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Eat-me Signals
Eat-me signals are molecules exposed on the surface of a cell to induce phagocytes to Phagocytosis, phagocytose (eat) that cell. Currently known eat-me signals include: phosphatidylserine, oxidized phospholipids, sugar residues (such as galactose), DNA, deoxyribonucleic acid (DNA), calreticulin, annexin A1, histones and Pentraxins, pentraxin-3 (PTX3). The most well characterised eat-me signal is the phospholipid phosphatidylserine. Healthy cells do not expose phosphatidylserine on their surface, whereas dead, dying, infected, injured and some activated cells expose phosphatidylserine on their surface in order to induce phagocytes to phagocytose them. Most glycoproteins and glycolipids on the surface of our cells have short sugar chains that terminate in sialic acid residues, which inhibit phagocytosis, but removal of these residues reveals galactose residues (and subsequently N-Acetylglucosamine, N-acetylglucosamine and mannose residues) that can bind opsonins or directly activate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glycoprotein
Glycoproteins are proteins which contain oligosaccharide chains covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. Secreted extracellular proteins are often glycosylated. In proteins that have segments extending extracellularly, the extracellular segments are also often glycosylated. Glycoproteins are also often important integral membrane proteins, where they play a role in cell–cell interactions. It is important to distinguish endoplasmic reticulum-based glycosylation of the secretory system from reversible cytosolic-nuclear glycosylation. Glycoproteins of the cytosol and nucleus can be modified through the reversible addition of a single GlcNAc residue that is considered reciprocal to phosphorylation and the functions of these are likely to be an additional regulatory mechanism that controls phosphorylation-based signalling. In contrast, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Find-me Signals
Find-me signals Cells destined for apoptosis release molecules referred to as find me signals. These signal molecules are used to attract phagocytes which engulf and eliminate damaged cells. Find-me signals are typically released by the apoptotic cells while the cell membrane remains intact. This ensures that the phagocytic cells are able to remove the dying cells before their membranes are compromised. A leaky membrane leads to secondary necrosis which may cause additional inflammation, therefore, it is best to remove dying cells before this occurs. One cell is capable of releasing multiple find-me signals. Should a cell lack the ability to release its find-me signal, other cells may release additional find-me signals to overcome the discrepancy. Additional roles of Find-me signals Inflammation can be suppressed by find-me signals during cell clearance. A phagocyte may also be able to engulf more material or enhance its ability to engulf materials when stimulated by find-me signal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Opsonin
Opsonins are extracellular proteins that, when bound to substances or cells, induce phagocytes to phagocytose the substances or cells with the opsonins bound. Thus, opsonins act as tags to label things in the body that should be phagocytosed (i.e. eaten) by phagocytes (cells that specialise in phagocytosis, i.e. cellular eating). Different types of things ("targets") can be tagged by opsonins for phagocytosis, including: pathogens (such as bacteria), cancer cells, aged cells, dead or dying cells (such as apoptotic cells), excess synapses, or protein aggregates (such as amyloid plaques). Opsonins help clear pathogens, as well as dead, dying and diseased cells. Opsonins were discovered and named "opsonins" in 1904 by Wright and Douglas, who found that incubating bacteria with blood plasma enabled phagocytes to phagocytose (and thereby destroy) the bacteria. They concluded that: “We have here conclusive proof that the blood fluids modify the bacteria in a manner which renders them ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mannose
Mannose is a sugar monomer of the aldohexose series of carbohydrates. It is a C-2 epimer of glucose. Mannose is important in human metabolism, especially in the glycosylation of certain proteins. Several congenital disorders of glycosylation are associated with mutations in enzymes involved in mannose metabolism. Mannose is not an essential nutrient; it can be produced in the human body from glucose, or converted into glucose. Mannose provides 2–5 kcal/g. It is partially excreted in the urine. Etymology The root of both "mannose" and "mannitol" is manna, which the Bible describes as the food supplied to the Israelites during their journey in the region of Sinai. Several trees and shrubs can produce a substance called manna, such as the "manna tree" ('' Fraxinus ornus'') from whose secretions mannitol was originally isolated. Structure Mannose commonly exists as two different-sized rings, the pyranose (six-membered) form and the furanose (five-membered) form. Eac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
N-Acetylglucosamine
''N''-Acetylglucosamine (GlcNAc) is an amide derivative of the monosaccharide glucose. It is a secondary amide between glucosamine and acetic acid. It is significant in several biological systems. It is part of a biopolymer in the bacterial cell wall, which is built from alternating units of GlcNAc and ''N''-acetylmuramic acid (MurNAc), cross-linked with oligopeptides at the lactic acid residue of MurNAc. This layered structure is called peptidoglycan (formerly called murein). GlcNAc is the monomeric unit of the polymer chitin, which forms the exoskeletons of arthropods like insects and crustaceans. It is the main component of the radulas of mollusks, the beaks of cephalopods, and a major component of the cell walls of most fungi. Polymerized with glucuronic acid, it forms hyaluronan. GlcNAc has been reported to be an inhibitor of elastase release from human polymorphonuclear leukocytes (range 8–17% inhibition), however this is much weaker than the inhibition seen wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phagocytosis
Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis is called a phagocyte. In a multicellular organism's immune system, phagocytosis is a major mechanism used to remove pathogens and cell debris. The ingested material is then digested in the phagosome. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytized. Some protozoa use phagocytosis as means to obtain nutrients. History Phagocytosis was first noted by Canadian physician William Osler (1876), and later studied and named by Élie Metchnikoff (1880, 1883). In immune system Phagocytosis is one main mechanisms of the innate immune defense. It is one of the first processes responding to infection, and is also one of the initiating branches of an adaptive immune response. Although mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sialic Acid
Sialic acids are a class of alpha-keto acid sugars with a nine-carbon backbone. The term "sialic acid" (from the Greek for saliva, - ''síalon'') was first introduced by Swedish biochemist Gunnar Blix in 1952. The most common member of this group is ''N''-acetylneuraminic acid (Neu5Ac or NANA) found in animals and some prokaryotes. Sialic acids are found widely distributed in animal tissues and related forms are found to a lesser extent in other organisms like in some micro-algae, bacteria and archaea. Sialic acids are commonly part of glycoproteins, glycolipids or gangliosides, where they decorate the end of sugar chains at the surface of cells or soluble proteins. However, sialic acids have been also observed in ''Drosophila'' embryos and other insects. Generally, plants seem not to contain or display sialic acids. In humans the brain has the highest sialic acid content, where these acids play an important role in neural transmission and ganglioside structure in synaptogene ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glycolipid
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. Structure The essential feature of 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 the inner and outer surfaces of the membrane made up of the pol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pentraxins
Pentraxins (PTX), also known as pentaxins, are an evolutionary conserved family of proteins characterised by containing a pentraxin protein domain. Proteins of the pentraxin family are involved in acute immunological responses. They are a class of pattern recognition receptors (PRRs). They are a superfamily of multifunctional conserved proteins, some of which are components of the humoral arm of innate immunity and behave as functional ancestors of antibodies (Abs). They are known as classical acute phase proteins (APP), known for over a century. Structure Pentraxins are characterised by calcium dependent ligand binding and a distinctive flattened β-jellyroll structure similar to that of the legume lectins. The name "pentraxin" is derived from the Greek word for five (penta) and axle (axis) relating to the radial symmetry of five monomers forming a ring approximately 95Å across and 35Å deep observed in the first members of this family to be identified. The "short" pentra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phagocyte
Phagocytes are cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. Their name comes from the Greek ', "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell", from the Greek ''kutos'', "hollow vessel". They are essential for fighting infections and for subsequent immunity. Phagocytes are important throughout the animal kingdom and are highly developed within vertebrates. One litre of human blood contains about six billion phagocytes. They were discovered in 1882 by Ilya Ilyich Mechnikov while he was studying starfish larvae.Ilya Mechnikov retrieved on November 28, 2008. Fro ''Physiology or Medicine 1901–1921'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Histone
In biology, histones are highly basic proteins abundant in lysine and arginine residues that are found in eukaryotic cell nuclei. They act as spools around which DNA winds to create structural units called nucleosomes. Nucleosomes in turn are wrapped into 30-nanometer fibers that form tightly packed chromatin. Histones prevent DNA from becoming tangled and protect it from DNA damage. In addition, histones play important roles in gene regulation and DNA replication. Without histones, unwound DNA in chromosomes would be very long. For example, each human cell has about 1.8 meters of DNA if completely stretched out; however, when wound about histones, this length is reduced to about 90 micrometers (0.09 mm) of 30 nm diameter chromatin fibers. There are five families of histones which are designated H1/H5 (linker histones), H2, H3, and H4 (core histones). The nucleosome core is formed of two H2A-H2B dimers and a H3-H4 tetramer. The tight wrapping of DNA around histones ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
