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Membrane Lipids
Membrane lipids are a group of compounds (structurally similar to fats and oils) which form the double-layered surface of all cells (lipid bilayer). 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Membrane Lipids
Membrane lipids are a group of compounds (structurally similar to fats and oils) which form the double-layered surface of all cells (lipid bilayer). 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lipid Bilayer
The lipid bilayer (or phospholipid bilayer) is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many viruses are made of a lipid bilayer, as are the nuclear membrane surrounding the cell nucleus, and membranes of the membrane-bound organelles in the cell. The lipid bilayer is the barrier that keeps ions, proteins and other molecules where they are needed and prevents them from diffusing into areas where they should not be. Lipid bilayers are ideally suited to this role, even though they are only a few nanometers in width, because they are impermeable to most water-soluble (hydrophilic) molecules. Bilayers are particularly impermeable to ions, which allows cells to regulate salt concentrations and pH by transporting ions across their membranes using proteins called ion pumps. Biological bilayers are usually composed of amphiphilic phosphol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Membrane Fluidity
In biology, membrane fluidity refers to the viscosity of the lipid bilayer of a cell membrane or a synthetic lipid membrane. Lipid packing can influence the fluidity of the membrane. Viscosity of the membrane can affect the rotation and diffusion of proteins and other bio-molecules within the membrane, there-by affecting the functions of these things. Membrane fluidity is affected by fatty acids. More specifically, whether the fatty acids are saturated or unsaturated has an effect on membrane fluidity. Saturated fatty acids have no double bonds in the hydrocarbon chain, and the maximum amount of hydrogen. The absence of double bonds decreases fluidity, making the membrane very strong and stacked tightly. Unsaturated fatty acids have at least one double bond, creating a "kink" in the chain. The double bond increases fluidity. Membrane fluidity is also affected by cholesterol. Cholesterol can make the cell membrane fluid as well as rigid. Factors determining membrane fluidity Membra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Saturated And Unsaturated Compounds
In chemistry, a saturated compound is a chemical compound (or ion) that resists the addition reactions, such as hydrogenation, oxidative addition, and binding of a Lewis acids and bases, Lewis base. The term is used in many contexts and for many classes of chemical compounds. Overall, saturated compounds are less reactive than unsaturated compounds. Saturation is derived from the Latin word ''saturare'', meaning 'to fill'. Organic chemistry Unsaturated compounds generally carry out typical addition reactions that are not possible with saturated compounds such as alkanes. A saturated organic compound has only single bonds between carbon atoms. An important class of saturated compounds are the alkanes. Many saturated compounds have functional groups, e.g., alcohols. Unsaturated organic compounds The concept of saturation can be described using various naming systems, formulas, and Analytical chemistry, analytical tests. For instance, IUPAC nomenclature of organic chemistry, IU ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cis–trans Isomerism
''Cis''–''trans'' isomerism, also known as geometric isomerism or configurational isomerism, is a term used in chemistry that concerns the spatial arrangement of atoms within molecules. The prefixes "''cis''" and "''trans''" are from Latin: "this side of" and "the other side of", respectively. In the context of chemistry, ''cis'' indicates that the functional groups (substituents) are on the same side of some plane, while ''trans'' conveys that they are on opposing (transverse) sides. ''Cis''–''trans'' isomers are stereoisomers, that is, pairs of molecules which have the same formula but whose functional groups are in different orientations in three-dimensional space. ''Cis-trans'' notation does not always correspond to E–Z notation, ''E''–''Z'' isomerism, which is an ''Absolute configuration, absolute'' stereochemical description. In general, ''cis''–''trans'' stereoisomers contain double bonds that do not rotate, or they may contain ring structures, where the rotation ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Double Bond
In chemistry, a double bond is a covalent bond between two atoms involving four bonding electrons as opposed to two in a single bond. Double bonds occur most commonly between two carbon atoms, for example in alkenes. Many double bonds exist between two different elements: for example, in a carbonyl group between a carbon atom and an oxygen atom. Other common double bonds are found in azo compounds (N=N), imines (C=N), and sulfoxides (S=O). In a skeletal formula, a double bond is drawn as two parallel lines (=) between the two connected atoms; typographically, the equals sign is used for this. Double bonds were first introduced in chemical notation by Russian chemist Alexander Butlerov. Double bonds involving carbon are stronger and shorter than single bonds. The bond order is two. Double bonds are also electron-rich, which makes them potentially more reactive in the presence of a strong electron acceptor (as in addition reactions of the halogens). File:Ethene structural.svg ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopes Of Carbon
Carbon (6C) has 15 known isotopes, from to , of which and are stable nuclide, stable. The longest-lived radionuclide, radioisotope is , with a half-life of years. This is also the only carbon radioisotope found in nature—trace quantities are formed cosmogenic nuclide, cosmogenically by the reaction + → + . The most stable artificial radioisotope is , which has a half-life of . All other radioisotopes have half-lives under 20 seconds, most less than 200 milliseconds. The least stable isotope is , with a half-life of . List of isotopes , - , , style="text-align:right" , 6 , style="text-align:right" , 2 , , [] , proton emission, 2p , Subsequently decays by double proton emission to for a net reaction of → + 4 , 0+ , , , - , rowspan=3, , rowspan=3 style="text-align:right" , 6 , rowspan=3 style="text-align:right" , 3 , rowspan=3, , rowspan=3, , β+ () , , rowspan=3, 3/2− , rowspan=3, , rowspan=3, , - , β+α () , Immediately decays ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, or affinity of an ...—its atom making four electrons available to form covalent bond, covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three Isotopes of carbon, isotopes occur naturally, Carbon-12, C and Carbon-13, C being stable, while Carbon-14, C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the Timeline of chemical element discoveries#Ancient discoveries, few elements known since antiquity. Carbon is the 15th Abundance of elements in Earth's crust, most abundant element in the Earth's crust, and the Abundance of the c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fatty Acid
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, from 4 to 28. Fatty acids are a major component of the lipids (up to 70% by weight) in some species such as microalgae but in some other organisms are not found in their standalone form, but instead exist as three main classes of esters: triglycerides, phospholipids, and cholesteryl esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and important structural components for cells. History The concept of fatty acid (''acide gras'') was introduced in 1813 by Michel Eugène Chevreul, though he initially used some variant terms: ''graisse acide'' and ''acide huileux'' ("acid fat" and "oily acid"). Types of fatty acids Fatty acids are classified in many ways: by length, by saturation vs unsaturati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphingosine
Sphingosine (2-amino-4-trans-octadecene-1,3-diol) is an 18-carbon amino alcohol with an unsaturated hydrocarbon chain, which forms a primary part of sphingolipids, a class of cell membrane lipids that include sphingomyelin, an important phospholipid. Functions Sphingosine can be phosphorylated in vivo via two kinases, sphingosine kinase type 1 and sphingosine kinase type 2. This leads to the formation of sphingosine-1-phosphate, a potent signaling lipid. Sphingolipid metabolites, such as ceramides, sphingosine and sphingosine-1-phosphate, are lipid signaling molecules involved in diverse cellular processes. Biosynthesis Sphingosine is synthesized from palmitoyl CoA and serine in a condensation required to yield dihydrosphingosine. Dehydrosphingosine is then reduced by NADPH to dihydrosphingosine (sphinganine), acylated to dihydroceramide finally oxidized by FAD to ceramide. Sphingosine is then solely formed via degradation of sphingolipid in the lysosome. See also * ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Proxy (climate)
In the study of past climates ("paleoclimatology"), climate proxies are preserved physical characteristics of the past that stand in for direct meteorological measurements and enable scientists to reconstruct the climatic conditions over a longer fraction of the Earth's history. Reliable global records of climate only began in the 1880s, and proxies provide the only means for scientists to determine climatic patterns before record-keeping began. A large number of climate proxies have been studied from a variety of geologic contexts. Examples of proxies include stable isotope measurements from ice cores, growth rates in tree rings, species composition of sub-fossil pollen in lake sediment or foraminifera in ocean sediments, temperature profiles of boreholes, and stable isotopes and mineralogy of corals and carbonate speleothems. In each case, the proxy indicator has been influenced by a particular seasonal climate parameter (e.g., summer temperature or monsoon intensity) at the t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glycerol Dialkyl Glycerol Tetraether
Glycerol dialkyl glycerol tetraether lipids (GDGTs) are a class of membrane lipids synthesized by archaea and some bacteria, making them useful biomarkers for these organisms in the geological record. Their presence, structure, and relative abundances in natural materials can be useful as proxies for temperature, terrestrial organic matter input, and soil pH for past periods in Earth history. Some structural forms of GDGT form the basis for the TEX86 paleothermometer. Isoprenoid GDGTs, now known to be synthesized by many archaeal classes, were first discovered in extremophilic archaea cultures. Branched GDGTs, likely synthesized by acidobacteriota, were first discovered in a natural Dutch peat sample in 2000. Chemical structure The two primary structural classes of GDGTs are isoprenoid (isoGDGT) and branched (brGDGT), which refer to differences in the carbon skeleton structures. Isoprenoid compounds are numbered -0 through -8, with the numeral representing the number of cyclopentan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
