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45-415: It was noticed in 1935 that air contained more O than seawater; this was quantified in 1975 to 23.5‰, but later refined as 23.88‰ in 2005. The imbalance arises mainly as a result of respiration in plants and in animals . Due to thermodynamics of isotope reactions, respiration removes the lighter—hence more reactive—O in preference to O, increasing the relative amount of O in the atmosphere. The inequality

90-440: A tracer in sea water, with slight variations in chemistry being used to track a discrete "parcel" of water and determine its age. Plant respiration Cellular respiration 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

135-497: A Dole effect shift of -2-3‰ from the current value of 23.5‰ . The stability (to within 0.5‰) of the atmospheric O to O ratio with respect to sea surface waters since the last interglacial (the last 130 000 years), as derived from ice cores, suggests that terrestrial and marine productivity have varied together during this time period. Millennial variations of the Dole effect were found to be related to abrupt climate change events in

180-488: 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

225-458: 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

270-583: 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 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

315-411: A substrate. In this context, the oxidizing agent can be called an oxygenation reagent or oxygen-atom transfer (OAT) agent. Examples include MnO 4 ( permanganate ), CrO 4 ( chromate ), OsO 4 ( osmium tetroxide ), and especially ClO 4 ( perchlorate ). Notice that these species are all oxides . In some cases, these oxides can also serve as electron acceptors, as illustrated by

360-415: Is potassium dichromate , which does not pass the dangerous goods test of an oxidizing agent. The U.S. Department of Transportation defines oxidizing agents specifically. There are two definitions for oxidizing agents governed under DOT regulations. These two are Class 5 ; Division 5.1(a)1 and Class 5; Division 5.1(a)2. Division 5.1 "means a material that may, generally by yielding oxygen, cause or enhance

405-410: Is a substance in a redox chemical reaction that gains or " accepts "/"receives" an electron from a reducing agent (called the reductant , reducer , or electron donor ). In other words, an oxidizer is any substance that oxidizes another substance. The oxidation state , which describes the degree of loss of electrons , of the oxidizer decreases while that of the reductant increases; this

450-780: 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

495-442: Is balanced by photosynthesis . Photosynthesis emits oxygen with the same isotopic composition (i.e. the ratio between O and O ) as the water (H 2 O) used in the reaction, which is independent of the atmospheric ratio. Thus when atmospheric O levels are high enough, photosynthesis will act as a reducing factor. However, as a complicating factor, the degree of fractionation (i.e. change in isotope ratio) occurring due to photosynthesis

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540-428: Is expressed by saying that oxidizers "undergo reduction" and "are reduced" while reducers "undergo oxidation" and "are oxidized". Common oxidizing agents are oxygen , hydrogen peroxide , and the halogens . In one sense, an oxidizing agent is a chemical species that undergoes a chemical reaction in which it gains one or more electrons. In that sense, it is one component in an oxidation–reduction (redox) reaction. In

585-520: 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

630-476: 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

675-482: Is not entirely dependent on the water drawn up by the plant, as fractionation can occur as a result of preferential evaporation of H 2 O - water bearing lighter oxygen isotopes, and other small but significant processes. Since evaporation causes oceanic and terrestrial waters to have a different ratio of O to O, the Dole effect will reflect the relevant importances of land-based and marine photosynthesis. The complete removal of land-based productivity would result in

720-442: 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

765-481: Is one of the key ways 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

810-492: Is the ferrocenium ion Fe(C 5 H 5 ) 2 , which accepts an electron to form Fe(C 5 H 5 ) 2 . One of the strongest acceptors commercially available is " Magic blue ", the radical cation derived from N(C 6 H 4 -4-Br) 3 . Extensive tabulations of ranking the electron accepting properties of various reagents (redox potentials) are available, see Standard electrode potential (data page) . In more common usage, an oxidizing agent transfers oxygen atoms to

855-447: 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

900-462: 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

945-400: 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

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990-421: 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

1035-475: 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

1080-513: 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

1125-525: The North Atlantic region during the last 60 kyr (1kyr=1000years). High correlations of the Dole effect to speleothem δO, an indicator for monsoon precipitation, suggest that it is subject to changes in low-latitude terrestrial productivity. Orbital scale variations of the Dole effect, characterized by periods of 20-100 kyr, respond strongly to Earth's orbital eccentricity and precession , but not obliquity . The Dole effect can also be applied as

1170-466: 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

1215-552: 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. Oxidizing agent An oxidizing agent (also known as an oxidant , oxidizer , electron recipient , or electron acceptor )

1260-463: 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

1305-410: 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,

1350-510: The combustion of other materials." Division 5.(a)1 of the DOT code applies to solid oxidizers "if, when tested in accordance with the UN Manual of Tests and Criteria (IBR, see § 171.7 of this subchapter), its mean burning time is less than or equal to the burning time of a 3:7 potassium bromate/cellulose mixture." 5.1(a)2 of the DOT code applies to liquid oxidizers "if, when tested in accordance with

1395-402: The conversion of MnO 4 to MnO 4 ,ie permanganate to manganate . The dangerous goods definition of an oxidizing agent is a substance that can cause or contribute to the combustion of other material. By this definition some materials that are classified as oxidizing agents by analytical chemists are not classified as oxidizing agents in a dangerous materials sense. An example

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1440-460: 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

1485-424: 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

1530-473: 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

1575-440: 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

1620-461: 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

1665-534: 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

1710-413: 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

1755-470: 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

1800-588: 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

1845-443: 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

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1890-441: The second sense, an oxidizing agent is a chemical species that transfers electronegative atoms, usually oxygen, to a substrate. Combustion , many explosives, and organic redox reactions involve atom-transfer reactions. Electron acceptors participate in electron-transfer reactions . In this context, the oxidizing agent is called an electron acceptor and the reducing agent is called an electron donor . A classic oxidizing agent

1935-506: 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

1980-410: 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

2025-434: 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

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