcaNeu5AcaNeu5AcbDGalbDGlcCerGQ1b = aNeu5AcaNeu5AcbDGalpbDGalNAcbDGalpbDGlcpCerGGal = aNeu5AcbDGalpCerwhere aNeu5Ac = N-acetyl-alpha-neuraminic acid aNeu5Ac9Ac = N-acetyl-9-O-acetylneuraminic acid bDGalp = beta-D-galactopyranose bDGalpNAc = N-acetyl-beta-D-galactopyranose bDGlcp = beta-D-glucopyranose Cer = ceramide Gangliosides are continuously synthesized and degraded in cells.
They are degraded to ceramides by sequential removal of sugar units in the oligosaccharide group, catalyzed by a set of specific lysosomal enzymes. Mutations in genes coding for these enzymes leads to the accumulation of broken down gangliosides in lysosomes, which results in a group of diseases called gangliosidosis. For example, the fatal Tay–Sachs disease arises as a genetic defect which leads to no functional hexosaminidase A produced, causing GM2 to accumulate in lysosomes; the ganglion cells in the nervous system swell enormously, disturbing the normal functions of neurons. Gangliosides are involved in several diseases: Influenza, in which haemagglutinin of influenza virus exploits certain gangliosides to enter and infect the cells expressing them. Guillain–Barré syndrome, linked to the production of anti-ganglioside antibodies. Cholera Tetanus Botulism Leprosy Obesity, where inadequate ganglioside expression in mediobasal hypothalamic neurons deregulates neuronal leptin and insulin signaling.
Gangliosides at the US National Library of Medicine Medical Subject Headings Overview of gangliosides at lipidlibrary.co.uk Overview of gangliosides at cyberlipid.org
GM3 is a type of ganglioside. The letter G refers to ganglioside, M is for monosialic acid as it has one sialic acid only; the numbering is based on its relative mobility in electrophoresis among other monosialic gangliosides. Its structure can be condensed to NANA-Gal-Glc-ceramide
Sphingolipids are a class of lipids containing a backbone of sphingoid bases, 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 cell recognition. Sphingolipidoses, or disorders of sphingolipid metabolism, have particular impact on neural tissue. A sphingolipid with an R group consisting of a hydrogen atom only is a ceramide. Other common R groups include phosphocholine, yielding a sphingomyelin, various sugar monomers or dimers, yielding cerebrosides and globosides, respectively. Cerebrosides and globosides are collectively known as glycosphingolipids; the long-chain bases, sometimes known as sphingoid bases, are the first non-transient products of de novo sphingolipid synthesis in both yeast and mammals. These compounds known as phytosphingosine and dihydrosphingosine, are C18 compounds, with somewhat lower levels of C20 bases.
Ceramides and glycosphingolipids are N-acyl derivatives of these compounds. The sphingosine backbone is O-linked to a charged head group such as ethanolamine, serine, or choline; the backbone is amide-linked to an acyl group, such as a fatty acid. Simple sphingolipids, which include the sphingoid bases and ceramides, make up the early products of the sphingolipid synthetic pathways. Sphingoid bases are the fundamental building blocks of all sphingolipids; the main mammalian sphingoid bases are dihydrosphingosine and sphingosine, while dihydrosphingosine and phytosphingosine are the principle sphingoid bases in yeast. Sphingosine, dihydrosphingosine, phytosphingosine may be phosphorylated. Ceramides, as a general class, are N-acylated sphingoid bases lacking additional head groups. Dihydroceramide is produced by N-acylation of dihydrosphingosine. Dihydroceramide is found in mammalian systems. Ceramide is produced in mammalian systems by desaturation of dihydroceramide by dihydroceramide desaturase 1.
This bioactive molecule may be phosphorylated to form ceramide-1-phosphate. Phytoceramide is produced in yeast by hydroxylation of dihydroceramide at C-4. Complex sphingolipids may be formed by addition of head groups to ceramide or phytoceramide: Sphingomyelins have a phosphocholine or phosphoethanolamine molecule with an ester linkage to the 1-hydroxy group of a ceramide. Glycosphingolipids are ceramides with one or more sugar residues joined in a β-glycosidic linkage at the 1-hydroxyl position. Cerebrosides have a single galactose at the 1-hydroxy position. Sulfatides are sulfated cerebrosides. Gangliosides have at least three sugars. Inositol-containing ceramides, which are derived from phytoceramide, are produced in yeast; these include inositol phosphorylceramide, mannose inositol phosphorylceramide, mannose diinositol phosphorylceramide. De novo sphingolipid synthesis begins with formation of 3-keto-dihydrosphingosine by serine palmitoyltransferase; the preferred substrates for this reaction are serine.
However, studies have demonstrated that serine palmitoyltransferase has some activity toward other species of fatty acyl-CoA and alternative amino acids, the diversity of sphingoid bases has been reviewed. Next, 3-keto-dihydrosphingosine is reduced to form dihydrosphingosine. Dihydrosphingosine is acylated by a -ceramide synthase, such as Lass1p or Lass2p, to form dihydroceramide; this is desaturated to form ceramide. Ceramide may subsequently have several fates, it may be phosphorylated by ceramide kinase to form ceramide-1-phosphate. Alternatively, it may be glycosylated by glucosylceramide galactosylceramide synthase. Additionally, it can be converted to sphingomyelin by the addition of a phosphorylcholine headgroup by sphingomyelin synthase. Diacylglycerol is generated by this process. Ceramide may be broken down by a ceramidase to form sphingosine. Sphingosine may be phosphorylated to form sphingosine-1-phosphate; this may be dephosphorylated to reform sphingosine. Breakdown pathways allow the reversion of these metabolites to ceramide.
The complex glycosphingolipids are hydrolyzed to galactosylceramide. These lipids are hydrolyzed by beta-glucosidases and beta-galactosidases to regenerate ceramide. Sphingomyelin may be broken down by sphingomyelinase to form ceramide; the only route by which sphingolipids are converted to non-sphingolipids is through sphingosine-1-phosphate lyase. This forms ethanolamine hexadecenal. Sphingolipids are believed to protect the cell surface against harmful environmental factors by forming a mechanically stable and chemically resistant outer leaflet of the plasma membrane lipid bilayer. Certain complex glycosphingolipids were found to be involved in specific functions, such as cell recognition and signaling. Cell recognition depends on the physical properties of the sphingolipids, whereas signaling involves specific interactions of the glycan structures of glycosphingolipids with similar lipids present on neighboring cells or with proteins. Simple sphingolipid metabolites, such as ceramide and sphingosine-1-phosphate, have been shown to be important mediators in the signaling cascades involved in apoptosis, stress responses, inflammation, autophagy and differentiation.
Ceramide-based lipids self-aggregate in cell membranes and form separate phases less fluid than the bulk phospholipids. These sphingolipid-based microdomains, or "lipid rafts" were proposed to sort membrane proteins along the cellular pathways of membr
Red blood cell
Red blood cells known as RBCs, red cells, red blood corpuscles, erythroid cells or erythrocytes, are the most common type of blood cell and the vertebrate's principal means of delivering oxygen to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or gills of fish, release it into tissues while squeezing through the body's capillaries; the cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells and the blood. The cell membrane is composed of proteins and lipids, this structure provides properties essential for physiological cell function such as deformability and stability while traversing the circulatory system and the capillary network. In humans, mature red blood cells are oval biconcave disks, they lack most organelles, in order to accommodate maximum space for hemoglobin. 2.4 million new erythrocytes are produced per second in human adults. The cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages.
Each circulation takes about 60 seconds. A quarter of the cells in the human body are red blood cells. Nearly half of the blood's volume is red blood cells. Packed red blood cells are red blood cells that have been donated and stored in a blood bank for blood transfusion. All vertebrates, including all mammals and humans, have red blood cells. Red blood cells are cells present in blood; the only known vertebrates without red blood cells are the crocodile icefish. While they no longer use hemoglobin, remnants of hemoglobin genes can be found in their genome. Vertebrate red blood cells consist of hemoglobin, a complex metalloprotein containing heme groups whose iron atoms temporarily bind to oxygen molecules in the lungs or gills and release them throughout the body. Oxygen can diffuse through the red blood cell's cell membrane. Hemoglobin in the red blood cells carries some of the waste product carbon dioxide back from the tissues. Myoglobin, a compound related to hemoglobin, acts to store oxygen in muscle cells.
The color of red blood cells is due to the heme group of hemoglobin. The blood plasma alone is straw-colored, but the red blood cells change color depending on the state of the hemoglobin: when combined with oxygen the resulting oxyhemoglobin is scarlet, when oxygen has been released the resulting deoxyhemoglobin is of a dark red burgundy color. However, blood can appear bluish when seen through skin. Pulse oximetry takes advantage of the hemoglobin color change to directly measure the arterial blood oxygen saturation using colorimetric techniques. Hemoglobin has a high affinity for carbon monoxide, forming carboxyhemoglobin, a bright red in color. Flushed, confused patients with a saturation reading of 100% on pulse oximetry are sometimes found to be suffering from carbon monoxide poisoning. Having oxygen-carrying proteins inside specialized cells was an important step in the evolution of vertebrates as it allows for less viscous blood, higher concentrations of oxygen, better diffusion of oxygen from the blood to the tissues.
The size of red blood cells varies among vertebrate species. The red blood cells of mammals are shaped as biconcave disks: flattened and depressed in the center, with a dumbbell-shaped cross section, a torus-shaped rim on the edge of the disk; this shape allows for a high surface-area-to-volume ratio to facilitate diffusion of gases. However, there are some exceptions concerning shape in the artiodactyl order, which displays a wide variety of bizarre red blood cell morphologies: small and ovaloid cells in llamas and camels, tiny spherical cells in mouse deer, cells which assume fusiform, lanceolate and irregularly polygonal and other angular forms in red deer and wapiti. Members of this order have evolved a mode of red blood cell development different from the mammalian norm. Overall, mammalian red blood cells are remarkably flexible and deformable so as to squeeze through tiny capillaries, as well as to maximize their apposing surface by assuming a cigar shape, where they efficiently release their oxygen load.
Red blood cells in mammals are unique amongst vertebrates. Red blood cells of mammals cells have nuclei during early phases of erythropoiesis, but extrude them during development as they mature; the red blood cells without nuclei, called reticulocytes, subsequently lose all other cellular organelles such as their mitochondria, Golgi apparatus and endoplasmic reticulum. The spleen acts as a reservoir of red blood cells. In some other mammals such as dogs and horses, the spl
Polysaccharides are polymeric carbohydrate molecules composed of long chains of monosaccharide units bound together by glycosidic linkages, on hydrolysis give the constituent monosaccharides or oligosaccharides. They range in structure from linear to branched. Examples include storage polysaccharides such as starch and glycogen, structural polysaccharides such as cellulose and chitin. Polysaccharides are quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure, these macromolecules can have distinct properties from their monosaccharide building blocks, they may be amorphous or insoluble in water. When all the monosaccharides in a polysaccharide are the same type, the polysaccharide is called a homopolysaccharide or homoglycan, but when more than one type of monosaccharide is present they are called heteropolysaccharides or heteroglycans. Natural saccharides are of simple carbohydrates called monosaccharides with general formula n where n is three or more.
Examples of monosaccharides are glucose and glyceraldehyde. Polysaccharides, have a general formula of Cxy where x is a large number between 200 and 2500; when the repeating units in the polymer backbone are six-carbon monosaccharides, as is the case, the general formula simplifies to n, where 40≤n≤3000. As a rule of thumb, polysaccharides contain more than ten monosaccharide units, whereas oligosaccharides contain three to ten monosaccharide units. Polysaccharides are an important class of biological polymers, their function in living organisms is either structure- or storage-related. Starch is used as a storage polysaccharide in plants, being found in the form of both amylose and the branched amylopectin. In animals, the structurally similar glucose polymer is the more densely branched glycogen, sometimes called "animal starch". Glycogen's properties allow it to be metabolized more which suits the active lives of moving animals. Cellulose and chitin are examples of structural polysaccharides.
Cellulose is used in the cell walls of plants and other organisms, is said to be the most abundant organic molecule on Earth. It has many uses such as a significant role in the paper and textile industries, is used as a feedstock for the production of rayon, cellulose acetate and nitrocellulose. Chitin has nitrogen-containing side branches, increasing its strength, it is found in the cell walls of some fungi. It has multiple uses, including surgical threads. Polysaccharides include callose or laminarin, xylan, mannan and galactomannan. Nutrition polysaccharides are common sources of energy. Many organisms can break down starches into glucose; these carbohydrate types can be metabolized by some protists. Ruminants and termites, for example, use microorganisms to process cellulose. Though these complex polysaccharides are not digestible, they provide important dietary elements for humans. Called dietary fiber, these carbohydrates enhance digestion among other benefits; the main action of dietary fiber is to change the nature of the contents of the gastrointestinal tract, to change how other nutrients and chemicals are absorbed.
Soluble fiber binds to bile acids in the small intestine, making them less to enter the body. Soluble fiber attenuates the absorption of sugar, reduces sugar response after eating, normalizes blood lipid levels and, once fermented in the colon, produces short-chain fatty acids as byproducts with wide-ranging physiological activities. Although insoluble fiber is associated with reduced diabetes risk, the mechanism by which this occurs is unknown. Not yet formally proposed as an essential macronutrient, dietary fiber is regarded as important for the diet, with regulatory authorities in many developed countries recommending increases in fiber intake. Starch is a glucose polymer, it is made up of a mixture of amylopectin. Amylose consists of a linear chain of several hundred glucose molecules and Amylopectin is a branched molecule made of several thousand glucose units. Starches are insoluble in water, they can be digested by breaking the alpha-linkages. Both humans and other animals have amylases, so they can digest starches.
Potato, rice and maize are major sources of starch in the human diet. The formations of starches are the ways. Glycogen serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue. Glycogen is made by the liver and the muscles, but can be made by glycogenesis within the brain and stomach. Glycogen is analogous to starch, a glucose polymer in plants, is sometimes referred to as animal starch, having a similar structure to amylopectin but more extensively branched and compact than starch. Glycogen is a polymer of α glycosidic bonds linked, with α-linked branches. Glycogen is found in the form of granules in the cytosol/cytoplasm in many cell types, plays an important role in the glucose cycle. Glycogen forms an energy reserve that can be mobilized to meet a sudden need for glucose, but one, less compact and more available a