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70-416: Hydrogen sulfide is toxic to humans and most other animals by inhibiting cellular respiration in a manner similar to hydrogen cyanide . When it is inhaled or its salts are ingested in high amounts, damage to organs occurs rapidly with symptoms ranging from breathing difficulties to convulsions and death. Despite this, the human body produces small amounts of this sulfide and its mineral salts, and uses it as

140-523: A reducing agent , as indicated by its ability to reduce sulfur dioxide in the Claus process . Hydrogen sulfide burns in oxygen with a blue flame to form sulfur dioxide ( SO 2 ) and water : If an excess of oxygen is present, sulfur trioxide ( SO 3 ) is formed, which quickly hydrates to sulfuric acid : It is slightly soluble in water and acts as a weak acid ( p K a  = 6.9 in 0.01–0.1 mol/litre solutions at 18 °C), giving

210-513: A signalling molecule . Hydrogen sulfide is often produced from the microbial breakdown of organic matter in the absence of oxygen, such as in swamps and sewers; this process is commonly known as anaerobic digestion , which is done by sulfate-reducing microorganisms . It also occurs in volcanic gases , natural gas deposits, and sometimes in well-drawn water. Hydrogen sulfide is slightly denser than air. A mixture of H 2 S and air can be explosive. In general, hydrogen sulfide acts as

280-458: A cell releases chemical energy to fuel cellular activity. The overall reaction occurs in a series of biochemical steps, some of which are redox reactions. Although cellular respiration is technically a combustion reaction , it is an unusual one because of the slow, controlled release of energy from the series of reactions. Nutrients that are commonly used by animal and plant cells in respiration include sugar , amino acids and fatty acids , and

350-471: A few weeks. Long-term, low-level exposure may result in fatigue , loss of appetite, headaches , irritability, poor memory, and dizziness . Chronic exposure to low level H 2 S (around 2 ppm ) has been implicated in increased miscarriage and reproductive health issues among Russian and Finnish wood pulp workers, but the reports have not (as of 1995) been replicated. Short-term, high-level exposure can induce immediate collapse, with loss of breathing and

420-850: A high probability of death. If death does not occur, high exposure to hydrogen sulfide can lead to cortical pseudolaminar necrosis , degeneration of the basal ganglia and cerebral edema . Although respiratory paralysis may be immediate, it can also be delayed up to 72 hours. Inhalation of H 2 S resulted in about 7 workplace deaths per year in the U.S. (2011–2017 data), second only to carbon monoxide (17 deaths per year) for workplace chemical inhalation deaths. Treatment involves immediate inhalation of amyl nitrite , injections of sodium nitrite , or administration of 4-dimethylaminophenol in combination with inhalation of pure oxygen, administration of bronchodilators to overcome eventual bronchospasm , and in some cases hyperbaric oxygen therapy (HBOT). HBOT has clinical and anecdotal support. Hydrogen sulfide

490-488: A membrane. This potential is then used to drive ATP synthase and produce ATP from ADP and a phosphate group. Biology textbooks often state that 38 ATP molecules can be made per oxidized glucose molecule during cellular respiration (2 from glycolysis, 2 from the Krebs cycle , and about 34 from the electron transport system). However, this maximum yield is never quite reached because of losses due to leaky membranes as well as

560-446: A presence of a catalyst under atmospheric pressure around 1200 °C into hydrogen and sulfur. Hydrogen sulfide reacts with metal ions to form metal sulfides, which are insoluble, often dark colored solids. Lead(II) acetate paper is used to detect hydrogen sulfide because it readily converts to lead(II) sulfide , which is black. Treating metal sulfides with strong acid or electrolysis often liberates hydrogen sulfide. Hydrogen sulfide

630-441: A result of the action of sulfate-reducing bacteria . Hydrogen sulfide is produced by the human body in small quantities through bacterial breakdown in the intestinal tract of proteins containing sulfur; it therefore contributes to the characteristic odor of flatulence. It is also produced in the mouth ( halitosis ). A portion of global H 2 S emissions are due to human activity. By far the largest industrial source of H 2 S

700-458: A reversible reaction. Lactate can also be used as an indirect precursor for liver glycogen. During recovery, when oxygen becomes available, NAD attaches to hydrogen from lactate to form ATP. In yeast, the waste products are ethanol and carbon dioxide . This type of fermentation is known as alcoholic or ethanol fermentation . The ATP generated in this process is made by substrate-level phosphorylation , which does not require oxygen. Fermentation

770-611: A sour gas is any gas that specifically contains hydrogen sulfide in significant amounts, whereas an acid gas is any gas that contains significant amounts of acidic gases such as carbon dioxide (CO 2 ) or hydrogen sulfide. Thus, carbon dioxide by itself is an acid gas, not a sour gas. In addition to being toxic , hydrogen sulfide in the presence of water also damages piping and other equipment handling sour gas by sulfide stress cracking . Natural gas typically contains several ppm of volatile sulfur compounds, but gas from one well in Canada

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840-460: A waste product. Water heaters can aid the conversion of sulfate in water to hydrogen sulfide gas. This is due to providing a warm environment sustainable for sulfur bacteria and maintaining the reaction which interacts between sulfate in the water and the water heater anode, which is usually made from magnesium metal. H 2 S in the body acts as a gaseous signaling molecule with implications for health and in diseases. Hydrogen sulfide

910-643: Is petroleum refineries : The hydrodesulfurization process liberates sulfur from petroleum by the action of hydrogen. The resulting H 2 S is converted to elemental sulfur by partial combustion via the Claus process , which is a major source of elemental sulfur. Other anthropogenic sources of hydrogen sulfide include coke ovens, paper mills (using the Kraft process), tanneries and sewerage . H 2 S arises from virtually anywhere where elemental sulfur comes in contact with organic material, especially at high temperatures. Depending on environmental conditions, it

980-482: Is stinkdamp . Hydrogen sulfide is a highly toxic and flammable gas ( flammable range : 4.3–46%). It can poison several systems in the body, although the nervous system is most affected. The toxicity of H 2 S is comparable with that of carbon monoxide . It binds with iron in the mitochondrial cytochrome enzymes , thus preventing cellular respiration . Its toxic properties were described in detail in 1843 by Justus von Liebig . Even before hydrogen sulfide

1050-400: Is a vital process that occurs in the cells of all living organisms . Respiration can be either aerobic, requiring oxygen, or anaerobic; some organisms can switch between aerobic and anaerobic respiration. The reactions involved in respiration are catabolic reactions , which break large molecules into smaller ones, producing large amounts of energy (ATP). Respiration is one of the key ways

1120-780: Is active in the inner membrane it short circuits the coupling between the electron transport chain and ATP synthesis . The potential energy from the proton gradient is not used to make ATP but generates heat. This is particularly important in brown fat thermogenesis of newborn and hibernating mammals. According to some newer sources, the ATP yield during aerobic respiration is not 36–38, but only about 30–32 ATP molecules / 1 molecule of glucose , because: So finally we have, per molecule of glucose Altogether this gives 4 + 3 (or 5) + 20 + 3 = 30 (or 32) ATP per molecule of glucose These figures may still require further tweaking as new structural details become available. The above value of 3 H / ATP for

1190-427: Is also known to increase the levels of glutathione, which acts to reduce or disrupt ROS levels in cells. The field of H 2 S biology has advanced from environmental toxicology to investigate the roles of endogenously produced H 2 S in physiological conditions and in various pathophysiological states. H 2 S has been implicated in cancer and Down syndrome and vascular disease. It inhibits Complex IV of

1260-416: Is also responsible for tarnishing on various metals including copper and silver ; the chemical responsible for black toning found on silver coins is silver sulfide ( Ag 2 S ), which is produced when the silver on the surface of the coin reacts with atmospheric hydrogen sulfide. Coins that have been subject to toning by hydrogen sulfide and other sulfur-containing compounds may have the toning add to

1330-417: Is harmless. Hence, low levels of hydrogen sulfide may be tolerated indefinitely. Exposure to lower concentrations can result in eye irritation, a sore throat and cough , nausea, shortness of breath, and fluid in the lungs . These effects are believed to be due to hydrogen sulfide combining with alkali present in moist surface tissues to form sodium sulfide , a caustic . These symptoms usually subside in

1400-406: Is involved in vasodilation in animals, as well as in increasing seed germination and stress responses in plants. Hydrogen sulfide signaling is moderated by reactive oxygen species (ROS) and reactive nitrogen species (RNS). H 2 S has been shown to interact with NO resulting in several different cellular effects, as well as the formation of another signal called nitrosothiol. Hydrogen sulfide

1470-442: Is known to contain 90% hydrogen sulfide and others may have H 2 S contents in the tens of percent range. Within oil refineries or natural gas processing plants, the removal of hydrogen sulfide and other organosulfur compounds is referred to as "sweetening". The sweetened product lacks the sour, foul odors of mercaptans and hydrogen sulfide. Before a raw natural gas containing hydrogen sulfide or carbon dioxide can be used,

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1540-520: Is less efficient at using the energy from glucose: only 2 ATP are produced per glucose, compared to the 38 ATP per glucose nominally produced by aerobic respiration. Glycolytic ATP, however, is produced more quickly. For prokaryotes to continue a rapid growth rate when they are shifted from an aerobic environment to an anaerobic environment, they must increase the rate of the glycolytic reactions. For multicellular organisms, during short bursts of strenuous activity, muscle cells use fermentation to supplement

1610-476: Is modified to become α-ketoglutarate (5 carbons), succinyl-CoA , succinate , fumarate , malate and, finally, oxaloacetate . The net gain from one cycle is 3 NADH and 1 FADH 2 as hydrogen (proton plus electron) carrying compounds and 1 high-energy GTP , which may subsequently be used to produce ATP. Thus, the total yield from 1 glucose molecule (2 pyruvate molecules) is 6 NADH, 2 FADH 2 , and 2 ATP. In eukaryotes, oxidative phosphorylation occurs in

1680-416: Is natural gas with a high content of H 2 S . It can also be produced by treating hydrogen with molten elemental sulfur at about 450 °C. Hydrocarbons can serve as a source of hydrogen in this process. The very favorable thermodynamics for the hydrogenation of sulfur implies that the dehydrogenation (or cracking ) of hydrogen sulfide would require very high temperatures. A standard lab preparation

1750-442: Is not transferred to the mitochondrion and finally oxidized to the carbon dioxide (CO 2 ), but reduced to ethanol or lactic acid in the cytoplasm . Without oxygen, pyruvate ( pyruvic acid ) is not metabolized by cellular respiration but undergoes a process of fermentation . The pyruvate is not transported into the mitochondrion but remains in the cytoplasm, where it is converted to waste products that may be removed from

1820-468: Is pressurized at higher temperatures, then cooled, the critical temperature reaches 203 K (−70 °C), the highest accepted superconducting critical temperature as of 2015. By substituting a small part of sulfur with phosphorus and using even higher pressures, it has been predicted that it may be possible to raise the critical temperature to above 0 °C (273 K) and achieve room-temperature superconductivity . Hydrogen sulfide decomposes without

1890-879: Is responsible for deterioration of material through the action of some sulfur oxidizing microorganisms. It is called biogenic sulfide corrosion . In 2011 it was reported that increased concentrations of H 2 S were observed in the Bakken formation crude, possibly due to oil field practices, and presented challenges such as "health and environmental risks, corrosion of wellbore, added expense with regard to materials handling and pipeline equipment, and additional refinement requirements". Besides living near gas and oil drilling operations, ordinary citizens can be exposed to hydrogen sulfide by being near waste water treatment facilities, landfills and farms with manure storage. Exposure occurs through breathing contaminated air or drinking contaminated water. In municipal waste landfill sites ,

1960-447: Is the preferred method of pyruvate production in glycolysis , and requires pyruvate to the mitochondria in order to be oxidized by the citric acid cycle . The products of this process are carbon dioxide and water, and the energy transferred is used to make bonds between ADP and a third phosphate group to form ATP ( adenosine triphosphate ), by substrate-level phosphorylation , NADH and FADH 2 . The negative ΔG indicates that

2030-460: Is the process by which biological fuels are oxidized in the presence of an inorganic electron acceptor , such as oxygen , to drive the bulk production of adenosine triphosphate (ATP) , which contains energy. Cellular respiration may be described as a set of metabolic reactions and processes that take place in the cells of organisms to convert chemical energy from nutrients into ATP, and then release waste products . Cellular respiration

2100-843: Is to treat ferrous sulfide with a strong acid in a Kipp generator : For use in qualitative inorganic analysis , thioacetamide is used to generate H 2 S : Many metal and nonmetal sulfides, e.g. aluminium sulfide , phosphorus pentasulfide , silicon disulfide liberate hydrogen sulfide upon exposure to water: This gas is also produced by heating sulfur with solid organic compounds and by reducing sulfurated organic compounds with hydrogen. It can also be produced by mixing ammonium thiocyanate to concentrated sulphuric acid and adding water to it. Hydrogen sulfide can be generated in cells via enzymatic or non-enzymatic pathways. Three enzymes catalyze formation of H 2 S : cystathionine γ-lyase (CSE), cystathionine β-synthetase (CBS), and 3-mercaptopyruvate sulfurtransferase (3-MST). CBS and CSE are

2170-529: Is typically removed by amine gas treating technologies. In such processes, the hydrogen sulfide is first converted to an ammonium salt, whereas the natural gas is unaffected. The bisulfide anion is subsequently regenerated by heating of the amine sulfide solution. Hydrogen sulfide generated in this process is typically converted to elemental sulfur using the Claus Process . The underground mine gas term for foul-smelling hydrogen sulfide-rich gas mixtures

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2240-508: Is usually considered sour if there are more than 5.7 milligrams of H 2 S per cubic meter of natural gas, which is equivalent to approximately 4 ppm by volume under standard temperature and pressure. However, this threshold varies by country, state, or even agency or application. For instance, the Texas Railroad Commission considers a sour gas pipeline one that carries gas over 100 ppm by volume of H 2 S. However,

2310-521: The Texas Commission on Environmental Quality has historically defined sour gas for upstream operations – which requires permitting, reporting, and possibly additional emission controls – as gas that contains more than 24 ppm by volume. Natural gas that does not contain significant amounts of hydrogen sulfide is called "sweet gas". Although the terms " acid gas " and "sour gas" are sometimes used interchangeably, strictly speaking,

2380-587: The hydrosulfide ion HS . Hydrogen sulfide and its solutions are colorless. When exposed to air, it slowly oxidizes to form elemental sulfur, which is not soluble in water. The sulfide anion S is not formed in aqueous solution. At pressures above 90 GPa ( gigapascal ), hydrogen sulfide becomes a metallic conductor of electricity. When cooled below a critical temperature this high-pressure phase exhibits superconductivity . The critical temperature increases with pressure, ranging from 23 K at 100 GPa to 150 K at 200 GPa. If hydrogen sulfide

2450-462: The pyruvate is oxidized. The overall reaction can be expressed this way: Starting with glucose, 1 ATP is used to donate a phosphate to glucose to produce glucose 6-phosphate . Glycogen can be converted into glucose 6-phosphate as well with the help of glycogen phosphorylase . During energy metabolism, glucose 6-phosphate becomes fructose 6-phosphate . An additional ATP is used to phosphorylate fructose 6-phosphate into fructose 1,6-bisphosphate by

2520-400: The 10 protons from oxidizing NADH would produce 2.72 ATP (instead of 2.5) and the 6 protons from oxidizing succinate or ubiquinol would produce 1.64 ATP (instead of 1.5). This is consistent with experimental results within the margin of error described in a recent review. The total ATP yield in ethanol or lactic acid fermentation is only 2 molecules coming from glycolysis , because pyruvate

2590-421: The ATP production from the slower aerobic respiration, so fermentation may be used by a cell even before the oxygen levels are depleted, as is the case in sports that do not require athletes to pace themselves, such as sprinting . Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor, such as oxygen, to produce large amounts of energy and drive

2660-475: The CO 2 generated annually by terrestrial ecosystems . Glycolysis is a metabolic pathway that takes place in the cytosol of cells in all living organisms. Glycolysis can be literally translated as "sugar splitting", and occurs regardless of oxygen's presence or absence. In aerobic conditions, the process converts one molecule of glucose into two molecules of pyruvate (pyruvic acid), generating energy in

2730-513: The Krebs cycle. However, if oxygen is not present, fermentation of the pyruvate molecule will occur. In the presence of oxygen, when acetyl-CoA is produced, the molecule then enters the citric acid cycle (Krebs cycle) inside the mitochondrial matrix, and is oxidized to CO 2 while at the same time reducing NAD to NADH . NADH can be used by the electron transport chain to create further ATP as part of oxidative phosphorylation. To fully oxidize

2800-466: The addition of two protons, water is formed. The table below describes the reactions involved when one glucose molecule is fully oxidized into carbon dioxide. It is assumed that all the reduced coenzymes are oxidized by the electron transport chain and used for oxidative phosphorylation. Although there is a theoretical yield of 38 ATP molecules per glucose during cellular respiration, such conditions are generally not realized because of losses such as

2870-557: The bottom of the ocean., as well as in anoxic soils or sediment in wetland ecosystems. In July 2019, a scientific study of Kidd Mine in Canada discovered sulfur-breathing organisms which live 7900 feet (2400 meters) below the surface. These organisms are also remarkable because they consume minerals such as pyrite as their food source. Sour gas Sour gas is natural gas or any other gas containing significant amounts of hydrogen sulfide (H 2 S). Natural gas

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2940-463: The bulk production of ATP. Anaerobic respiration is used by microorganisms, either bacteria or archaea , in which neither oxygen (aerobic respiration) nor pyruvate derivatives (fermentation) is the final electron acceptor. Rather, an inorganic acceptor such as sulfate ( SO 2− 4 ), nitrate ( NO − 3 ), or sulfur (S) is used. Such organisms could be found in unusual places such as underwater caves or near hydrothermal vents at

3010-540: The burial of organic material rapidly leads to the production of anaerobic digestion within the waste mass and, with the humid atmosphere and relatively high temperature that accompanies biodegradation , biogas is produced as soon as the air within the waste mass has been reduced. If there is a source of sulfate bearing material, such as plasterboard or natural gypsum (calcium sulfate dihydrate), under anaerobic conditions sulfate reducing bacteria converts this to hydrogen sulfide. These bacteria cannot survive in air but

3080-410: The cell. This serves the purpose of oxidizing the electron carriers so that they can perform glycolysis again and removing the excess pyruvate. Fermentation oxidizes NADH to NAD so it can be re-used in glycolysis. In the absence of oxygen, fermentation prevents the buildup of NADH in the cytoplasm and provides NAD for glycolysis. This waste product varies depending on the organism. In skeletal muscles,

3150-460: The conversion of pyruvate to acetyl-CoA, one molecule of NADH and one molecule of CO 2 is formed. The citric acid cycle is also called the Krebs cycle or the tricarboxylic acid cycle . When oxygen is present, acetyl-CoA is produced from the pyruvate molecules created from glycolysis. Once acetyl-CoA is formed, aerobic or anaerobic respiration can occur. When oxygen is present, the mitochondria will undergo aerobic respiration which leads to

3220-589: The corresponding metal sulfides. Oxidic ores are sometimes treated with hydrogen sulfide to give the corresponding metal sulfides which are more readily purified by flotation . Metal parts are sometimes passivated with hydrogen sulfide. Catalysts used in hydrodesulfurization are routinely activated with hydrogen sulfide. Hydrogen sulfide was a reagent in the qualitative inorganic analysis of metal ions. In these analyses, heavy metal (and nonmetal ) ions (e.g., Pb(II), Cu(II), Hg(II), As(III)) are precipitated from solution upon exposure to H 2 S . The components of

3290-424: The cost of moving pyruvate (from glycolysis), phosphate, and ADP (substrates for ATP synthesis) into the mitochondria. All are actively transported using carriers that utilize the stored energy in the proton electrochemical gradient . The outcome of these transport processes using the proton electrochemical gradient is that more than 3 H are needed to make 1 ATP. Obviously, this reduces the theoretical efficiency of

3360-473: The cost of moving pyruvate and ADP into the mitochondrial matrix, and current estimates range around 29 to 30 ATP per glucose. Aerobic metabolism is up to 15 times more efficient than anaerobic metabolism (which yields 2 molecules of ATP per 1 molecule of glucose). However, some anaerobic organisms, such as methanogens are able to continue with anaerobic respiration , yielding more ATP by using inorganic molecules other than oxygen as final electron acceptors in

3430-516: The cysteine catabolic pathway. Dietary amino acids, such as methionine and cysteine serve as the primary substrates for the transulfuration pathways and in the production of hydrogen sulfide. Hydrogen sulfide can also be derived from proteins such as ferredoxins and Rieske proteins . Sulfate-reducing (resp. sulfur-reducing ) bacteria generate usable energy under low-oxygen conditions by using sulfates (resp. elemental sulfur) to oxidize organic compounds or hydrogen; this produces hydrogen sulfide as

3500-440: The electron transport chain. They share the initial pathway of glycolysis but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation. The post-glycolytic reactions take place in the mitochondria in eukaryotic cells , and in the cytoplasm in prokaryotic cells . Although plants are net consumers of carbon dioxide and producers of oxygen via photosynthesis , plant respiration accounts for about half of

3570-461: The equivalent of one glucose molecule, two acetyl-CoA must be metabolized by the Krebs cycle. Two low-energy waste products , H 2 O and CO 2 , are created during this cycle. The citric acid cycle is an 8-step process involving 18 different enzymes and co-enzymes. During the cycle, acetyl-CoA (2 carbons) + oxaloacetate (4 carbons) yields citrate (6 carbons), which is rearranged to a more reactive form called isocitrate (6 carbons). Isocitrate

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3640-534: The form of two net molecules of ATP . Four molecules of ATP per glucose are actually produced, but two are consumed as part of the preparatory phase . The initial phosphorylation of glucose is required to increase the reactivity (decrease its stability) in order for the molecule to be cleaved into two pyruvate molecules by the enzyme aldolase . During the pay-off phase of glycolysis, four phosphate groups are transferred to four ADP by substrate-level phosphorylation to make four ATP, and two NADH are produced when

3710-413: The help of phosphofructokinase . Fructose 1,6-biphosphate then splits into two phosphorylated molecules with three carbon chains which later degrades into pyruvate. Pyruvate is oxidized to acetyl-CoA and CO 2 by the pyruvate dehydrogenase complex (PDC). The PDC contains multiple copies of three enzymes and is located in the mitochondria of eukaryotic cells and in the cytosol of prokaryotes. In

3780-417: The main proponents of H 2 S biogenesis, which follows the trans-sulfuration pathway. These enzymes have been identified in a breadth of biological cells and tissues, and their activity is induced by a number of disease states. These enzymes are characterized by the transfer of a sulfur atom from methionine to serine to form a cysteine molecule. 3-MST also contributes to hydrogen sulfide production by way of

3850-470: The mitochondrial cristae . It comprises the electron transport chain that establishes a proton gradient (chemiosmotic potential) across the boundary of the inner membrane by oxidizing the NADH produced from the Krebs cycle. ATP is synthesized by the ATP synthase enzyme when the chemiosmotic gradient is used to drive the phosphorylation of ADP. The electrons are finally transferred to exogenous oxygen and, with

3920-576: The mitochondrial electron transport chain, which effectively reduces ATP generation and biochemical activity within cells. Hydrogen sulfide is mainly consumed as a precursor to elemental sulfur. This conversion, called the Claus process , involves partial oxidation to sulfur dioxide. The latter reacts with hydrogen sulfide to give elemental sulfur. The conversion is catalyzed by alumina. Many fundamental organosulfur compounds are produced using hydrogen sulfide. These include methanethiol , ethanethiol , and thioglycolic acid . Hydrosulfides can be used in

3990-473: The moist, warm, anaerobic conditions of buried waste that contains a high source of carbon – in inert landfills, paper and glue used in the fabrication of products such as plasterboard can provide a rich source of carbon – is an excellent environment for the formation of hydrogen sulfide. In industrial anaerobic digestion processes, such as waste water treatment or the digestion of organic waste from agriculture , hydrogen sulfide can be formed from

4060-588: The most common oxidizing agent is molecular oxygen (O 2 ). The chemical energy stored in ATP (the bond of its third phosphate group to the rest of the molecule can be broken allowing more stable products to form, thereby releasing energy for use by the cell) can then be used to drive processes requiring energy, including biosynthesis , locomotion or transportation of molecules across cell membranes . Aerobic respiration requires oxygen (O 2 ) in order to create ATP . Although carbohydrates , fats and proteins are consumed as reactants , aerobic respiration

4130-440: The numismatic value of a coin based on aesthetics, as the toning may produce thin-film interference , resulting in the coin taking on an attractive coloration. Coins can also be intentionally treated with hydrogen sulfide to induce toning, though artificial toning can be distinguished from natural toning, and is generally criticised among collectors. Hydrogen sulfide is most commonly obtained by its separation from sour gas , which

4200-477: The production of thiophenol . Upon combining with alkali metal bases, hydrogen sulfide converts to alkali hydrosulfides such as sodium hydrosulfide and sodium sulfide : Sodium sulfides are used in the paper making industry. Specifically, salts of SH break bonds between lignin and cellulose components of pulp in the Kraft process . As indicated above, many metal ions react with hydrogen sulfide to give

4270-399: The raw gas must be treated to remove those impurities to acceptable levels, commonly by an amine treatment process. The removed H 2 S is most often subsequently converted to by-product elemental sulfur in a Claus process or it can be treated in a wet sulfuric acid process unit where the by-product is sulfuric acid . Alternatively, the highly concentrated H 2 S gas, the by-product of

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4340-443: The reaction is exothermic ( exergonic ) and can occur spontaneously. The potential of NADH and FADH 2 is converted to more ATP through an electron transport chain with oxygen and protons (hydrogen ions) as the " terminal electron acceptors ". Most of the ATP produced by aerobic cellular respiration is made by oxidative phosphorylation . The energy released is used to create a chemiosmotic potential by pumping protons across

4410-432: The reduction of sulfate and the degradation of amino acids and proteins within organic compounds. Sulfates are relatively non-inhibitory to methane forming bacteria but can be reduced to H 2 S by sulfate reducing bacteria , of which there are several genera. A number of processes have been designed to remove hydrogen sulfide from drinking water . Hydrogen sulfide is commonly found in raw natural gas and biogas. It

4480-728: The resulting solid are then identified by their reactivity. Hydrogen sulfide is used to separate deuterium oxide, or heavy water , from normal water via the Girdler sulfide process . A suspended animation-like state has been induced in rodents with the use of hydrogen sulfide, resulting in hypothermia with a concomitant reduction in metabolic rate. Oxygen demand was also reduced, thereby protecting against hypoxia . In addition, hydrogen sulfide has been shown to reduce inflammation in various situations. Volcanoes and some hot springs (as well as cold springs ) emit some H 2 S . Hydrogen sulfide can be present naturally in well water, often as

4550-636: The sense of smell, creating temporary anosmia , so victims may be unaware of its presence until it is too late. Safe handling procedures are provided by its safety data sheet (SDS) . Since hydrogen sulfide occurs naturally in the body, the environment, and the gut, enzymes exist to metabolize it. At some threshold level, believed to average around 300–350 ppm, the oxidative enzymes become overwhelmed. Many personal safety gas detectors, such as those used by utility, sewage and petrochemical workers, are set to alarm at as low as 5 to 10 ppm and to go into high alarm at 15 ppm. Metabolism causes oxidation to sulfate, which

4620-506: The synthase assumes that the synthase translocates 9 protons, and produces 3 ATP, per rotation. The number of protons depends on the number of c subunits in the Fo c-ring , and it is now known that this is 10 in yeast Fo and 8 for vertebrates. Including one H for the transport reactions, this means that synthesis of one ATP requires 1 + 10/3 = 4.33 protons in yeast and 1 + 8/3 = 3.67 in vertebrates . This would imply that in human mitochondria

4690-410: The waste product is lactic acid . This type of fermentation is called lactic acid fermentation . In strenuous exercise, when energy demands exceed energy supply, the respiratory chain cannot process all of the hydrogen atoms joined by NADH. During anaerobic glycolysis, NAD regenerates when pairs of hydrogen combine with pyruvate to form lactate. Lactate formation is catalyzed by lactate dehydrogenase in

4760-434: The whole process and the likely maximum is closer to 28–30 ATP molecules. In practice the efficiency may be even lower because the inner membrane of the mitochondria is slightly leaky to protons. Other factors may also dissipate the proton gradient creating an apparently leaky mitochondria. An uncoupling protein known as thermogenin is expressed in some cell types and is a channel that can transport protons. When this protein

4830-460: Was discovered, Italian physician Bernardino Ramazzini hypothesized in his 1713 book De Morbis Artificum Diatriba that occupational diseases of sewer-workers and blackening of coins in their clothes may be caused by an unknown invisible volatile acid (moreover, in late 18th century toxic gas emanation from Paris sewers became a problem for the citizens and authorities). Although very pungent at first (it smells like rotten eggs), it quickly deadens

4900-482: Was used by the British Army as a chemical weapon during World War I . It was not considered to be an ideal war gas, partially due to its flammability and because the distinctive smell could be detected from even a small leak, alerting the enemy to the presence of the gas. It was nevertheless used on two occasions in 1916 when other gases were in short supply. Cellular respiration Cellular respiration

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