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History Of Cell Membrane Theory
Cell theory has its origins in seventeenth century histology, microscopy observations, but it was nearly two hundred years before a complete cell membrane theory was developed to explain what separates cells from the outside world. By the 19th century it was accepted that some form of semi-permeable barrier must exist around a cell. Studies of the action of anesthetic molecules led to the theory that this barrier might be made of some sort of fat (lipid), but the structure was still unknown. A series of pioneering experiments in 1925 indicated that this barrier membrane consisted of two molecular layers of lipids—a lipid bilayer. New tools over the next few decades confirmed this theory, but controversy remained regarding the role of proteins in the cell membrane. Eventually the Cell membrane#Structure and the Fluid mosaic model, fluid mosaic model was composed in which proteins “float” in a fluid lipid bilayer "sea". Although simplistic and incomplete, this model is still widel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Theory
In biology, cell theory is a scientific theory first formulated in the mid-nineteenth century, that living organisms are made up of Cell (biology), cells, that they are the basic structural/organizational unit of all organisms, and that all cells come from pre-existing cells. Cells are the basic unit of structure in all organisms and also the basic unit of reproduction. The three tenets of the cell theory are: # All living organisms are composed of one or more cells. # The cell is the basic unit of structure and organization in organisms. # Cells arise from pre-existing cells. The theory was once universally accepted, but now some biologists consider non-cellular life, non-cellular entities such as viruses living organisms, and thus disagree with the first tenet. As of 2021: "expert opinion remains divided roughly a third each between yes, no and don’t know". As there is no universally accepted definition of Life#Definition, life, discussion will continue. History With contin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Georg Hermann Quincke
Georg Hermann Quincke FRSFor HFRSE (; November 19, 1834 – January 13, 1924) was a German physicist. Biography Born in Frankfurt-on-Oder, Quincke was the son of prominent physician ''Geheimer Medicinal-Rath'' Hermann Quincke and the older brother of physician Heinrich Quincke. Quincke received his Ph. D. in 1858 at Berlin, having previously studied also at Königsberg and at Heidelberg. He became privatdocent at Berlin in 1859, professor at Berlin in 1865, professor at Würzburg in 1872, and in 1875 was called to be professor of physics at Heidelberg, where he remained until his retirement in 1907. His doctor's dissertation was on the subject of the capillary constant of mercury, and his investigations of all capillary phenomena are classical. In September 1860, Quincke was one of the participants in the Karlsruhe Congress, the first international conference of chemistry worldwide. He and Adolf von Baeyer represented the University of Berlin in Congress. Quincke also di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or exemplified by the odors of gasoline and lighter fluid. They occur in a diverse range of molecular structures and phases: they can be gases (such as methane and propane), liquids (such as hexane and benzene), low melting solids (such as paraffin wax and naphthalene) or polymers (such as polyethylene and polystyrene). In the fossil fuel industries, ''hydrocarbon'' refers to the naturally occurring petroleum, natural gas and coal, and to their hydrocarbon derivatives and purified forms. Combustion of hydrocarbons is the main source of the world's energy. Petroleum is the dominant raw-material source for organic commodity chemicals such as solvents and polymers. Most anthropogenic (human-generated) emissions of greenhouse gases are carbon di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemical Polarity
In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole moment, with a negatively charged end and a positively charged end. Polar molecules must contain one or more polar bonds due to a difference in electronegativity between the bonded atoms. Molecules containing polar bonds have no molecular polarity if the bond dipoles cancel each other out by symmetry. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Polarity underlies a number of physical properties including surface tension, solubility, and melting and boiling points. Polarity of bonds Not all atoms attract electrons with the same force. The amount of "pull" an atom exerts on its electrons is called its electronegativity. Atoms with high electronegativitiessuch as fluorine, oxygen, and nitrogenexert a greater pull on electrons than atoms with lower electronegativities such as alkali metals and alkaline ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Erythrocyte
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hollow vessel", with ''-cyte'' translated as "cell" in modern usage), are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O2) to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or in fish the gills, and release it into tissues while squeezing through the body's capillaries. The cytoplasm of a red blood cell 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. Each human red blood cell contains approximately 270 million hemoglobin molecules. The cell membrane is composed of proteins and lipids, and this structure provides properties essential for physiologi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Capacitance
Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are two closely related notions of capacitance: ''self capacitance'' and ''mutual capacitance''. An object that can be electrically charged exhibits self capacitance, for which the electric potential is measured between the object and ground. Mutual capacitance is measured between two components, and is particularly important in the operations of the capacitor, a device designed for this purpose as an elementary Linear circuit, linear electronic component. Capacitance is a function only of the geometry of the design of the capacitor, e.g., the opposing surface area of the plates and the distance between them, and the permittivity of the dielectric material between the plates. For many dielectric materials, the permittivity and thus the capaci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Annular Gap Junction Vesicle
Annulus (or anulus) or annular indicates a ring- or donut-shaped area or structure. It may refer to: Human anatomy * ''Anulus fibrosus disci intervertebralis'', spinal structure * Annulus of Zinn, a.k.a. annular tendon or ''anulus tendineus communis'', around the optic nerve * Annular ligament (other) * ''Digitus anularis'', a.k.a. ring finger * ''Anulus ciliaris'', a.k.a. ciliary body * ''Anulus femoralis'', a.k.a. femoral ring * ''Anulus inguinalis superficialis'', a.k.a. superficial inguinal ring * ''Anulus inguinalis profundus'', a.k.a. deep inguinal ring * ''Anuli fibrosi cordis'', a.k.a. fibrous rings of heart * ''Anulus umbilicalis '', a.k.a. umbilical ring Other * Annulus (construction), outer gear ring in an epicyclic gearing * Annulus (botany), structure on fern and moss sporangia * Annular lake, a ring-shaped lake caused by meteor impact * Annulus (mathematics), the shape between two concentric circles * Annulus (mycology), structure on mushroom * Annulus ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Integral Membrane Proteins
An integral, or intrinsic, membrane protein (IMP) is a type of membrane protein that is permanently attached to the biological membrane. All ''transmembrane proteins'' are IMPs, but not all IMPs are transmembrane proteins. IMPs comprise a significant fraction of the proteins encoded in an organism's genome. Proteins that cross the membrane are surrounded by annular lipids, which are defined as lipids that are in direct contact with a membrane protein. Such proteins can only be separated from the membranes by using detergents, nonpolar solvents, or sometimes denaturing agents. Structure Three-dimensional structures of ~160 different integral membrane proteins have been determined at atomic resolution by X-ray crystallography or nuclear magnetic resonance spectroscopy. They are challenging subjects for study owing to the difficulties associated with extraction and crystallization. In addition, structures of many water-soluble protein domains of IMPs are available in the Prote ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cholesterol
Cholesterol is any of a class of certain organic molecules called lipids. It is a sterol (or modified steroid), a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell membranes. When chemically isolated, it is a yellowish crystalline solid. Cholesterol also serves as a precursor for the biosynthesis of steroid hormones, bile acid and vitamin D. Cholesterol is the principal sterol synthesized by all animals. In vertebrates, hepatic cells typically produce the greatest amounts. It is absent among prokaryotes (bacteria and archaea), although there are some exceptions, such as '' Mycoplasma'', which require cholesterol for growth. François Poulletier de la Salle first identified cholesterol in solid form in gallstones in 1769. However, it was not until 1815 that chemist Michel Eugène Chevreul named the compound "cholesterine". Etymology The word "cholesterol" comes from the Ancient Greek ''chole-'' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phosphatidylcholine
Phosphatidylcholines (PC) are a class of phospholipids that incorporate choline as a headgroup. They are a major component of biological membranes and can be easily obtained from a variety of readily available sources, such as egg yolk or soybeans, from which they are mechanically or chemically extracted using hexane. They are also a member of the lecithin group of yellow-brownish fatty substances occurring in animal and plant tissues. Dipalmitoyl phosphatidylcholine (a.k.a. lecithin) is a major component of pulmonary surfactant and is often used in the L/S ratio to calculate fetal lung maturity. While phosphatidylcholines are found in all plant and animal cells, they are absent in the membranes of most bacteria, including ''Escherichia coli''. Purified phosphatidylcholine is produced commercially. The name ''lecithin'' was derived from Greek λέκιθος, ''lekithos'' 'egg yolk' by Theodore Nicolas Gobley, a French chemist and pharmacist of the mid-19th century, who appli ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Outdated Theories Of Anaesthetic Action
A general anaesthetic (or anesthetic) is a drug that brings about a reversible loss of consciousness. These drugs are generally administered by an anaesthetist/anesthesiologist in order to induce or maintain general anaesthesia to facilitate surgery. General anaesthetics have been widely used in surgery since 1842 when Crawford Long for the first time administered diethyl ether to a patient and performed a painless operation. It has long been believed that general anaesthetics exert their effects (analgesia, unconsciousness, immobility) through a membrane mediated mechanism or by directly modulating the activity of membrane proteins in the neuronal membrane. In general, different anaesthetics exhibit different mechanisms of action such that there are numerous molecular targets at all levels of integration within the central nervous system. However, for certain intravenous anaesthetics, such as propofol and etomidate, the main molecular target has been identified to be GABAA rece ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anesthetics
An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia — in other words, to result in a temporary loss of sensation or awareness. They may be divided into two broad classes: general anesthetics, which result in a reversible loss of consciousness, and local anesthetics, which cause a reversible loss of sensation for a limited region of the body without necessarily affecting consciousness. A wide variety of drugs are used in modern anesthetic practice. Many are rarely used outside anesthesiology, but others are used commonly in various fields of healthcare. Combinations of anesthetics are sometimes used for their synergistic and additive therapeutic effects. Adverse effects, however, may also be increased. Anesthetics are distinct from analgesics, which block only sensation of painful stimuli. Local anesthetics Local anesthetic agents prevent the transmission of nerve impulses without causi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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