Cholesterol is an organic molecule. It is a type of lipid. Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell membranes. Cholesterol 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 produce the greatest amounts, it is absent among prokaryotes, 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". There is only one kind of cholesterol. There is no "good cholesterol" or "bad cholesterol"; the system that transports cholesterol where it is needed in the human body uses LDL and HDL to do so. Those are proteins, not lipids like cholesterol, neither of them are "bad", both are necessary to human health.
Cholesterol is essential for all animal life, with each cell capable of synthesizing it by way of a complex 37-step process. This begins with the mevalonate or HMG-CoA reductase pathway, the target of statin drugs, which encompasses the first 18 steps; this is followed by 19 additional steps to convert the resulting lanosterol into cholesterol. A human male weighing 68 kg synthesizes about 1 gram of cholesterol per day, his body contains about 35 g contained within the cell membranes. Typical daily cholesterol dietary intake for a man in the United States is 307 mg. Most ingested cholesterol is esterified; the body compensates for absorption of ingested cholesterol by reducing its own cholesterol synthesis. For these reasons, cholesterol in food, seven to ten hours after ingestion, has little, if any effect on concentrations of cholesterol in the blood. However, during the first seven hours after ingestion of cholesterol, as absorbed fats are being distributed around the body within extracellular water by the various lipoproteins, the concentrations increase.
Cholesterol is recycled in the body. The liver excretes it in a non-esterified form into the digestive tract. About 50% of the excreted cholesterol is reabsorbed by the small intestine back into the bloodstream. Plants make cholesterol in small amounts. Plants manufacture phytosterols, which can compete with cholesterol for reabsorption in the intestinal tract, thus reducing cholesterol reabsorption; when intestinal lining cells absorb phytosterols, in place of cholesterol, they excrete the phytosterol molecules back into the GI tract, an important protective mechanism. The intake of occurring phytosterols, which encompass plant sterols and stanols, ranges between ~200–300 mg/day depending on eating habits. Specially designed vegetarian experimental diets have been produced yielding upwards of 700 mg/day. Cholesterol, given that it composes about 30% of all animal cell membranes, is required to build and maintain membranes and modulates membrane fluidity over the range of physiological temperatures.
The hydroxyl group of each cholesterol molecule interacts with the water molecules surrounding the membrane as do the polar heads of the membrane phospholipids and sphingolipids, while the bulky steroid and the hydrocarbon chain are embedded in the membrane, alongside the nonpolar fatty-acid chain of the other lipids. Through the interaction with the phospholipid fatty-acid chains, cholesterol increases membrane packing, which both alters membrane fluidity and maintains membrane integrity so that animal cells do not need to build cell walls; the membrane remains stable and durable without being rigid, allowing animal cells to change shape and animals to move. The structure of the tetracyclic ring of cholesterol contributes to the fluidity of the cell membrane, as the molecule is in a trans conformation making all but the side chain of cholesterol rigid and planar. In this structural role, cholesterol reduces the permeability of the plasma membrane to neutral solutes, hydrogen ions, sodium ions.
Within the cell membrane, cholesterol functions in intracellular transport, cell signaling and nerve conduction. Cholesterol is essential for the structure and function of invaginated caveolae and clathrin-coated pits, including caveola-dependent and clathrin-dependent endocytosis; the role of cholesterol in endocytosis of these types can be investigated by using methyl beta cyclodextrin to remove cholesterol from the plasma membrane. Recent studies show that cholesterol is implicated in cell signaling processes, assisting in the formation of lipid rafts in the plasma membrane, which brings receptor proteins in close proximity with high concentrations of second messenger molecules. In multiple layers and phospholipids, both electrical insulators, can facilitate speed of transmission of electrical impulses along nerve tissue. For many neuron fibers, a myelin sheath, rich in cholesterol since it is derived from compacted layers of Schwann cell membrane, provides insulation for more efficient conduction of impulses.
Demyelination is believed to be part of the basis for multiple sclerosis. Within cells, cholesterol is a precursor molecule for several biochemical pathways. For example, it is the precursor molecule for the synthesis of vitamin D and all steroid hormones, including the adrenal gland ho
In chemistry in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, either saturated or unsaturated. Most occurring fatty acids have an unbranched chain of an number of carbon atoms, from 4 to 28. Fatty acids are not found in organisms, but instead as three main classes of esters: triglycerides and cholesterol esters. In any of these forms, fatty acids are both important dietary sources of fuel for animals and they are important structural components for cells; the concept of fatty acid was introduced by Michel Eugène Chevreul, though he used some variant terms: graisse acide and acide huileux. Fatty acids differ by length categorized as short to long. Short-chain fatty acids are fatty acids with aliphatic tails of five or fewer carbons. Medium-chain fatty acids are fatty acids with aliphatic tails of 6 to 12 carbons, which can form medium-chain triglycerides. Long-chain fatty acids are fatty acids with aliphatic tails of 13 to 21 carbons. Long chain fatty acids are fatty acids with aliphatic tails of 22 or more carbons.
Saturated fatty acids have no C=C double bonds. They have the same formula CH3nCOOH, with variations in "n". An important saturated fatty acid is stearic acid, which when neutralized with lye is the most common form of soap. Unsaturated fatty acids have one or more C=C double bonds; the C=C double bonds can give either cis or trans isomers. Cis A cis configuration means that the two hydrogen atoms adjacent to the double bond stick out on the same side of the chain; the rigidity of the double bond freezes its conformation and, in the case of the cis isomer, causes the chain to bend and restricts the conformational freedom of the fatty acid. The more double bonds the chain has in the cis configuration, the less flexibility it has; when a chain has many cis bonds, it becomes quite curved in its most accessible conformations. For example, oleic acid, with one double bond, has a "kink" in it, whereas linoleic acid, with two double bonds, has a more pronounced bend. Α-Linolenic acid, with three double bonds, favors a hooked shape.
The effect of this is that, in restricted environments, such as when fatty acids are part of a phospholipid in a lipid bilayer, or triglycerides in lipid droplets, cis bonds limit the ability of fatty acids to be packed, therefore can affect the melting temperature of the membrane or of the fat. Trans A trans configuration, by contrast, means that the adjacent two hydrogen atoms lie on opposite sides of the chain; as a result, they do not cause the chain to bend much, their shape is similar to straight saturated fatty acids. In most occurring unsaturated fatty acids, each double bond has three n carbon atoms after it, for some n, all are cis bonds. Most fatty acids in the trans configuration are not found in nature and are the result of human processing; the differences in geometry between the various types of unsaturated fatty acids, as well as between saturated and unsaturated fatty acids, play an important role in biological processes, in the construction of biological structures. The position of the carbon atoms in a fatty acid can be indicated from the −COOH end, or from the −CH3 end.
If indicated from the −COOH end the C-1, C-2, C-3, …. Notation is used. If the position is counted from the other, −CH3, end the position is indicated by the ω-n notation; the positions of the double bonds in a fatty acid chain can, therefore, be indicated in two ways, using the C-n or the ω-n notation. Thus, in an 18 carbon fatty acid, a double bond between C-12 and C-13 is reported either as Δ12 if counted from the −COOH end, or as ω-6 if counting from the −CH3 end; the "Δ" is the Greek letter delta. Omega is the last letter in the Greek alphabet, is therefore used to indicate the “last” carbon atom in the fatty acid chain. Since the ω-n notation is used exclusively to indicate the positions of the double bonds close to the −CH3 end in essential fatty acids, there is no necessity for an equivalent “Δ”-like notation - the use of the “ω-n” notation always refers to the position of a double bond. Fatty acids with an odd number of carbon atoms are called odd-chain fatty acids, whereas the rest are even-chain fatty acids.
The difference is relevant to gluconeogenesis. The following table describes the most common systems of naming fatty acids; when circulating in the plasma are not in their ester, fatty acids are known as non-esterified fatty acids or free fatty acids. FFAs are always bound to a transport protein, such as albumin. Fatty acids are produced industrially by the hydrolysis of triglycerides, with the removal of glycerol. Phospholipids represent another source; some fatty acids are produced synthetically by hydrocarboxylation of alkenes. Template:Says whom? In animals, fatty acids are formed from carbohydrates predominantly in the liver, adipose tissue, the mammary glands during lactation. Carbohydrates are converted into pyruvate by glycolysis as the first important step in the conversion of carbohydrates into fatty acids. Pyruvate is decarboxylated to form acetyl-CoA in the mitochondrion. However, this acetyl CoA needs to be transported into cytosol where the synthesis of fatty acids occurs; this cannot occur directly.
To obtain cytosol
Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species the valves are calcified, many are somewhat irregular in shape. Many, but not all, oysters are in the superfamily Ostreoidea; some kinds of oysters are consumed cooked or raw and are regarded as a delicacy. Some kinds of pearl oysters are harvested for the pearl produced within the mantle. Windowpane oysters are harvested for their translucent shells, which are used to make various kinds of decorative objects. First attested in English during the 14th century, the word "oyster" comes from Old French oistre, in turn from Latin ostrea, the feminine form of ostreum, the latinisation of the Greek ὄστρεον, "oyster". Compare ὀστέον, "bone". True oysters are members of the family Ostreidae; this family includes the edible oysters, which belong to the genera Ostrea, Ostreola and Saccostrea. Examples include the Belon oyster, eastern oyster, Olympia oyster, Pacific oyster, the Sydney rock oyster.
All shell-bearing mollusks can secrete pearls, yet most are not valuable. Pearls can form in both freshwater environments. Pearl oysters are not related to true oysters, being members of a distinct family, the feathered oysters. Both cultured pearls and natural pearls can be extracted from pearl oysters, though other molluscs, such as the freshwater mussels yield pearls of commercial value; the largest pearl-bearing oyster is the marine Pinctada maxima, the size of a dinner plate. Not all individual oysters produce pearls naturally. In fact, in a harvest of two and a half tons of oysters, only three to four oysters produce what commercial buyers consider to be absolute perfect pearls. In nature, pearl oysters produce pearls by covering a minute invasive object with nacre. Over the years, the irritating object is covered with enough layers of nacre to become a pearl; the many different types and shapes of pearls depend on the natural pigment of the nacre, the shape of the original irritant. Pearl farmers can culture a pearl by placing a nucleus a piece of polished mussel shell, inside the oyster.
In three to seven years, the oyster can produce a perfect pearl. These pearls are not as valuable as natural pearls, but look the same. In fact, since the beginning of the 20th century, when several researchers discovered how to produce artificial pearls, the cultured pearl market has far outgrown the natural pearl market. A number of bivalve molluscs have common names that include the word "oyster" because they either taste like or look somewhat like true oysters, or because they yield noticeable pearls. Examples include: Thorny oysters in the genus Spondylus Pilgrim oyster, another term for a scallop, in reference to the scallop shell of St. James Saddle oysters, members of the Anomiidae family known as jingle shells Dimydarian oysters, members of the family Dimyidae Windowpane oysters In the Philippines, a local thorny oyster species known as Tikod Amo is a favorite seafood source in the southern part of the country; because of its good flavor, it commands high prices. Oysters are filter feeders.
Suspended plankton and particles are trapped in the mucus of a gill, from there are transported to the mouth, where they are eaten and expelled as feces or pseudofeces. Oysters feed most at temperatures above 10 °C. An oyster can filter up to 5 L of water per hour; the Chesapeake Bay's once-flourishing oyster population filtered excess nutrients from the estuary's entire water volume every three to four days. Today, that would take nearly a year. Excess sediment and algae can result in the eutrophication of a body of water. Oyster filtration can mitigate these pollutants. In addition to their gills, oysters can exchange gases across their mantles, which are lined with many small, thin-walled blood vessels. A small, three-chambered heart, lying under the adductor muscle, pumps colorless blood to all parts of the body. At the same time, two kidneys, located on the underside of the muscle, remove waste products from the blood, their nervous system includes three pairs of ganglia. While some oysters have two sexes, their reproductive organs contain sperm.
Because of this, it is technically possible for an oyster to fertilize its own eggs. The gonads surround the digestive organs, are made up of sex cells, branching tubules, connective tissue. Once the female is fertilized, she discharges millions of eggs into the water; the larvae develop in about six hours and exist suspended in the water column as veliger larvae for two to three weeks before settling on a bed and maturing to sexual adulthood within a year. A group of oysters is called a bed or oyster reef; as a keystone species, oysters provide habitat for many marine species. Crassostrea and Saccostrea live in the intertidal zone, while Ostrea is subtidal; the hard surfaces of oyster shells and the nooks between the shells provide places where a host of small animals can live. Hundreds of animals, such as sea anemones and hooked mussels, inhabit oyster reefs. Many of these animals are prey to larger animals, including fish, such as striped bass, black drum and croakers. An oyster reef can increase the surface area of a flat bottom 50-fold.
An oyster's mature shape depends on the type of bottom to which it is attached, but it always orients itself with its outer, flared shell tilted upward. One valve is cupped and t
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group on the periodic table, a reactive nonmetal, an oxidizing agent that forms oxides with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after helium. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O2. Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up half of the Earth's crust. Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids and fats, as do the major constituent inorganic compounds of animal shells and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide.
Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form of oxygen, ozone absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of thus a pollutant. Oxygen was isolated by Michael Sendivogius before 1604, but it is believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, Joseph Priestley in Wiltshire, in 1774. Priority is given for Priestley because his work was published first. Priestley, called oxygen "dephlogisticated air", did not recognize it as a chemical element; the name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and characterized the role it plays in combustion. Common uses of oxygen include production of steel and textiles, brazing and cutting of steels and other metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines and diving.
One of the first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium. In his work Pneumatica, Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in the vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration. In the late 17th century, Robert Boyle proved. English chemist John Mayow refined this work by showing that fire requires only a part of air that he called spiritus nitroaereus. In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects.
From this he surmised that nitroaereus is consumed in both combustion. Mayow observed that antimony increased in weight when heated, inferred that the nitroaereus must have combined with it, he thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke, Ole Borch, Mikhail Lomonosov, Pierre Bayen all produced oxygen in experiments in the 17th and the 18th century but none of them recognized it as a chemical element; this may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory, the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher, modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts.
One part, called phlogiston, was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx. Combustible materials that leave little residue, such as wood or coal, were thought to be made of phlogiston. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test the idea. Polish alchemist and physician Michael Sendivogius in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti described a substance contained in air, referring to it as'cibus vitae', this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by the thermal decomposition of potassium nitrate. In Bugaj’s view, the isolation of oxygen and the proper association of the substance to that part of air, required for life, lends sufficient weight to the discovery of oxygen by Sendivogius.
A drying oil is an oil that hardens to a tough, solid film after a period of exposure to air. The oil hardens through a chemical reaction in which the components crosslink by the action of oxygen. Drying oils are a key component of some varnishes; some used drying oils include linseed oil, tung oil, poppy seed oil, perilla oil, walnut oil. Their use has declined over the past several decades, as they have been replaced by alkyd resins and other binders. Since oxidation is the key to curing in these oils, those that are susceptible to chemical drying are unsuitable for cooking, are highly susceptible to becoming rancid through autoxidation, the process by which fatty foods develop off-flavors. Rags and paper saturated with drying oils may combust spontaneously after a few hours as heat is released during the oxidation process; the "drying", hardening, or, more properly, curing of oils is the result of autoxidation, the addition of oxygen to an organic compound and the subsequent crosslinking. This process begins with an oxygen molecule in the air inserting into carbon-hydrogen bonds adjacent to one of the double bonds within the unsaturated fatty acid.
The resulting hydroperoxides are susceptible to crosslinking reactions. Bonds form between neighboring fatty acid chains, resulting in a polymer network visible by formation of a skin-like film on samples; this polymerization results in stable films that, while somewhat elastic, do not flow or deform readily. Diene-containing fatty acid derivatives, such as those derived from linoleic acid, are prone to this reaction because they generate pentadienyl radicals. Monounsaturated fatty acids, such as oleic acid, are slower to undergo drying because the allylic radical intermediates are less stable; the early stages of the drying process can be monitored by weight changes in an oil film. The film becomes heavier. Linseed oil, for instance, increases in weight by 17 percent; as oxygen uptake ceases, the weight of the film declines. As the oil ages, further transitions occur. A large number of the original ester bonds in the oil molecules undergo hydrolysis, releasing individual fatty acids. In the case of paints, some portion of these free fatty acids react with metals in the pigment, producing metal carboxylates.
Together, the various non-cross-linking substances associated with the polymer network constitute the mobile phases. Unlike the molecules that are part of the network itself, they are capable of moving and diffusing within the film, can be removed using heat or a solvent; the mobile phase may play a role in plasticizing paint films, preventing them from becoming too brittle. Carboxyl groups in the polymers of the stationary phase ionize, becoming negatively charged and form complexes with metal cations present in the pigment; the original network, with its nonpolar, covalent bonds, is replaced by an ionomeric structure, held together by ionic interactions. The structure of these ionomeric networks is not well understood. Most drying oils increase in viscosity after heating in the absence of air. If the oil is subjected to raised temperatures for a long time, it will become a rubbery oil-insoluble substance; the drying process is accelerated by certain metal salts derivatives of cobalt, manganese, or iron.
In technical terms, these oil drying agents are coordination complexes that function as homogeneous catalysts. These salts are derived from the carboxylates of lipophilic carboxylic acids, such as naphthenic acids to make the complexes oil-soluble; these catalysts speed up the reduction of the hydroperoxide intermediates. A series of addition reactions ensues; each step produces additional free radicals, which engage in further crosslinking. The process terminates when pairs of free radicals combine; the polymerization renders the film dry to the touch. Premature action of the drying agents causes skinning of the paint, this undesirable process is suppressed by the addition of antiskinning agents such as methylethyl ketone oxime, which evaporate when the paint/oil is applied to a surface. Drying oils consist of glycerol triesters of fatty acids; these esters are characterized by high levels of polyunsaturated fatty acids alpha-linolenic acid. One common measure of the "siccative" property of oils is iodine number, an indicator of the number of double bonds in the oil.
Oils with an iodine number greater than 130 are considered drying, those with an iodine number of 115–130 are semi-drying, those with an iodine number of less than 115 are non-drying. Non-"drying" waxes, such as hard-film carnauba or paste wax, resins, such as dammar and shellac, consist of long, spaghetti-like strands of hydrocarbon molecules, which interlace and compact but do not form covalent bonds in the manner of drying oils, thus and resins are re-dissoluble whereas a cured oil varnish or paint is not. Rags and paper saturated with drying oils may combust spontaneously due to heat released during the curing process; this hazard is greater when oil-soaked materials are folded, bunched, or piled together, which allows heat to accumulate and accelerate the reaction. Precautions include: wetting rags with water and spreading them away from direct sunlight. Linseed oil soaked rags were the cause of the big fire in the One Meridian Plaza 38-storey office building resulted in severe structural damage
A carboxylic acid is an organic compound that contains a carboxyl group. The general formula of a carboxylic acid is R–COOH, with R referring to the rest of the molecule. Carboxylic acids occur widely. Important examples include acetic acid. Deprotonation of a carboxyl group gives a carboxylate anion. Important carboxylate salts are soaps. Carboxylic acids are identified by their trivial names, they have the suffix -ic acid. IUPAC-recommended names exist. For example, butyric acid is butanoic acid by IUPAC guidelines. For nomenclature of complex molecules containing a carboxylic acid, the carboxyl can be considered position one of the parent chain if there are other substituents, for example, 3-chloropropanoic acid. Alternately, it can be named as a "carboxy" or "carboxylic acid" substituent on another parent structure, for example, 2-carboxyfuran; the carboxylate anion of a carboxylic acid is named with the suffix -ate, in keeping with the general pattern of -ic acid and -ate for a conjugate acid and its conjugate base, respectively.
For example, the conjugate base of acetic acid is acetate. Carboxylic acids are polar; because they are both hydrogen-bond acceptors and hydrogen-bond donors, they participate in hydrogen bonding. Together the hydroxyl and carbonyl group forms the functional group carboxyl. Carboxylic acids exist as dimers in nonpolar media due to their tendency to "self-associate". Smaller carboxylic acids are soluble in water, whereas higher carboxylic acids have limited solubility due to the increasing hydrophobic nature of the alkyl chain; these longer chain acids tend to be rather soluble in less-polar solvents such as ethers and alcohols. Hydrophobic carboxylic acids react aqueous sodium hydroxide to give water soluble sodium salts. For example, enathic acid has a small solubility in water, but its sodium salt is soluble in water: Carboxylic acids tend to have higher boiling points than water, not only because of their increased surface area, but because of their tendency to form stabilised dimers through hydrogen bonds.
For boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporised, both of which increase the enthalpy of vaporization requirements significantly. Carboxylic acids are Brønsted -- Lowry acids, they are the most common type of organic acid. Carboxylic acids are weak acids, meaning that they only dissociate into H3O+ cations and RCOO− anions in neutral aqueous solution. For example, at room temperature, in a 1-molar solution of acetic acid, only 0.4% of the acid are dissociated. Electron-withdrawing substituents, such as -CF3 group, give stronger acids. Electron-donating substituents give weaker acids Deprotonation of carboxylic acids gives carboxylate anions; each of the carbon–oxygen bonds in the carboxylate anion has a partial double-bond character. The carbonyl carbon's partial positive charge is weakened by the -1/2 negative charges on the 2 oxygen atoms. Carboxylic acids have strong sour odors. Esters of carboxylic acids tend to have pleasant odors, many are used in perfume.
Carboxylic acids are identified as such by infrared spectroscopy. They exhibit a sharp band associated with vibration of the C–O vibration bond between 1680 and 1725 cm−1. A characteristic νO–H band appears as a broad peak in the 2500 to 3000 cm−1 region. By 1H NMR spectrometry, the hydroxyl hydrogen appears in the 10–13 ppm region, although it is either broadened or not observed owing to exchange with traces of water. Many carboxylic acids are produced industrially on a large scale, they are pervasive in nature. Esters of fatty acids are the main components of lipids and polyamides of aminocarboxylic acids are the main components of proteins. Carboxylic acids are used in the production of polymers, pharmaceuticals and food additives. Industrially important carboxylic acids include acetic acid and methacrylic acids, adipic acid, citric acid, ethylenediaminetetraacetic acid, fatty acids, maleic acid, propionic acid, terephthalic acid. In general, industrial routes to carboxylic acids differ from those used on smaller scale because they require specialized equipment.
Carbonylation of alcohols as illustrated by the Cativa process for production of acetic acid. Formic acid is prepared by a different carbonylation pathway starting from methanol. Oxidation of aldehydes with air using cobalt and manganese catalysts; the required aldehydes are obtained from alkenes by hydroformylation. Oxidation of hydrocarbons using air. For simple alkanes, this method is inexpensive but not selective enough to be useful. Allylic and benzylic compounds undergo more selective oxidations. Alkyl groups on a benzene ring are oxidized to the carboxylic acid, regardless of its chain length. Benzoic acid from toluene, terephthalic acid from para-xylene, phthalic acid from ortho-xylene are illustrative large-scale conversions. Acrylic acid is generated from propene. Base-cata
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