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Esta estructura molecular es no polar. Por ejemplo la cera de abeja. Las vitaminas A, D, E y K son liposolubles, lo que significa que solo pueden ser digeridas, absorbidas y transportadas junto con las grasas.
Por ejemplo, las grasas poliinsaturadas y monoinsaturadas son analizadas de forma muy diferente. Liposoma — A liposome is a spherical vesicle having at least one lipid bilayer. The liposome can be used as a vehicle for administration of nutrients, liposomes can be prepared by disrupting biological membranes. A liposome design may employ surface ligands for attaching to unhealthy tissue, the major types of liposomes are the multilamellar vesicle, the small unilamellar liposome vesicle, the large unilamellar vesicle, and the cochleate vesicle.
A less desirable form are multivesicular liposomes in which one vesicle contains one or more smaller vesicles, liposomes should not be confused with micelles and reverse micelles composed of monolayers. The word liposome derives from two Greek words, lipo and soma, it is so named because its composition is primarily of phospholipid, liposomes were first described by British haematologist Alec D Bangham in , at the Babraham Institute, in Cambridge.
They were discovered when Bangham and R. Horne were testing the new electron microscope by adding negative stain to dry phospholipids. The resemblance to the plasmalemma was obvious, and the microscope pictures served as the first evidence for the membrane being a bilayer lipid structure. Their integrity as a closed, bilayer structure, that could release its contents after detergent treatment was established by Bangham, Standish, liposomes can be easily distinguished from micelles and hexagonal lipid phases by negative staining transmission electron microscopy.
It was Weissmann who proposed the more user-friendly term liposome, a liposome has an aqueous solution core surrounded by a hydrophobic membrane, in the form of a lipid bilayer, hydrophilic solutes dissolved in the core cannot readily pass through the bilayer. By preparing liposomes in a solution of DNA or drugs they can be delivered past the lipid bilayer, liposomes are used as models for artificial cells.
Liposomes can also be designed to deliver drugs in other ways, liposomes that contain low pH can be constructed such that dissolved aqueous drugs will be charged in solution. As the pH naturally neutralizes within the liposome, the drug will also be neutralized and these liposomes work to deliver drug by diffusion rather than by direct cell fusion. A similar approach can be exploited in the biodetoxification of drugs by injecting empty liposomes with a transmembrane pH gradient, in this case the vesicles act as sinks to scavenge the drug in the blood circulation and prevent its toxic effect.
Another strategy for drug delivery is to target endocytosis events. Liposomes can be made in a size range that makes them viable targets for natural macrophage phagocytosis. Micela — A micelle or micella is an aggregate of surfactant molecules dispersed in a liquid colloid.
A typical micelle in aqueous solution forms an aggregate with the hydrophilic head regions in contact with surrounding solvent and this phase is caused by the packing behavior of single-tail lipids in a bilayer. This type of micelle is known as a normal-phase micelle, inverse micelles have the head groups at the centre with the tails extending out. Micelles are approximately spherical in shape, other phases, including shapes such as ellipsoids, cylinders, and bilayers, are also possible.
The shape and size of a micelle are a function of the geometry of its surfactant molecules and solution conditions such as surfactant concentration, temperature, pH. The process of forming micelles is known as micellisation and forms part of the behaviour of many lipids according to their polymorphism. The ability of a solution to act as a detergent has been recognized for centuries. However, it is only at the beginning of the century that the constitution of such solutions was scientifically studied.
Individual surfactant molecules that are in the system but are not part of a micelle are called monomers, Micelles represent a molecular assembly, in which the individual components are thermodynamically in equilibrium with monomers of the same species in the surrounding medium. In water, the heads of surfactant molecules are always in contact with the solvent. However, the tails of surfactant molecules have less contact with water when they are part of a micelle—this being the basis for the energetic drive for micelle formation.
In a micelle, the tails of several surfactant molecules assemble into an oil-like core. By contrast, surfactant monomers are surrounded by water molecules that create a cage or solvation shell connected by hydrogen bonds and this water cage is similar to a clathrate and has an ice-like crystal structure and can be characterized according to the hydrophobic effect.
The extent of solubility is determined by the unfavorable entropy contribution due to the ordering of the water structure according to the hydrophobic effect. Micelles composed of ionic surfactants have an attraction to the ions that surround them in solution.
Although the closest counterions partially mask a charged micelle, the effects of micelle charge affect the structure of the surrounding solvent at appreciable distances from the micelle, ionic micelles influence many properties of the mixture, including its electrical conductivity. These membranes are flat sheets that form a barrier around all cells. The cell membranes of almost all living organisms and many viruses are made of a bilayer, as are the membranes surrounding the cell nucleus.
The lipid bilayer is the barrier that keeps ions, proteins and other molecules where they are needed, Lipid bilayers are ideally suited to this role because, even though they are only a few nanometers in width, they are impermeable to most water-soluble molecules.
Bilayers are particularly impermeable to ions, which allows cells to regulate salt concentrations, biological bilayers are usually composed of amphiphilic phospholipids that have a hydrophilic phosphate head and a hydrophobic tail consisting of two fatty acid chains. Phospholipids with certain groups can alter the surface chemistry of a bilayer and can, for example.
Just like the heads, the tails of lipids can also affect membrane properties, the packing of lipids within the bilayer also affects its mechanical properties, including its resistance to stretching and bending.
Many of these properties have been studied with the use of model bilayers produced in a lab. Vesicles made by model bilayers have also used clinically to deliver drugs. Biological membranes typically include several types of other than phospholipids. A particularly important example in animal cells is cholesterol, which strengthen the bilayer. Cholesterol also helps regulate the activity of certain integral membrane proteins, integral membrane proteins function when incorporated into a lipid bilayer, and they are held tightly to lipid bilayer with the help of an annular lipid shell.
Because bilayers define the boundaries of the cell and its compartments, certain kinds of membrane proteins are involved in the process of fusing two bilayers together. This fusion allows the joining of two structures as in the fertilization of an egg by sperm or the entry of a virus into a cell. Because lipid bilayers are quite fragile and invisible in a traditional microscope, experiments on bilayers often require advanced techniques like electron microscopy and atomic force microscopy.
When phospholipids are exposed to water, they self-assemble into a sheet with the hydrophobic tails pointing toward the center of the sheet. The assembly process is driven by interactions between hydrophobic molecules, an increase in interactions between hydrophobic molecules allows water molecules to bond more freely with each other, increasing the entropy of the system.
Organic compounds are rare terrestrially, but of importance because all known life is based on organic compounds. The most basic petrochemicals are considered the building blocks of organic chemistry, for historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates, simple oxides of carbon, and cyanides are considered inorganic. The distinction between organic and inorganic compounds, while useful in organizing the vast subject of chemistry.
Organic chemistry is the science concerned with all aspects of organic compounds, Organic synthesis is the methodology of their preparation. The word organic is historical, dating to the 1st century, for many centuries, Western alchemists believed in vitalism.
This is the theory that certain compounds could be synthesized only from their classical elements—earth, water, air, vitalism taught that these organic compounds were fundamentally different from the inorganic compounds that could be obtained from the elements by chemical manipulation.
Even though vitalism has been discredited, scientific nomenclature retains the distinction between organic and inorganic compounds, still, even the broadest definition requires excluding alloys that contain carbon, including steel. The C-H definition excludes compounds that are considered organic, neither urea nor oxalic acid is organic by this definition, yet they were two key compounds in the vitalism debate.
The IUPAC Blue Book on organic nomenclature specifically mentions urea and oxalic acid, other compounds lacking C-H bonds but traditionally considered organic include benzenehexol, mesoxalic acid, and carbon tetrachloride.
Mellitic acid, which contains no C-H bonds, is considered an organic substance in Martian soil. The C-H bond-only rule also leads to somewhat arbitrary divisions in sets of carbon-fluorine compounds, for example, CF4 would be considered by this rule to be inorganic, whereas CF3H would be organic.
Organic compounds may be classified in a variety of ways, one major distinction is between natural and synthetic compounds. Another distinction, based on the size of organic compounds, distinguishes between small molecules and polymers, natural compounds refer to those that are produced by plants or animals. Many of these are extracted from natural sources because they would be more expensive to produce artificially. Biomolecules are usually endogenous but may also be exogenous, for example, pharmaceutical drugs may be natural products or semisynthetic or they may be totally synthetic.
But many other elements, such as the various biometals, are present in small amounts, examples of these include cytidine, uridine, adenosine, guanosine, thymidine and inosine. Nucleosides can be phosphorylated by specific kinases in the cell, producing nucleotides, both DNA and RNA are polymers, consisting of long, linear molecules assembled by polymerase enzymes from repeating structural units, or monomers, of mononucleotides.
Each nucleotide is made of a nitrogenous base, a pentose. They contain carbon, nitrogen, oxygen, hydrogen and phosphorus and they serve as sources of chemical energy, participate in cellular signaling, and are incorporated into important cofactors of enzymatic reactions.
This is known as B-form DNA, and is overwhelmingly the most favorable and common state of DNA, its highly specific and stable base-pairing is the basis of reliable genetic information storage.
DNA can sometimes occur as single strands or as A-form or Z-form helices, RNA, in contrast, forms large and complex 3D tertiary structures reminiscent of proteins, as well as the loose single strands with locally folded regions that constitute messenger RNA molecules.
Those RNA structures contain many stretches of A-form double helix, connected into definite 3D arrangements by single-stranded loops, bulges, examples are tRNA, ribosomes, ribozymes, and riboswitches.
Monosaccharides are the simplest form of carbohydrates with only one simple sugar and they essentially contain an aldehyde or ketone group in their structure. The presence of an group in a monosaccharide is indicated by the prefix aldo-.
Similarly, a group is denoted by the prefix keto-. Examples of monosaccharides are the hexoses glucose, fructose, and galactose and pentoses, ribose, most saccharides eventually provide fuel for cellular respiration. Disaccharides are formed when two monosaccharides, or two simple sugars, form a bond with removal of water.
They can be hydrolyzed to yield their saccharin building blocks by boiling with dilute acid or reacting them with appropriate enzymes, examples of disaccharides include sucrose, maltose, and lactose. Carbono — Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds, three isotopes occur naturally, 12C and 13C being stable, while 14C is a radioactive isotope, decaying with a half-life of about 5, years.
Carbon is one of the few elements known since antiquity, Carbon is the 15th most abundant element in the Earths crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. It is the second most abundant element in the body by mass after oxygen. The atoms of carbon can bond together in different ways, termed allotropes of carbon, the best known are graphite, diamond, and amorphous carbon.
The physical properties of carbon vary widely with the allotropic form, for example, graphite is opaque and black while diamond is highly transparent.
Graphite is soft enough to form a streak on paper, while diamond is the hardest naturally occurring material known, graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials, all carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form.
The largest sources of carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil. For this reason, carbon has often referred to as the king of the elements. The allotropes of carbon graphite, one of the softest known substances, and diamond.
It bonds readily with other small atoms including other carbon atoms, Carbon is known to form almost ten million different compounds, a large majority of all chemical compounds. Carbon also has the highest sublimation point of all elements, although thermodynamically prone to oxidation, carbon resists oxidation more effectively than elements such as iron and copper that are weaker reducing agents at room temperature.
Carbon is the element, with a ground-state electron configuration of 1s22s22p2. Its first four ionisation energies, Carbons covalent radii are normally taken as Carbon compounds form the basis of all life on Earth. With a standard weight of circa 1. Its monatomic form is the most abundant chemical substance in the Universe, non-remnant stars are mainly composed of hydrogen in the plasma state.