Metabolism

Metabolism (from Greek μεταβολισμός (metabolismós), "outthrow") is the set of chemical reactions that happen in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments(Akku Sony VAIO VGN-FZ31M). Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular respiration. Anabolism uses energy to construct components of cells such as proteins and nucleic acids(Akku Sony VAIO VGN-FZ31J).

The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, by a sequence of enzymes. Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy and will not occur by themselves(Akku Sony VAIO VGN-FZ31E), by coupling them to spontaneous reactions that release energy. As enzymes act as catalyststhey allow these reactions to proceed quickly and efficiently. Enzymes also allow the regulation of metabolic pathways in response to changes in the cell's environment or signals from other cells(Akku Sony VAIO VGN-FZ38M).

The metabolism of an organism determines which substances it will find nutritious and which it will find poisonous. For example, some prokaryotes usehydrogen sulfide as a nutrient, yet this gas is poisonous to animals. The speed of metabolism, the metabolic rate, also influences how much food an organism will require(Akku Sony VAIO VGN-FZ21Z).

A striking feature of metabolism is the similarity of the basic metabolic pathways and components between even vastly different species. For example, the set of carboxylic acids that are best known as the intermediates in the citric acid cycle are present in all organisms(Akku Sony VAIO VGN-FZ21S), being found in species as diverse as theunicellular bacteria Escherichia coli and huge multicellular organisms like elephants. These striking similarities in metabolic pathways are likely due to their early appearance in evolutionary history, and being retained because of their efficacy(Akku Sony VAIO VGN-FZ21M).

Key biochemicals

Most of the structures that make up animals, plants and microbes are made from three basic classes of molecule: amino acids, carbohydratesand lipids (often called fats). As these molecules are vital for life, metabolic reactions either focus on making these molecules during the construction of cells and tissues(Akku Sony VAIO VGN-FZ21J), or breaking them down and using them as a source of energy, in the digestion and use of food. Many important biochemicals can be joined together to make polymers such asDNA and proteins. These macromolecules are essential(Akku Sony VAIO VGN-FZ21E).

Amino acids and proteins

Proteins are made of amino acids arranged in a linear chain and joined together by peptide bonds. Many proteins are the enzymes that catalyzethe chemical reactions in metabolism. Other proteins have structural or mechanical functions(Akku Sony VAIO VGN-FZ140E), such as the proteins that form the cytoskeleton, a system of scaffolding that maintains the cell shape. Proteins are also important in cell signaling, immune responses, cell adhesion, active transport across membranes, and the cell cycle(Akku Sony VAIO VGN-FZ130E/B).

Lipids

Lipids are the most diverse group of biochemicals. Their main structural uses are as part of biological membranes such as the cell membrane, or as a source of energy. Lipids are usually defined as hydrophobicor amphipathic biological molecules that will dissolve in organic solventssuch as benzene or chloroform(Akku Sony VAIO VGN-FZ11Z). The fats are a large group of compounds that contain fatty acids and glycerol; a glycerol molecule attached to three fatty acid esters is a triacylglyceride. Several variations on this basic structure exist, including alternate backbones such as sphingosinein the sphingolipids(Akku Sony VAIO VGN-FZ11S), and hydrophilic groups such asphosphate in phospholipids. Steroids such as cholesterol are another major class of lipids that are made in cells.

Carbohydrates

Carbohydrates are straight-chain aldehydes or ketones with many hydroxyl groups that can exist as straight chains or rings(Akku Sony VAIO VGN-FZ11M). Carbohydrates are the most abundant biological molecules, and fill numerous roles, such as the storage and transport of energy (starch, glycogen) and structural components (cellulose in plants, chitin in animals). The basic carbohydrate units are called monosaccharides and include galactose, fructose, and most importantly glucose(Akku Sony VAIO VGN-FZ11L). Monosaccharides can be linked together to form polysaccharides in almost limitless ways.

Nucleotides

The two nucleic acids, DNA and RNA are polymers of nucleotides, each nucleotide comprising a phosphate group, a ribose sugar group, and a nitrogenous base. Nucleic acids are critical for the storage and use of genetic information, through the processes of transcription and protein biosynthesis(Sony VAIO VGN-FZ11E Battery). This information is protected by DNA repair mechanisms and propagated through DNA replication. Many viruses have an RNA genome, for example HIV, which uses reverse transcription to create a DNA template from its viral RNA genome(Akku Sony VGN-NR11Z/T). RNA in ribozymes such as spliceosomes and ribosomes is similar to enzymes as it can catalyze chemical reactions. Individual nucleosides are made by attaching a nucleobase to a ribose sugar. These bases are heterocyclic rings containing nitrogen, classified as purines orpyrimidines(Akku Sony VGN-NR11Z/S). Nucleotides also act as coenzymes in metabolic group transfer reactions.

Coenzymes

Metabolism involves a vast array of chemical reactions, but most fall under a few basic types of reactions that involve the transfer of functional groups. This common chemistry allows cells to use a small set of metabolic intermediates to carry chemical groups between different reactions(Akku Sony VGN-NR11S/S). These group-transfer intermediates are called coenzymes. Each class of group-transfer reaction is carried out by a particular coenzyme, which is the substrate for a set of enzymes that produce it, and a set of enzymes that consume it. These coenzymes are therefore continuously being made, consumed and then recycled(Akku Sony VGN-NR11M/S).

One central coenzyme is adenosine triphosphate (ATP), the universal energy currency of cells. This nucleotide is used to transfer chemical energy between different chemical reactions. There is only a small amount of ATP in cells, but as it is continuously regenerated, the human body can use about its own weight in ATP per day(Sony VAIO PCG-8Z2L Akku). ATP acts as a bridge between catabolism and anabolism, with catabolic reactions generating ATP and anabolic reactions consuming it. It also serves as a carrier of phosphate groups in phosphorylation reactions.

A vitamin is an organic compound needed in small quantities that cannot be made in the cells. In human nutrition, most vitamins function as coenzymes after modification(Sony VAIO PCG-8Z1L Akku); for example, all water-soluble vitamins are phosphorylated or are coupled to nucleotides when they are used in cells. Nicotinamide adenine dinucleotide (NADH), a derivative of vitamin B3 (niacin), is an important coenzyme that acts as a hydrogen acceptor. Hundreds of separate types of dehydrogenases remove electrons from their substrates and reduce NAD+ into NADH(Sony VAIO PCG-8Y2L Akku). This reduced form of the coenzyme is then a substrate for any of the reductases in the cell that need to reduce their substrates. Nicotinamide adenine dinucleotide exists in two related forms in the cell, NADH and NADPH. The NAD+/NADH form is more important in catabolic reactions, while NADP+/NADPH is used in anabolic reactions(Sony VAIO PCG-8Y1L Akku).

Minerals and cofactors

Inorganic elements play critical roles in metabolism; some are abundant (e.g. sodium and potassium) while others function at minute concentrations. About 99% of mammals' mass are the elements carbon, nitrogen, calcium, sodium, chlorine, potassium(Sony VAIO PCG-7z1L Akku), hydrogen, phosphorus, oxygen and sulfur. The organic compounds(proteins, lipids and carbohydrates) contain the majority of the carbon and nitrogen and most of the oxygen and hydrogen is present as water.

The abundant inorganic elements act as ionic electrolytes(Sony VAIO PCG-7z1L Akku). The most important ions are sodium, potassium, calcium, magnesium, chloride, phosphate, and the organic ion bicarbonate. The maintenance of precise gradientsacross cell membranes maintains osmotic pressure and pH(Sony VAIO PCG-7133L Akku). Ions are also critical fornerves and muscles, as action potentials in these tissues are produced by the exchange of electrolytes between the extracellular fluid and the cytosol. Electrolytes enter and leave cells through proteins in the cell membrane called ion channels(Sony VAIO PCG-7132L Akku). For example, muscle contraction depends upon the movement of calcium, sodium and potassium through ion channels in the cell membrane and T-tubules.

The transition metals are usually present as trace elements in organisms, with zinc and iron being most abundant. These metals are used in some proteins as cofactors and are essential for the activity of enzymes such as catalase and oxygen-carrier proteins such as hemoglobin(Sony VAIO PCG-7131L Akku). These cofactors are bound tightly to a specific protein; although enzyme cofactors can be modified during catalysis, cofactors always return to their original state after catalysis has taken place(Sony VAIO PCG-7113L Akku). The metal micronutrients are taken up into organisms by specific transporters and bound to storage proteins such as ferritin ormetallothionein when not being used.

Catabolism

Catabolism is the set of metabolic processes that break down large molecules. These include breaking down and oxidizing food molecules. The purpose of the catabolic reactions is to provide the energy and components needed by anabolic reactions(Sony VAIO PCG-7112L Akku). The exact nature of these catabolic reactions differ from organism to organism and organisms can be classified based on their sources of energy and carbon (theirprimary nutritional groups), as shown in the table below. Organic molecules being used as a source of energy in organotrophs, while lithotrophs use inorganic substrates and phototrophs capture sunlight aschemical energy(Sony VAIO PCG-7111L Akku). However, all these different forms of metabolism depend on redoxreactions that involve the transfer of electrons from reduced donor molecules such as organic molecules, water, ammonia,hydrogen sulfideor ferrous ions to acceptor molecules such as oxygen, nitrate or sulfate(Sony VAIO PCG-6W3L Akku). In animals these reactions involve complex organic molecules being broken down to simpler molecules, such as carbon dioxide and water. In photosynthetic organisms such as plants and cyanobacteria, these electron-transfer reactions do not release energy, but are used as a way of storing energy absorbed from sunlight(Sony VAIO PCG-6W2L Akku).

The most common set of catabolic reactions in animals can be separated into three main stages. In the first, large organic molecules such as proteins, polysaccharides or lipids are digested into their smaller components outside cells. Next, these smaller molecules are taken up by cells and converted to yet smaller molecules(Sony VAIO PCG-6W1L Akku), usually acetyl coenzyme A (acetyl-CoA), which releases some energy. Finally, the acetyl group on the CoA is oxidised to water and carbon dioxide in the citric acid cycle and electron transport chain, releasing the energy that is stored by reducing the coenzyme nicotinamide adenine dinucleotide(NAD+) into NADH(Sony VAIO PCG-6S2L Akku).

Digestion

Macromolecules such as starch, cellulose or proteins cannot be rapidly taken up by cells and need to be broken into their smaller units before they can be used in cell metabolism. Several common classes of enzymes digest these polymers. These digestive enzymes include proteases that digest proteins into amino acids(Sony VAIO PCG-6S1L Akku), as well as glycoside hydrolases that digest polysaccharides into monosaccharides.

Microbes simply secrete digestive enzymes into their surroundings, while animals only secrete these enzymes from specialized cells in their guts. The amino acids or sugars released by these extracellular enzymes are then pumped into cells by specific active transportproteins(Sony VAIO PCG-5K1L Akku).

Energy from organic compounds

Carbohydrate catabolism is the breakdown of carbohydrates into smaller units. Carbohydrates are usually taken into cells once they have been digested intomonosaccharides. Once inside, the major route of breakdown is glycolysis, where sugars such as glucose and fructose are converted into pyruvate and some ATP is generated(Sony VAIO PCG-5K2L Akku). Pyruvate is an intermediate in several metabolic pathways, but the majority is converted to acetyl-CoA and fed into the citric acid cycle. Although some more ATP is generated in the citric acid cycle, the most important product is NADH, which is made from NAD+ as the acetyl-CoA is oxidized. This oxidation releases carbon dioxide as a waste product(Sony VAIO PCG-5J2L Akku). In anaerobic conditions, glycolysis produces lactate, through the enzyme lactate dehydrogenase re-oxidizing NADH to NAD+ for re-use in glycolysis. An alternative route for glucose breakdown is the pentose phosphate pathway, which reduces the coenzyme NADPH and produces pentose sugars such as ribose, the sugar component of nucleic acids(Sony VAIO PCG-5J1L Akku).

Fats are catabolised by hydrolysis to free fatty acids and glycerol. The glycerol enters glycolysis and the fatty acids are broken down by beta oxidation to release acetyl-CoA, which then is fed into the citric acid cycle. Fatty acids release more energy upon oxidation than carbohydrates because carbohydrates contain more oxygen in their structures(AKKU Sony VAIO PCG-5G3L ).

Amino acids are either used to synthesize proteins and other biomolecules, or oxidized to urea and carbon dioxide as a source of energy. The oxidation pathway starts with the removal of the amino group by a transaminase. The amino group is fed into the urea cycle, leaving a deaminated carbon skeleton in the form of a keto acid(AKKU Sony VAIO PCG-5G2L). Several of these keto acids are intermediates in the citric acid cycle, for example the deamination of glutamate forms α-ketoglutarate. The glucogenic amino acids can also be converted into glucose, through gluconeogenesis(discussed below) (AKKU Sony VAIO VGN-FW32Z).

Energy transformations

Oxidative phosphorylation

In oxidative phosphorylation, the electrons removed from organic molecules in areas such as the protagon acid cycle are transferred to oxygen and the energy released is used to make ATP. This is done in eukaryotes by a series of proteins in the membranes of mitochondria called the electron transport chain. Inprokaryotes(AKKU Sony VAIO VGN-FW31ZJ), these proteins are found in the cell's inner membrane. These proteins use the energy released from passing electrons from reduced molecules like NADH onto oxygen to pump protons across a membrane.

Pumping protons out of the mitochondria creates a proton concentration difference across the membrane and generates an electrochemical gradient(AKKU Sony VAIO VGN-FW31Z). This force drives protons back into the mitochondrion through the base of an enzyme called ATP synthase. The flow of protons makes the stalk subunit rotate, causing the active site of the synthase domain to change shape and phosphorylate adenosine diphosphate - turning it into ATP(AKKU Sony VAIO VGN-FW31E).

Energy from inorganic compounds

Chemolithotrophy is a type of metabolism found in prokaryotes where energy is obtained from the oxidation of inorganic compounds. These organisms can usehydrogen, reduced sulfur compounds (such as sulfide, hydrogen sulfide and thiosulfate) (AKKU Sony VAIO VGN-FW31J), ferrous iron (FeII) or ammonia as sources of reducing power and they gain energy from the oxidation of these compounds with electron acceptors such as oxygen or nitrite. These microbial processes are important in global biogeochemical cycles such as acetogenesis, nitrificationand denitrification and are critical for soil fertility(AKKU Sony VAIO VGN-FW31M).

Energy from light

The energy in sunlight is captured by plants, cyanobacteria, purple bacteria, green sulfur bacteria and some protists. This process is often coupled to the conversion of carbon dioxide into organic compounds, as part of photosynthesis, which is discussed below(AKKU Sony VAIO VGN-FW21M). The energy capture and carbon fixation systems can however operate separately in prokaryotes, as purple bacteria and green sulfur bacteria can use sunlight as a source of energy, while switching between carbon fixation and the fermentation of organic compounds(AKKU Sony VAIO VGN-FW21Z).

In many organisms the capture of solar energy is similar in principle to oxidative phosphorylation, as it involves energy being stored as a proton concentration gradient and this proton motive force then driving ATP synthesis(AKKU Sony VAIO VGN-FW21L). The electrons needed to drive this electron transport chain come from light-gathering proteins called photosynthetic reaction centres or rhodopsins. Reaction centers are classed into two types depending on the type of photosynthetic pigment present, with most photosynthetic bacteria only having one type, while plants and cyanobacteria have two(AKKU Sony VAIO VGN-FW21I).

In plants, algae, and cyanobacteria, photosystem II uses light energy to remove electrons from water, releasing oxygen as a waste product. The electrons then flow to the cytochrome b6f complex, which uses their energy to pump protons across the thylakoid membrane in the chloroplast(AKKU sony VAIO VGN-FW21E). These protons move back through the membrane as they drive the ATP synthase, as before. The electrons then flow throughphotosystem I and can then either be used to reduce the coenzyme NADP+, for use in the Calvin cycle which is discussed below, or recycled for further ATP generation(Akku Sony VGP-BPS14/B ).

Anabolism

Anabolism is the set of constructive metabolic processes where the energy released by catabolism is used to synthesize complex molecules. In general, the complex molecules that make up cellular structures are constructed step-by-step from small and simple precursors. Anabolism involves three basic stages(Akku Sony VGP-BPL14/B). Firstly, the production of precursors such as amino acids, monosaccharides, isoprenoids and nucleotides, secondly, their activation into reactive forms using energy from ATP, and thirdly, the assembly of these precursors into complex molecules such as proteins, polysaccharides, lipids and nucleic acids(Akku Sony VGP-BPS14/S ).

Organisms differ in how many of the molecules in their cells they can construct for themselves. Autotrophs such as plants can construct the complex organic molecules in cells such as polysaccharides and proteins from simple molecules like carbon dioxide and water. Heterotrophs, on the other hand( Akku Sony VGP-BPL14 ), require a source of more complex substances, such as monosaccharides and amino acids, to produce these complex molecules. Organisms can be further classified by ultimate source of their energy: photoautotrophs and photoheterotrophs obtain energy from light, whereas chemoautotrophs and chemoheterotrophs obtain energy from inorganic oxidation reactions(Akku Sony VGP-BPL14).

Carbon fixation

Photosynthesis is the synthesis of carbohydrates from sunlight and carbon dioxide (CO2). In plants, cyanobacteria and algae, oxygenic photosynthesis splits water, with oxygen produced as a waste product. This process uses the ATP and NADPH produced by the photosynthetic reaction centres(Sony VGP-BPS21/S Akku), as described above, to convert CO2 intoglycerate 3-phosphate, which can then be converted into glucose. This carbon-fixation reaction is carried out by the enzyme RuBisCO as part of the Calvin – Benson cycle. Three types of photosynthesis occur in plants, C3 carbon fixation, C4 carbon fixation and CAM photosynthesis(Sony VGP-BPS21A/B Akku). These differ by the route that carbon dioxide takes to the Calvin cycle, with C3 plants fixing CO2 directly, while C4 and CAM photosynthesis incorporate the CO2 into other compounds first, as adaptations to deal with intense sunlight and dry conditions(Sony VGP-BPS21B Akku).

In photosynthetic prokaryotes the mechanisms of carbon fixation are more diverse. Here, carbon dioxide can be fixed by the Calvin – Benson cycle, a reversed citric acidcycle, or the carboxylation of acetyl-CoA. Prokaryotic chemoautotrophs also fix CO2 through the Calvin – Benson cycle, but use energy from inorganic compounds to drive the reaction(Sony VGP-BPS21A Akku).

Carbohydrates and glycans

In carbohydrate anabolism, simple organic acids can be converted into monosaccharides such as glucose and then used to assemble polysaccharides such as starch. The generation of glucose from compounds like pyruvate, lactate, glycerol, glycerate 3-phosphateand amino acids is called gluconeogenesis(Sony VGP-BPS21 Akku). Gluconeogenesis converts pyruvate to glucose-6-phosphate through a series of intermediates, many of which are shared with glycolysis. However, this pathway is not simply glycolysis run in reverse, as several steps are catalyzed by non-glycolytic enzymes(Sony VGP-BPL9 Akku). This is important as it allows the formation and breakdown of glucose to be regulated separately and prevents both pathways from running simultaneously in a futile cycle.

Although fat is a common way of storing energy, in vertebrates such as humans the fatty acids in these stores cannot be converted to glucose through gluconeogenesis as these organisms cannot convert acetyl-CoA into pyruvate(Sony VGP-BPL9A Akku); plants do, but animals do not, have the necessary enzymatic machinery. As a result, after long-term starvation, vertebrates need to produce ketone bodies from fatty acids to replace glucose in tissues such as the brain that cannot metabolize fatty acids. In other organisms such as plants and bacteria(Sony VGP-BPL9A/B Akku), this metabolic problem is solved using the glyoxylate cycle, which bypasses the decarboxylationstep in the citric acid cycle and allows the transformation of acetyl-CoA to oxaloacetate, where it can be used for the production of glucose(Sony VGP-BPL9/S Akku).

Polysaccharides and glycans are made by the sequential addition of monosaccharides by glycosyltransferase from a reactive sugar-phosphate donor such as uridine diphosphate glucose (UDP-glucose) to an acceptor hydroxyl group on the growing polysaccharide(Sony VGP-BPL9/B Akku). As any of the hydroxylgroups on the ring of the substrate can be acceptors, the polysaccharides produced can have straight or branched structures. The polysaccharides produced can have structural or metabolic functions themselves, or be transferred to lipids and proteins by enzymes called oligosaccharyltransferases(Sony VGP-BPL9 Akku).

Fatty acids, isoprenoids and steroids

Fatty acids are made by fatty acid synthases that polymerize and then reduce acetyl-CoA units. The acyl chains in the fatty acids are extended by a cycle of reactions that add the actyl group, reduce it to an alcohol, dehydrate it to an alkene group and then reduce it again to an alkane group(Sony VGN-FZ130E/BB Battery). The enzymes of fatty acid biosynthesis are divided into two groups, in animals and fungi all these fatty acid synthase reactions are carried out by a single multifunctional type I protein, while in plant plastids and bacteria separate type II enzymes perform each step in the pathway(Sony VGN-FZ130E/BA Battery).

Terpenes and isoprenoids are a large class of lipids that include the carotenoids and form the largest class of plant natural products. These compounds are made by the assembly and modification of isoprene units donated from the reactive precursors isopentenyl pyrophosphateanddimethylallyl pyrophosphate(Sony VGN-FZ130E/B Battery). These precursors can be made in different ways. In animals and archaea, the mevalonate pathwayproduces these compounds from acetyl-CoA, while in plants and bacteria the non-mevalonate pathway uses pyruvate and glyceraldehyde 3-phosphate as substrates(Sony VGP-BPL8A Battery). One important reaction that uses these activated isoprene donors is steroid biosynthesis. Here, the isoprene units are joined together to make squalene and then folded up and formed into a set of rings to make lanosterol. Lanosterol can then be converted into other steroids such as cholesterol and ergosterol(Sony VGP-BPL8 Battery).

Proteins

Organisms vary in their ability to synthesize the 20 common amino acids. Most bacteria and plants can synthesize all twenty, but mammals can synthesize only eleven nonessential amino acids. Thus, nine essential amino acids must be obtained from food. All amino acids are synthesized from intermediates in glycolysis(AKKU Sony VGP-BPS13Q), the citric acid cycle, or the pentose phosphate pathway. Nitrogen is provided by glutamateand glutamine. Amino acid synthesis depends on the formation of the appropriate alpha-keto acid, which is then transaminated to form an amino acid(AKKU Sony VGP-BPS13B/Q).

Amino acids are made into proteins by being joined together in a chain by peptide bonds. Each different protein has a unique sequence of amino acid residues: this is its primary structure. Just as the letters of the alphabet can be combined to form an almost endless variety of words(AKKU Sony VGP-BPS13A/Q), amino acids can be linked in varying sequences to form a huge variety of proteins. Proteins are made from amino acids that have been activated by attachment to a transfer RNA molecule through an ester bond. This aminoacyl-tRNA precursor is produced in an ATP-dependent reaction carried out by an aminoacyl tRNA synthetase(AKKU Sony VGP-BPS13A/S). This aminoacyl-tRNA is then a substrate for the ribosome, which joins the amino acid onto the elongating protein chain, using the sequence information in a messenger RNA.

Nucleotide synthesis and salvage

Nucleotides are made from amino acids, carbon dioxide and formic acid in pathways that require large amounts of metabolic energy(AKKU Sony VGP-BPS13B/S). Consequently, most organisms have efficient systems to salvage preformed nucleotides. Purines are synthesized as nucleosides (bases attached to ribose). Both adenine and guanine are made from the precursor nucleoside inosine monophosphate, which is synthesized using atoms from the amino acids glycine, glutamine(AKKU Sony VGP-BPS13/S), and aspartic acid, as well as formate transferred from the coenzymetetrahydrofolate. Pyrimidines, on the other hand, are synthesized from the base orotate, which is formed from glutamine and aspartate.

Xenobiotics and redox metabolism

All organisms are constantly exposed to compounds that they cannot use as foods and would be harmful if they accumulated in cells(AKKU Sony VGP-BPS13B/B), as they have no metabolic function. These potentially damaging compounds are called xenobiotics. Xenobiotics such as synthetic drugs, natural poisons and antibiotics are detoxified by a set of xenobiotic-metabolizing enzymes. In humans, these include cytochrome P450 oxidases(AKKU Sony VGP-BPS13A/B), UDP-glucuronosyltransferases, and glutathione S-transferases. This system of enzymes acts in three stages to firstly oxidize the xenobiotic (phase I) and then conjugate water-soluble groups onto the molecule (phase II). The modified water-soluble xenobiotic can then be pumped out of cells and in multicellular organisms may be further metabolized before being excreted (phase III) (AKKU Sony VGP-BPS13). In ecology, these reactions are particularly important in microbial biodegradation of pollutants and the bioremediation of contaminated land and oil spills. Many of these microbial reactions are shared with multicellular organisms, but due to the incredible diversity of types of microbes these organisms are able to deal with a far wider range of xenobiotics than multicellular organisms, and can degrade even persistent organic pollutants such asorganochloride compounds(SONY VGP-BPS8 battery).

A related problem for aerobic organisms is oxidative stress. Here, processes including oxidative phosphorylation and the formation of disulfide bonds during protein folding produce reactive oxygen species such as hydrogen peroxide. These damaging oxidants are removed by antioxidant metabolites such as glutathione and enzymes such as catalases and peroxidases(SONY VAIO VGN-FZ Battery).

Thermodynamics of living organisms

Living organisms must obey the laws of thermodynamics, which describe the transfer of heat and work. The second law of thermodynamics states that in any closed system, the amount of entropy (disorder) will tend to increase. Although living organisms' amazing complexity appears to contradict this law(SONY VAIO VGN-FZ11S Battery), life is possible as all organisms are open systems that exchange matter and energy with their surroundings. Thus living systems are not in equilibrium, but instead are dissipative systems that maintain their state of high complexity by causing a larger increase in the entropy of their environments(SONY vgp-bps9 battery). The metabolism of a cell achieves this by coupling the spontaneous processes of catabolism to the non-spontaneous processes of anabolism. In thermodynamic terms, metabolism maintains order by creating disorder.

Regulation and control

As the environments of most organisms are constantly changing, the reactions of metabolism must be finely regulated to maintain a constant set of conditions within cells(sony vgp-bpl9 battery), a condition called homeostasis. Metabolic regulation also allows organisms to respond to signals and interact actively with their environments. Two closely linked concepts are important for understanding how metabolic pathways are controlled. Firstly, the regulation of an enzyme in a pathway is how its activity is increased and decreased in response to signals(SONY VAIO VGN-FZ32 Battery). Secondly, the controlexerted by this enzyme is the effect that these changes in its activity have on the overall rate of the pathway (the flux through the pathway). For example, an enzyme may show large changes in activity (i.e. it is highly regulated) but if these changes have little effect on the flux of a metabolic pathway, then this enzyme is not involved in the control of the pathway(SONY VAIO VGN-FZ440N Battery).

There are multiple levels of metabolic regulation. In intrinsic regulation, the metabolic pathway self-regulates to respond to changes in the levels of substrates or products; for example, a decrease in the amount of product can increase the flux through the pathway to compensate(SONY VAIO VGN-FZ280E Battery). This type of regulation often involves allosteric regulation of the activities of multiple enzymes in the pathway. Extrinsic control involves a cell in a multicellular organism changing its metabolism in response to signals from other cells. These signals are usually in the form of soluble messengers such as hormones and growth factors and are detected by specific receptors on the cell surface(SONY VAIO VGN-FZ460E Battery). These signals are then transmitted inside the cell by second messenger systems that often involved the phosphorylation of proteins.

A very well understood example of extrinsic control is the regulation of glucose metabolism by the hormone insulin. Insulin is produced in response to rises in blood glucose levels. Binding of the hormone to insulin receptors on cells then activates a cascade of protein kinases that cause the cells to take up glucose and convert it into storage molecules such as fatty acids and glycogen(SONY VAIO VGN-FZ190 Battery). The metabolism of glycogen is controlled by activity of phosphorylase, the enzyme that breaks down glycogen, and glycogen synthase, the enzyme that makes it. These enzymes are regulated in a reciprocal fashion, with phosphorylation inhibiting glycogen synthase, but activating phosphorylase(SONY VAIO VGN-FZ150E Battery). Insulin causes glycogen synthesis by activating protein phosphatases and producing a decrease in the phosphorylation of these enzymes.

Evolution

The central pathways of metabolism described above, such as glycolysis and the citric acid cycle, are present in all three domains of living things and were present in the last universal ancestor(SONY VAIO VGN-FZ260E Battery). This universal ancestral cell was prokaryotic and probably a methanogen that had extensive amino acid, nucleotide, carbohydrate and lipid metabolism. The retention of these ancient pathways during laterevolutionmay be the result of these reactions being an optimal solution to their particular metabolic problems(SONY VAIO VGN-FZ140E Battery), with pathways such as glycolysis and the citric acid cycle producing their end products highly efficiently and in a minimal number of steps. Mutation changes that affect non-coding DNA segments may merely affect the metabolic efficiency of the individual for whom the mutation occurs(SONY VAIO VGN-FZ11l Battery). The first pathways of enzyme-based metabolism may have been parts of purine nucleotide metabolism, with previous metabolic pathways being part of the ancient RNA world.

Many models have been proposed to describe the mechanisms by which novel metabolic pathways evolve. These include the sequential addition of novel enzymes to a short ancestral pathway, the duplication and then divergence of entire pathways as well as the recruitment of pre-existing enzymes and their assembly into a novel reaction pathway(SONY VAIO VGN-FZ11z Battery). The relative importance of these mechanisms is unclear, but genomic studies have shown that enzymes in a pathway are likely to have a shared ancestry, suggesting that many pathways have evolved in a step-by-step fashion with novel functions being created from pre-existing steps in the pathway. An alternative model comes from studies that trace the evolution of proteins' structures in metabolic networks(SONY VAIO VGN-FZ11m Battery), this has suggested that enzymes are pervasively recruited, borrowing enzymes to perform similar functions in different metabolic pathways (evident in the MANET database) These recruitment processes result in an evolutionary enzymatic mosaic. A third possibility is that some parts of metabolism might exist as "modules" that can be reused in different pathways and perform similar functions on different molecules(SONY VAIO VGN-FZ18m Battery).

As well as the evolution of new metabolic pathways, evolution can also cause the loss of metabolic functions. For example, in someparasitesmetabolic processes that are not essential for survival are lost and preformed amino acids, nucleotides and carbohydrates may instead be scavenged from the host. Similar reduced metabolic capabilities are seen in endosymbiotic organisms(SONY VAIO VGN-FZ21m Battery).

Investigation and manipulation

Classically, metabolism is studied by a reductionist approach that focuses on a single metabolic pathway. Particularly valuable is the use of radioactive tracers at the whole-organism, tissue and cellular levels, which define the paths from precursors to final products by identifying radioactively labelled intermediates and products(SONY VAIO VGN-FZ410 Battery). The enzymes that catalyze these chemical reactions can then be purified and their kinetics and responses to inhibitorsinvestigated. A parallel approach is to identify the small molecules in a cell or tissue; the complete set of these molecules is called the metabolome(SONY VAIO VGN-FZ21 Battery). Overall, these studies give a good view of the structure and function of simple metabolic pathways, but are inadequate when applied to more complex systems such as the metabolism of a complete cell.

An idea of the complexity of the metabolic networks in cells that contain thousands of different enzymes is given by the figure showing the interactions between just 43 proteins and 40 metabolites to the right(SONY VAIO VGN-FZ160 Battery): the sequences of genomes provide lists containing anything up to 45,000 genes. However, it is now possible to use this genomic data to reconstruct complete networks of biochemical reactions and produce more holistic mathematical models that may explain and predict their behavior(SONY VAIO VGN-FZ210CE Battery). These models are especially powerful when used to integrate the pathway and metabolite data obtained through classical methods with data on gene expression from proteomic and DNA microarray studies. Using these techniques, a model of human metabolism has now been produced(SONY VAIO VGN-FZ38M Battery), which will guide future drug discovery and biochemical research. These models are now being used in network analysis, to classify human diseases into groups that share common proteins or metabolites.

Bacterial metabolic networks seem to be a striking example of bow-tie organization, an architecture able to input a wide range of nutrients and produce a large variety of products and complex macromolecules using a relatively few intermediate common currencies(SONY VAIO VGN-FZ31z Battery).

A major technological application of this information is metabolic engineering. Here, organisms such as yeast, plants or bacteria are genetically modified to make them more useful in biotechnology and aid the production of drugs such as antibiotics or industrial chemicals such as 1,3-propanediol and shikimic acid(Sony Vaio VGN-FZ31S battery). These genetic modifications usually aim to reduce the amount of energy used to produce the product, increase yields and reduce the production of wastes.

History

The term metabolism is derived from the Greek Μεταβολισμός – "Metabolismos" for "change", or "overthrow"(SONY VAIO VGN-FZ31E Battery). The history of the scientific study of metabolism spans several centuries and has moved from examining whole animals in early studies, to examining individual metabolic reactions in modern biochemistry(SONY VAIO VGN-FZ31J Battery). The first controlled experiments in human metabolism were published by Santorio Santorio in 1614 in his book Ars de statica medicina. He described how he weighed himself before and after eating, sleep, working, sex, fasting, drinking, and excreting. He found that most of the food he took in was lost through what he called "insensible perspiration"(SONY VAIO VGN-FZ31M Battery).

In these early studies, the mechanisms of these metabolic processes had not been identified and a vital force was thought to animate living tissue. In the 19th century, when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that fermentation was catalyzed by substances within the yeast cells he called "ferments"(SONY VAIO VGN-FZ31B Battery). He wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells." This discovery, along with the publication by Friedrich Wohler in 1828 of the chemical synthesis of urea, proved that the organic compounds and chemical reactions found in cells were no different in principle than any other part of chemistry(HP PAVILION DV6000 battery).

It was the discovery of enzymes at the beginning of the 20th century by Eduard Buchner that separated the study of the chemical reactions of metabolism from the biological study of cells, and marked the beginnings of biochemistry. The mass of biochemical knowledge grew rapidly throughout the early 20th century(SONY VGP-BPS13 Battery). One of the most prolific of these modern biochemists was Hans Krebs who made huge contributions to the study of metabolism. He discovered the urea cycle and later, working with Hans Kornberg, the citric acid cycle and the glyoxylate cycle(SONY VGP-BPS13B/B Battery). Modern biochemical research has been greatly aided by the development of new techniques such as chromatography, X-ray diffraction, NMR spectroscopy, radioisotopic labelling, electron microscopy and molecular dynamics simulations. These techniques have allowed the discovery and detailed analysis of the many molecules and metabolic pathways in cells(ASUS EEE PC battery).

Lottery And Stock

Shares

The stock of a business is divided into shares, the total of which must be stated at the time of business formation. Given the total amount of money invested in the business, a share has a certain declared face value, commonly known as the par value of a share(Dell XPS M2010 battery). The par value is the de minimis (minimum) amount of money that a business may issue and sell shares for in many jurisdictions and it is the value represented as capital in the accounting of the business. In other jurisdictions, however, shares may not have an associated par value at all(Dell Inspiron Mini 12 battery). Such stock is often called non-par stock. Shares represent a fraction of ownership in a business. A business may declare different types (classes) of shares, each having distinctive ownership rules, privileges, or share values(SONY VGP-BPS9A/S battery).

Ownership of shares is documented by issuance of a stock certificate. A stock certificate is a legal document that specifies the amount of shares owned by the shareholder, and other specifics of the shares, such as the par value, if any, or the class of the shares(SONY VGP-BPS9/B battery).

Usage

Used in the plural, stocks is often used as a synonym for shares. Traditionalist demands for the plural stocks to be used only when referring to stocks of more than one company are rarely heard nowadays(SONY VGP-BPS9/S battery).

In the United Kingdom, Republic of Ireland, South Africa, and Australia, stock can also refer to completely different financial instruments such as government bonds or, less commonly, to all kinds of marketable securities(SONY VGP-BPS9A battery).

Types of stock

Stock typically takes the form of shares of either common stock or preferred stock. As a unit of ownership, common stock typically carries voting rights that can be exercised in corporate decisions(SONY VGP-BPS9A/B battery). Preferred stock differs from common stock in that it typically does not carry voting rights but is legally entitled to receive a certain level of dividend payments before any dividends can be issued to other shareholders. Convertible preferred stock is preferred stock that includes an option for the holder to convert the preferred shares into a fixed number of common shares(HP Pavilion DV6-1210SA battery), usually anytime after a predetermined date. Shares of such stock are called "convertible preferred shares" (or "convertible preference shares" in the UK)

New equity issues may have specific legal clauses attached that differentiate them from previous issues of the issuer. Some shares of common stock may be issued without the typical voting rights, for instance(SONY VGP-BPS11 battery), or some shares may have special rights unique to them and issued only to certain parties. Often, new issues that have not been registered with a securities governing body may be restricted from resale for certain periods of time.

Preferred stock may be hybrid by having the qualities of bonds of fixed returns and common stock voting rights. They also have preference in the payment of dividends over common stock and also have been given preference at the time of liquidation over common stock. They have other features of accumulation in dividend(SONY VGP-BPL11 battery).

Stock derivatives

A stock derivative is any financial instrument which has a value that is dependent on the price of the underlying stock. Futures and options are the main types of derivatives on stocks. The underlying security may be a stock index or an individual firm's stock, e.g. single-stock futures(SONY VGP-BPL12 battery).

Stock futures are contracts where the buyer is long, i.e., takes on the obligation to buy on the contract maturity date, and the seller is short, i.e., takes on the obligation to sell. Stock index futures are generally not delivered in the usual manner, but by cash settlement(SONY VGP-BPS12 battery).

A stock option is a class of option. Specifically, a call option is the right (not obligation) to buy stock in the future at a fixed price and a put optionis the right (not obligation) to sell stock in the future at a fixed price. Thus, the value of a stock option changes in reaction to the underlying stock of which it is a derivative(SONY VGP-BPS14 Battery). The most popular method of valuing stock options is the Black Scholes model. Apart from call options granted to employees, most stock options are transferable.

History

During Roman times, the empire contracted out many of its services to private groups called publicani(SONY VGP-BPS14/B Battery). Shares in publicani were called "socii" (for large cooperatives) and "particulae" which were analogous to today's Over-The-Counter shares of small companies. Though the records available for this time are incomplete, Edward Chancellor states in his book Devil Take the Hindmost that there is some evidence that a speculation in these shares became increasingly widespread and that perhaps the first everspeculative bubble in "stocks" occurred(SONY VGP-BPS14/S Battery).

The first company to issue shares of stock after the Middle Ages was the Dutch East India Company in 1606. The innovation of joint ownership made a great deal ofEurope's economic growth possible following the Middle Ages. The technique of pooling capital to finance the building of ships(SONY VGP-BPS14B Battery), for example, made the Netherlands amaritime superpower. Before adoption of the joint-stock corporation, an expensive venture such as the building of a merchant ship could be undertaken only by governments or by very wealthy individuals or families(SONY VGP-BPS22 battery).

Economic historians find the Dutch stock market of the 17th century particularly interesting: there is clear documentation of the use of stock futures, stock options, short selling, the use of credit to purchase shares, a speculative bubble that crashed in 1695, and a change in fashion that unfolded and reverted in time with the market(SONY VGP-BPS18 battery) (in this case it was headdresses instead of hemlines). Dr. Edward Stringham also noted that the uses of practices such as short selling continued to occur during this time despite the government passing laws against it. This is unusual because it shows individual parties fulfilling contracts that were not legally enforceable and where the parties involved could incur a loss(SONY VGP-BPS22/A battery). Stringham argues that this shows that contracts can be created and enforced without state sanction or, in this case, in spite of laws to the contrary.

Shareholder

A shareholder (or stockholder) is an individual or company (including a corporation) that legally owns one or more shares of stock in a joint stock company. Both private and public traded companies have shareholders. Companies listed at the stock market are expected to strive to enhance shareholder value(SONY VGP-BPS22A battery).

Shareholders are granted special privileges depending on the class of stock, including the right to vote on matters such as elections to the board of directors, the right to share in distributions of the company's income, the right to purchase new shares issued by the company(SONY VGP-BPL10 battery), and the right to a company's assets during aliquidation of the company. However, shareholder's rights to a company's assets are subordinate to the rights of the company's creditors.

Shareholders are considered by some to be a partial subset of stakeholders, which may include anyone who has a direct or indirect equity interest in the business entity or someone with even a non-pecuniary interest in a non-profit organization. Thus it might be common to call volunteer contributors to an associationstakeholders, even though they are not shareholders(SONY VGP-BPS10 battery).

Although directors and officers of a company are bound by fiduciary duties to act in the best interest of the shareholders, the shareholders themselves normally do not have such duties towards each other(Dell Latitude E6500 battery).

However, in a few unusual cases, some courts have been willing to imply such a duty between shareholders. For example, in California, USA, majority shareholders of closely held corporations have a duty to not destroy the value of the shares held by minority shareholders(Dell Latitude E6400 battery).

The largest shareholders (in terms of percentages of companies owned) are often mutual funds, and, especially, passively managed exchange-traded funds.

Application

The owners of a company may want additional capital to invest in new projects within the company. They may also simply wish to reduce their holding, freeing up capital for their own private use(Dell Latitude E5400 battery).

By selling shares they can sell part or all of the company to many part-owners. The purchase of one share entitles the owner of that share to literally share in the ownership of the company, a fraction of the decision-making power, and potentially a fraction of the profits, which the company may issue as dividends(SONY Vaio VGN-FW31J Battery).

In the common case of a publicly traded corporation, where there may be thousands of shareholders, it is impractical to have all of them making the daily decisions required to run a company. Thus, the shareholders will use their shares as votes in the election of members of the board of directors of the company(SONY Vaio VGN-FW32J Battery).

In a typical case, each share constitutes one vote. Corporations may, however, issue different classes of shares, which may have different voting rights. Owning the majority of the shares allows other shareholders to be out-voted - effective control rests with the majority shareholder (or shareholders acting in concert) (SONY Vaio VGN-FW17W Battery). In this way the original owners of the company often still have control of the company.

Shareholder rights

Although ownership of 50% of shares does result in 50% ownership of a company, it does not give the shareholder the right to use a company's building, equipment, materials, or other property. This is because the company is considered a legal person, thus it owns all its assets itself. This is important in areas such as insurance, which must be in the name of the company and not the main shareholder(SONY Vaio VGN-FW31E Battery).

In most countries, boards of directors and company managers have a fiduciary responsibility to run the company in the interests of its stockholders. Nonetheless, as Martin Whitman writes:

...it can safely be stated that there does not exist any publicly traded company where management works exclusively in the best interests of OPMI (SONY Vaio VGN-FW139E Battery) [Outside Passive Minority Investor] stockholders. Instead, there are both "communities of interest" and "conflicts of interest" between stockholders (principal) and management (agent). This conflict is referred to as the principal/agent problem. It would be naive to think that any management would forgo management compensation(SONY Vaio VGN-FW139E/H Battery), and management entrenchment, just because some of these management privileges might be perceived as giving rise to a conflict of interest with OPMIs.

Even though the board of directors runs the company, the shareholder has some impact on the company's policy, as the shareholders elect the board of directors. Each shareholder typically has a percentage of votes equal to the percentage of shares he or she owns(SONY Vaio VGN-FW465J Battery). So as long as the shareholders agree that the management (agent) are performing poorly they can elect a new board of directors which can then hire a new management team. In practice, however, genuinely contested board elections are rare. Board candidates are usually nominated by insiders or by the board of the directors themselves(SONY Vaio VGN-FW31M Battery), and a considerable amount of stock is held or voted by insiders.

Owning shares does not mean responsibility for liabilities. If a company goes broke and has to default on loans, the shareholders are not liable in any way. However, all money obtained by converting assets into cash will be used to repay loans and other debts first, so that shareholders cannot receive any money unless and until creditors have been paid (often the shareholders end up with nothing) (SONY VAIO VGN-FZ21E Battery).

Means of financing

Financing a company through the sale of stock in a company is known as equity financing. Alternatively, debt financing (for example issuing bonds) can be done to avoid giving up shares of ownership of the company. Unofficial financing known as trade financing usually provides the major part of a company's working capital (day-to-day operational needs) (SONY VAIO VGN-FZ21Z Battery).

Trading

The shares of a company may in general be transferred from shareholders to other parties by sale or other mechanisms, unless prohibited. Most jurisdictions have established laws and regulations governing such transfers, particularly if the issuer is a publicly-traded entity.

The desire of stockholders to trade their shares has led to the establishment of stock exchanges(SONY VAIO VGN-FZ21J Battery). A stock exchange is an organization that provides a marketplace for trading shares and other derivatives and financial products. Today, investors are usually represented by a stock broker who buys and sells shares of a wide range of companies on the exchanges(SONY Vaio VGN-FW11 Battery). A company may list its shares on an exchange by meeting and maintaining the listing requirements of a particular stock exchange. In the United States, through the inter-market quotation system, stocks listed on one exchange can also be traded on other participating exchanges, including the Electronic Communication Networks (ECNs), such as Archipelago or Instinet(SONY Vaio VGN-FW11M Battery).

Many large non-U.S companies choose to list on a U.S. exchange as well as an exchange in their home country in order to broaden their investor base. These companies must maintain a block of shares at a bank in the US, typically a certain percentage of their capital(SONY Vaio VGN-FW11S Battery). On this basis, the holding bank establishes American Depositary Shares and issues an American Depository Receipt (ADR) for each share a trader acquires. Likewise, many large U.S. companies list their shares at foreign exchanges to raise capital abroad(SONY Vaio VGN-FW21E Battery).

Small companies that do not qualify and cannot meet the listing requirements of the major exchanges may be traded over the counter (OTC) by an off-exchange mechanism in which trading occurs directly between parties. The major OTC markets in the United States are the electronic quotation systems OTC Bulletin Board (OTCBB) (SONY Vaio VGN-FW21J Battery) and the Pink OTC Markets (Pink Sheets) where individual retail investors are also represented by a brokerage firm and the quotation service's requirements for a company to be listed are minimal. Shares of companies in bankruptcy proceeding are usually listed by these quotation services after the stock is delisted from an exchange(SONY Vaio VGN-FW21L Battery).

Buying

There are various methods of buying and financing stocks. The most common means is through a stock broker. Whether they are a full serviceor discount broker, they arrange the transfer of stock from a seller to a buyer. Most trades are actually done through brokers listed with a stock exchange(SONY Vaio VGN-FW21M Battery).

There are many different stock brokers from which to choose, such as full service brokers or discount brokers. The full service brokers usually charge more per trade, but give investment advice or more personal service; the discount brokers offer little or no investment advice but charge less for trades(SONY VGP-BPS13Q Battery). Another type of broker would be a bank or credit union that may have a deal set up with either a full service or discount broker.

There are other ways of buying stock besides through a broker. One way is directly from the company itself. If at least one share is owned, most companies will allow the purchase of shares directly from the company through their investor relations departments(SONY VGP-BPS13B/Q Battery). However, the initial share of stock in the company will have to be obtained through a regular stock broker. Another way to buy stock in companies is through Direct Public Offerings which are usually sold by the company itself. A direct public offering is an initial public offering in which the stock is purchased directly from the company, usually without the aid of brokers(SONY VGN NR11S/S battery).

When it comes to financing a purchase of stocks there are two ways: purchasing stock with money that is currently in the buyer's ownership, or by buying stock on margin. Buying stock on margin means buying stock with money borrowed against the stocks in the same accoun(SONY VGN NR11M/S battery)t. These stocks, or collateral, guarantee that the buyer can repay the loan; otherwise, the stockbroker has the right to sell the stock (collateral) to repay the borrowed money. He can sell if the share price drops below the margin requirement, at least 50% of the value of the stocks in the account. Buying on margin works the same way as borrowing money to buy a car or a house, using a car or house as collateral(SONY VGN NR11Z/S battery). Moreover, borrowing is not free; the broker usually charges 8-10% interest.

Selling

Selling stock is procedurally similar to buying stock. Generally, the investor wants to buy low and sell high, if not in that order (short selling); although a number of reasons may induce an investor to sell at a loss, e.g., to avoid further loss(SONY VGN NR11Z/T battery).

As with buying a stock, there is a transaction fee for the broker's efforts in arranging the transfer of stock from a seller to a buyer. This fee can be high or low depending on which type of brokerage, full service or discount, handles the transaction(SONY VGP-BPS13A/Q Battery).

After the transaction has been made, the seller is then entitled to all of the money. An important part of selling is keeping track of the earnings. Importantly, on selling the stock, in jurisdictions that have them,capital gains taxes will have to be paid on the additional proceeds, if any, that are in excess of the cost basis(SONY Vaio PCG-F305 battery).

Stock price fluctuations

The price of a stock fluctuates fundamentally due to the theory of supply and demand. Like all commodities in the market, the price of a stock is sensitive to demand. However, there are many factors that influence the demand for a particular stock(SONY VGP-BPS21/S Battery). The field of fundamental analysisand technical analysis attempt to understand market conditions that lead to price changes, or even predict future price levels. A recent study shows that customer satisfaction, as measured by the American Customer Satisfaction Index (ACSI), (SONY VGP-BPS21 Battery) is significantly correlated to the market value of a stock. Stock price may be influenced by analyst's business forecast for the company and outlooks for the company's general market segment.

Share price determination

At any given moment, an equity's price is strictly a result of supply and demand. The supply is the number of shares offered for sale at any one moment(SONY VGP-BPS21B Battery). The demand is the number of shares investors wish to buy at exactly that same time. The price of the stock moves in order to achieve and maintain equilibrium.

When prospective buyers outnumber sellers, the price rises(SONY VGP-BPS21A/B Battery). Eventually, sellers attracted to the high selling price enter the market and/or buyers leave, achieving equilibrium between buyers and sellers. When sellers outnumber buyers, the price falls. Eventually buyers enter and/or sellers leave, again achieving equilibrium.

Thus, the value of a share of a company at any given moment is determined by all investors voting with their money. If more investors want a stock and are willing to pay more, the price will go up. If more investors are selling a stock and there aren't enough buyers, the price will go down(SONY VAIO PCG-5K1L battery).

Note: "For Nasdaq-listed stocks, the price quote includes information on the bid and ask prices for the stock."

Of course, that does not explain how people decide the maximum price at which they are willing to buy or the minimum at which they are willing to sell. In professional investment circles the efficient market hypothesis (EMH) continues to be popular(SONY VAIO PCG-6W2L battery), although this theory is widely discredited in academic and professional circles. Briefly, EMH says that investing is overall (weighted by a Stdev) rational; that the price of a stock at any given moment represents a rational evaluation of the known information that might bear on the future value of the company(SONY VAIO PCG-7112L battery); and that share prices of equities are priced efficiently, which is to say that they represent accurately the expected value of the stock, as best it can be known at a given moment. In other words, prices are the result of discounting expected future cash flows.

The EMH model, if true, has at least two interesting consequences(SONY VAIO PCG-8Z1L battery). First, because financial risk is presumed to require at least a small premium on expected value, the return on equity can be expected to be slightly greater than that available from non-equity investments: if not, the same rational calculations would lead equity investors to shift to these safer non-equity investments that could be expected to give the same or better return at lower risk(SONY VAIO PCG-8Z2L battery). Second, because the price of a share at every given moment is an "efficient" reflection of expected value, then—relative to the curve of expected return—prices will tend to follow a random walk, determined by the emergence of information (randomly) over time(SONY VAIO PCG-8Y2L battery). Professional equity investors therefore immerse themselves in the flow of fundamental information, seeking to gain an advantage over their competitors (mainly other professional investors) by more intelligently interpreting the emerging flow of information (news).

The EMH model does not seem to give a complete description of the process of equity price determination(SONY VAIO PCG-8Y1L battery). For example, stock markets are more volatile than EMH would imply. In recent years it has come to be accepted that the share markets are not perfectly efficient, perhaps especially in emerging markets or other markets that are not dominated by well-informed professional investors(SONY VAIO PCG-7Z2L battery).

Another theory of share price determination comes from the field of Behavioral Finance. According to Behavioral Finance, humans often make irrational decisions—particularly, related to the buying and selling of securities—based upon fears and misperceptions of outcomes(SONY VAIO PCG-7Z1L battery). The irrational trading of securities can often create securities prices which vary from rational, fundamental price valuations. For instance, during the technology bubble of the late 1990s (which was followed by the dot-com bust of 2000-2002), technology companies were often bid beyond any rational fundamental value because of what is commonly known as the "greater fool theory". The "greater fool theory" holds that(SONY VAIO PCG-7133L battery), because the predominant method of realizing returns in equity is from the sale to another investor, one should select securities that they believe that someone else will value at a higher level at some point in the future, without regard to the basis for that other party's willingness to pay a higher price. Thus, even a rational investor may bank on others' irrationality(SONY VAIO PCG-7113L battery).

Arbitrage trading

When companies raise capital by offering stock on more than one exchange, the potential exists for discrepancies in the valuation of shares on different exchanges. A keen investor with access to information about such discrepancies may invest in expectation of their eventual convergence(SONY VAIO PCG-6W3L battery), known as arbitrage trading. Electronic trading has resulted in extensive price transparency (efficient market hypothesis) and these discrepancies, if they exist, are short-lived and quickly equilibrate(SONY VAIO PCG-7111L battery).

Remote control

A remote control is a component of an electronics device, most commonly a television set, used for operating the television device wirelessly from a short line-of-sight distance(AKKU Sony VGP-BPS13).

The remote control can be contracted to remote or controller. It is known by many other names as well, such as converter clicker, "The box" didge, flipper, the tuner, the changer, or the button. Commonly, remote controls are Consumer IR devices used to issue commands from a distance to televisions or other consumer electronics such as stereo systems(AKKU Sony VGP-BPS13A/B), DVD players and dimmers. Remote controls for these devices are usually small wireless handheld objects with an array of buttons for adjusting various settings such as television channel, track number, and volume. In fact, for the majority of modern devices with this kind of control(AKKU Sony VGP-BPS13B/B), the remote contains all the function controls while the controlled device itself only has a handful of essential primary controls. Most of these remotes communicate to their respective devices via infrared (IR) signals and a few via radio signals. Earlier remote controls in the 1970s used ultrasonic tones(AKKU Sony VGP-BPS13/S). Television IR signals can be mimicked by a universal remote, which is able to emulate the functionality of most major brand television remote controls. They are usually powered by small AAA or AA or sometimes A23 size batteries(AKKU Sony VGP-BPS13B/S).

History

One of the earliest examples of remote control was developed in 1898 by Nikola Tesla, and described in his patent, U.S. Patent 613,809, named Method of an Apparatus for Controlling Mechanism of Moving Vehicle or Vehicles. In 1898, he demonstrated a radio-controlled boat to the public during an electrical exhibition at Madison Square Garden. Tesla called his boat a "teleautomaton"(AKKU Sony VGP-BPS13A/S).

In 1903, Leonardo Torres Quevedo presented the Telekino at the Paris Academy of Science, accompanied by a brief, and making an experimental demonstration. In the same time he obtained a patent in France, Spain, Great Britain, and the United States(AKKU Sony VGP-BPS13A/Q). The Telekino consisted of a robot that executed commands transmitted by electromagnetic waves. It constituted the world's first apparatus for radio controland was a pioneer in the field of remote control. In 1906, in the presence of the king and before a great crowd, Torres successfully demonstrated the invention in the port of Bilbao(AKKU Sony VGP-BPS13B/Q), guiding a boat from the shore. Later, he would try to apply the Telekino to projectiles and torpedoes, but had to abandon the project for lack of financing.

The first remote-controlled model aeroplane flew in 1932, and the use of remote control technology for military purposes was worked intensively during the Second World War, one result of this being the German Wasserfall missile(AKKU Sony VGP-BPS13Q).

By the late 1930s, several radio manufacturers offered remote controls for some of their higher-end models. Most of these were connected to the set being controlled by wires, but the Philco Mystery Control (1939) was a battery-operated low-frequency radio transmitter, thus making it the first wireless remote control for a consumer electronics device(Sony VGP-BPL8 Battery).

Television remote controls

The first remote intended to control a television was developed by Zenith Radio Corporation in 1950. The remote, called "Lazy Bones", was connected to the television set by a wire. A wireless remote control, the "Flashmatic", was developed in 1955; it worked by shining a beam of light onto a photoelectric cell(Sony VGP-BPL8A Battery), but the cell did not distinguish between light from the remote and light from other sources. The Flashmatic also had to be pointed very precisely at the receiver in order to work.

The Zenith Space Commander Six hundred remote control

In 1956, Robert Adler developed "Zenith Space Command", a wireless remote. It was mechanical and used ultrasound to change the channel and volume(Sony VGN-FZ130E/B Battery). When the user pushed a button on the remote control, it clicked and struck a bar, hence the term "clicker". Each bar emitted a different frequency and circuits in the television detected this sound. The invention of the transistor made possible cheaper electronic remotes that contained a piezoelectric crystal (Sony VGN-FZ130E/BA Battery)that was fed by an oscillating electric current at a frequency near or above the upper threshold of human hearing, though still audible to dogs. The receiver contained a microphone attached to a circuit that was tuned to the same frequency. Some problems with this method were that the receiver could be triggered accidentally by naturally occurring noises(Sony VGN-FZ130E/BB Battery), and some people could hear the piercing ultrasonic signals. There was an incident in which a toy xylophone changed the channels on such sets because some of the overtones from the xylophone matched the remote's ultrasonic frequency.

The impetus for a more complex type of television remote control came in the late 1970s, with the development of the Ceefax teletext service by the BBC(Sony VGP-BPL9 Akku). Most commercial remote controls at that time had a limited number of functions, sometimes as few as three: next channel, previous channel, and volume/off. This type of control did not meet the needs of teletext sets, where pages were identified with three-digit numbers(Sony VGP-BPL9/B Akku). A remote control to select teletext pages would need buttons for each numeral from zero to nine, as well as other control functions, such as switching from text to picture, and the normal television controls of volume, channel, brightness, colour intensity, etc. Early teletext sets used wired remote controls to select pages(Sony VGP-BPL9/S Akku), but the continuous use of the remote control required for teletext quickly indicated the need for a wireless device. So BBC engineers began talks with one or two television manufacturers, which led to early prototypes in around 1977–1978 that could control many more functions(Sony VGP-BPL9A/B Akku). ITT was one of the companies and later gave its name to the ITT protocol of infrared communication.

In 1980, a Canadian company, Viewstar, Inc., was formed by engineer Paul Hrivnak and started producing a cable TV converter with an infrared remote control. The product was sold through Philips for approximately $190 CAD(Sony VGP-BPL9A Akku). At the time the most popular remote control was the Starcom of Jerrold (a division of General Instruments) which used 40-kHz sound to change channels. The Viewstar converter was an immediate success, the millionth converter being sold on March 21, 1985, with 1.6 million sold by 1989(Sony VGP-BPL9 Akku).

Effect of the early television remote control

The remote allowed audiences, for the first time, to interact with their TV without touching it. They no longer watched programs just because they did not want to get up to change the channel. They could also channel surf during commercials, or turn the sound off(Sony VGP-BPS21 Akku).

The invention of the remote control has led to several changes in television programming. One was the creation of split screen credits. According to James Gleick, an NBC research team discovered that when the credits started rolling after a program, 25% of its viewers would change the channel before it was over(Sony VGP-BPS21A Akku). Because of this, the NBC 2000 unit invented the “squeeze and tease” which squeezed the credits onto one third of the screen while the final minutes of the broadcast aired simultaneously.

The remote control also led to an adjustment in commercial airings. Networks began to feel that they could not afford to have commercials between programs because it would detract viewers from staying tuned in to their channel(Sony VGP-BPS21B Akku). Programmers decided to place commercials in the middle of programs to make the transition to the next show direct.

With networks keeping in mind that people were equipped with remotes, 30-second advertisement spots were cut into segments of eight seconds or less. MTV was made up of this high-speed and broken cutting style(Sony VGP-BPS21A/B Akku), which aired music videos that were around three-minutes and each shot no more than two or three seconds. But MTV felt that even these three-minute segments were too long, so they created an animated series called Beavis and Butthead, to keep their viewer’s attention(Sony VGP-BPS21/S Akku). In the show, they would show segments of music videos and then switch back to the characters and offer dialogue and action while the music video played in the background. Beavis and Butthead was purposefully stagnant, with slow dialogue, dependence on reaction shots, and emphasis on animation and pacing(Akku Sony VGP-BPL14), with the last fraction of a second of sound track is overlaid with the first fraction of a second of the visual track for the next scene.

Other remote controls

In the 1980s Steve Wozniak of Apple, started a company named CL 9. The purpose of this company was to create a remote control that could operate multiple electronic devices( Akku Sony VGP-BPL14 ). The CORE unit (Controller Of Remote Equipment) was introduced in the fall of 1987. The advantage to this remote controller was that it could “learn” remote signals from different devices. It had the ability to perform specific or multiple functions at various times with its built-in clock. It was the first remote control that could be linked to a computer and loaded with updated software code as needed(Akku Sony VGP-BPS14/S ).

The CORE unit never made a huge impact on the market. It was much too cumbersome for the average user to program, but it received rave reviews from those who could. These obstacles eventually led to the demise of CL 9, but two of its employees continued the business under the name Celadon. This was one of the first computer-controlled learning remote controls on the market(Akku Sony VGP-BPL14/B).

The proliferation of remote controls

By the early 2000s, the number of consumer electronic devices in most homes greatly increased, along with the number of remotes to control those devices. According to the Consumer Electronics Association, an average American home has four remotes. To operate a home theater as many as five or six remotes may be required(Akku Sony VGP-BPS14/B ), including one for cable or satellite receiver, VCR or digital video recorder (DVR/PVR), DVD player, TV and audio amplifier. Several of these remotes may need to be used sequentially but, as there are no accepted interface guidelines, the process is increasingly cumbersome(AKKU sony VAIO VGN-FW21E).

Many specialists, including Jakob Nielsen, a renowned usability specialist and Robert Adler, the inventor of the modern remote, note how confusing, unwieldy and frustrating the multiplying remotes have become. Because of this proliferation of remote controls, universal remote controls that manage multiple devices are becoming increasingly popular(AKKU Sony VAIO VGN-FW21I).

Remote control applications on mobile devices

In the late 2000s-early 2010s, a number of smartphone and portable media player platforms were provided with installable software applications which allow for the remote controlling of media centers and media players on home theater PCs and general-purpose personal computers over wi-Fi, such as iTunes Remote on iPhone OS(AKKU Sony VAIO VGN-FW21L). In comparison to the user interfaces of physically buttoned dedicated remote control devices, the user interfaces of these remote control applications are designed to take advantage of the dynamic graphics offered by usually touchscreened handheld devices, making for larger virtual buttons and virtual keyboards(AKKU Sony VAIO VGN-FW21Z).

Most developers of remote control applications for handhelds usually architect the software for usage with specific media player or media center applications (i.e., iTunes Remote for iTunes and iTunes-based software from Apple, Boxee remote for Boxee, DVR Remote for TiVo, VLC Remote for VLC, etc.) (AKKU Sony VAIO VGN-FW21M).

TechniqueThe opto components, circuits and mathematics

The emission spectrum of a typical sound system remote control is in the near infrared.

The infrared diode modulates at a speed corresponding to a particular function. When seen through a digital camera, the diode appears to illuminate purple light(AKKU Sony VAIO VGN-FW31M).

Most remote controls for electronic appliances use a near infrared diode to emit a beam of light that reaches the device. A 940 nm wavelength LED is typical. This infrared light is invisible to the human eye, but picked up by sensors on the receiving device. Video cameras see the diode as if it produces visible purple light(AKKU Sony VAIO VGN-FW31J).

With a single channel (single-function, one-button) remote control the presence of a carrier signal can be used to trigger a function. For multi-channel (normal multi-function) remote controls more sophisticated procedures are necessary: one consists of modulating the carrier with signals of different frequency(AKKU Sony VAIO VGN-FW31E). After the demodulation of the received signal, the appropriate frequency filters are applied to separate the respective signals. Nowadays digital procedures are more commonly used. One can often hear the signals being modulated on the infrared carrier by operating a remote control in very close proximity to an AM radio not tuned to a station(AKKU Sony VAIO VGN-FW31Z).

Consumer electronics infrared protocols

Different manufacturers of infrared remote controls use different protocols to transmit the infrared commands. The RC-5 protocol that has its origins within Philips, uses, for instance, a total of 14 bits for each button press(AKKU Sony VAIO VGN-FW31ZJ). The bit pattern is modulated onto a carrier frequency that, again, can be different for different manufacturers and standards, in the case of RC-5, a 36 kHz carrier is being used. Other consumer infrared protocols are, for instance, the different SIRCS versions used by Sony, the RC-6 from Philips, the Ruwido R-Step, or the NEC TC101 protocol(AKKU Sony VAIO VGN-FW32Z).

Infrared, line of sight and operating angle

Since infrared (IR) remote controls use light, they require line of sight to operate the destination device. The signal can, however, be reflected by mirrors, just like any other light source(AKKU Sony VAIO PCG-5G2L).

If operation is required where no line of sight is possible, for instance when controlling equipment in another room or installed in a cabinet, many brands of IR extenders are available for this on the market. Most of these have an IR receiver, picking up the IR signal and relaying it via radio waves to the remote part, which has an IR transmitter mimicking the original IR control(AKKU Sony VAIO PCG-5G3L ).

Infrared receivers also tend to have a more or less limited operating angle, which mainly depends on the optical characteristics of the phototransistor. However, it’s easy to increase the operating angle using a matte transparent object in front of the receiver. A description can be found here(Sony VAIO PCG-5J1L Akku).

Radio Remote Control Systems

this is a typical photo of both outer case and inner circuit of garage door opener remote control.

Radio remote control (RF Remote Control) is a way to control distance objects using a variety of radio signals transmitted by the remote control device. By using radio remote control system, you can control a variety of mechanical or electronic devices to complete various operations(Sony VAIO PCG-5J2L Akku), such as closing circuit, move handle, start motor, etc. As a complementary method to infrared remote control type, the radio remote control is widely used in garage door remote control, electric gate remote control, automatic barrier remote control, burglar alarm, industrial remote control and wireless home alarm systems(Sony VAIO PCG-5K2L Akku).

A radio remote control system commonly has two parts: transmit and receive.

Transmitter part is generally divided into two types, namely, rf remote control and transmitter module, by the way of using, the rf remote control can be used independently as a whole while the transmitter module is used as a component in the circuit(Sony VAIO PCG-5K1L Akku), the advantage of using transmitter model is it can be seamlessly connected with application circuit, and it's size is small, but users must have a knowledge of circuit to use the transmitter module, the rf remote control is much more easy to use at this point(Sony VAIO PCG-6S1L Akku).

Receiver part also is generally divided into two types, namely, the super-regenerative receiver and the superheterodyne receiver, super-regenerative receiver is actually working like the regeneration of under intermittent oscillation detection circuit(Sony VAIO PCG-6S2L Akku). While Superheterodyne type is working like the one in radio receiver. Superheterodyne receiver features stability, high sensitivity and the anti-interference ability is relatively good, while super-regenerative receiver features a small package and the price is also cheaper(Sony VAIO PCG-6W1L Akku).

Fixed-code RF Remote Control DIP Switch Calculator

this is a dip switch calculator designed for addressing fixed code garage door opener remote controls.

Tri-state DIP switches are widely used in fixed-code RF Remote Controls to define the code of address pins, while in many circumstances, it's usually useful to calculate the dip switch settings, a calculator like the following will save you a lot of time(Sony VAIO PCG-6W2L Akku).

The RF Remote Control Tri-State DIP Switch Calculator is capable of calculating DIP switches up to 8 positions, and will convert any number from 0 to 38-1 to ternary and then display it in a visual form. Our RF Remote Control Tri-State DIP Switch Calculator will assist you working out ternary values in addressing various fixed-code RF Remote Controls(Sony VAIO PCG-6W3L Akku), thus making the DIP switch settings for RF Remote Control addressing more efficiently.

Usage

Industry

Remote control is used for controlling substations, pump storage power stations and HVDC-plants. For these systems often PLC-systems working in the longwave range are used(Sony VAIO PCG-7111L Akku).

Military

Only in the military field of use of remote controls can you find the jammers and the countermeasures against the jammers.

Jammers are used to disable or sabotage the enemy's use of remote controls. IED jamming systems, Radio jamming, Electronic warfare(Sony VAIO PCG-7112L Akku)

The distances for military remote controls also tend to be much longer, up to intercontinental distance satellite linked remote controls used by the U.S. for their unmanned airplanes (drones) in Afghanistan, Iraq and Pakistan.

Remote controls are used by insurgents in Iraq and Afghanistan to attack coalition and government troops with roadside IEDs (Improvised explosive device, Explosively formed penetrator) (Sony VAIO PCG-7113L Akku).

The arms race and the fact that the enemy is many times closer to the receiver has made it more complicated and too expensive to build radio remote controls for roadside bombs that are immune to jammers. The simplest types of radio remote controls have been almost entirely disabled by the advanced jammers(Sony VAIO PCG-7131L Akku), but are still in use against unprotected Iraqi and Afghan national troops and civilian targets. One of the simplest solutions against the radio jammers is to fool the jammer itself to ignite the bomb(Sony VAIO PCG-7132L Akku).

Optical types of remote controls that uses light instead of radio are still immune to the jammers. The resistance in Iraq is reported in the media to use modified TV remote controls to detonate the bombs.

Military history

In World War I, the Imperial German Navy employed FL-boats (Fernlenkboote) against coastal shipping(Sony VAIO PCG-7133L Akku). These were driven by internal combustion engines, and controlled remotely from a shore station through several miles of wire wound on a spool on the boat. An aircraft was used to signal directions to the shore station. EMBs carried a high explosive charge in the bow and traveled at speeds of thirty knots(Sony VAIO PCG-7z1L Akku).

The Soviet Red Army used remotely controlled teletanks during 1930s in the Winter War against Finland and the early stages of World War II. A teletank is controlled by radio from a control tank at a distance of 500–1,500 meters, the two constituting a telemechanical group(Sony VAIO PCG-7z1L Akku). The Red Army fielded at least two teletank battalions at the beginning of the Great Patriotic War. There were also remotely controlled cutters and experimental remotely controlled planes in the Red Army(Sony VAIO PCG-8Y1L Akku).

Space

Remote control technology is also used in space travel, for instance the Russian Lunokhod vehicles were remote-controlled from the ground. Direct remote control of space vehicles at greater distances from the earth is not practical due to increasing signal delay times(Sony VAIO PCG-8Y2L Akku).

Video games

Video game consoles had not used wireless controllers until recently, mainly because of the difficulty involved in playing the game while keeping the infrared transmitter pointed at the console. Early wireless controllers were cumbersome and when powered on alkaline batteries, lasted only a few hours before they needed replacement(Sony VAIO PCG-8Z1L Akku). Some wireless controllers were produced by third parties, in most cases using a radio link instead of infrared. Even these were very inconsistent, and in some cases, had transmission delays, making them virtually useless. The first official wireless controller made by a first party manufacturer was the WaveBird for Nintendo Gamecube(Sony VAIO PCG-8Z2L Akku). The Wavebird changed the face of wireless technology in video game consoles. In the current generation of gaming consoles, wireless controllers have become the standard.

PC control

Existing infrared remote controls can be used to control PC applications. Any application that supports shortcut keys can be controlled via IR remote controls from other home devices (TV, VCR, AC, ...) (Akku Sony VGN-NR11M/S). This is widely used with multimedia applications for PC based Home Theatre systems. For this to work, you need a device that decodes IR remote control data signals and a PC application that communicates to this device connected to PC. Connection can be made via serial port, USB port or motherboard IrDA connector(Akku Sony VGN-NR11S/S). Such devices are commercially available or it can be home made using low cost microcontrollers.

LIRC(Linux IR Remote control) and Win-LIRC (for Windows) software are developed for the purpose of controlling PC using TV remote and can be also used for homebrew remote with lesser modification. They support almost all TV remotes(Akku Sony VGN-NR11Z/S). Examples of many PC remote control ckts are available here

Standby power

To be turned on by a wireless remote, the controlled appliance must always be partly on, consuming standby power.

Alternatives

Hand-gesture recognition is an alternative to remote controls for television sets(Akku Sony VGN-NR11Z/T).