What are the reactants and products of cellular respiration

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What are the reactants and products of cellular respiration

Cellular respiration is divided into two parts: aerobic cellular respiration, and anaerobic cellular respiration. Aerobic cellular respiration is the process by which all organisms use C6H12O6 (glucose) and 6O2 to make 6CO2, 6H2O and 36 ATP. It is called aerobic because it requires oxygen.The chemical equation for aerobic cellular respiration is:C6H12O6 + 6O2 ---> 6CO2 + 6H2O + 36 ATPIn this reaction, C6H12O6 + 6O2 are the reactants; and 6CO2 + 6H2O + 36 ATP are the products. The waste products of this reaction are 6CO2 and 6H2O.The primary function of aerobic cellular respiration is to produce ATP for the cell.Aerobic cellular respiration occurs in the cytoplasm and in the cell's mitochondria.Three interesting facts about aerobic cellular respiration:- Aerobic cellular respiration breaks down the glucose molecules that are formed in photosynthesis so that the cell can use it for energy.- When trying to memorize the chemical equation for aerobic cellular respiration, it helps to know that the chemical equation of aerobic cellular respiration is the chemical opposite of the chemical equation for photosynthesis. You only need to learn one, and to find the other all you have to do is flip the reactants and products.- Aerobic cellular respiration has four steps: Glycolysis, the Intermediate Step, the Kreb's Cycle, and the Electron Transport Chain. Glycolysis occurs in the cytoplasm, and glucose is broken down to make 2 ATP. The Intermediate Step occurs in the mitchondria, and 3 carbon pyruvic acid molecules are converted to 2 carbon molecules. The Kreb's Cycle occurs in the mitochondria, and each 2 carbon molecule goes through a cycle where carbons are added and released. 2 ATP are produced, and Hydrogen ions are collected. Finally, the Electron Transport Chain occurs in the cristae of the mitochondria(cristae - a folded membrane inside the mitochondria that increases the surface area for production of more ATP). The H+ collected in the Kreb's Cycle are used to make approximately 28-32 ATP.Anaerobic Cellular RespirationAnaerobic cellular respiration is the process by which all organisms use C6H12O6 to make CO2 and 2 ATP. It is called anaerobic because it doesn't require oxygen. The process of anaerobic cellular respiration is different in plants and animals. The chemical equation for anaerobic cellular respiration in animals is:C6H12O6 ---> CO2 + lactic acid + 2 ATPIn this reaction (called lactic acid fermentation), C6H12O6 is the reactant and CO2 + lactic acid + 2 ATP are the products. CO2 and lactic acid are the waste products.The chemical equation for anaerobic cellular respiration in plants is:C6H12O6 ---> CO2 + ethanol + 2 ATPIn this reaction (called alcoholic fermentation), C6H12O6 is the reactant and CO2 + ethanol + 2 ATP are the products. CO2 and ethanol are the waste products.The primary function of anaerobic cellular respiration is to continue the production of ATP for the cell, even when oxygen is unavailable.Anaerobic respiration only occurs in the cytoplasm.Three interesting facts about anaerobic cellular respiration:- Anaerobic cellular respiration is considered less effiecient than aerobic cellular respiration, since anaerobic only produces 2 ATP per glucose molecule while aerobic cellular respiration produces 36-38 ATP per glucose molecule.- Anaerobic cellular respiration only occurs in the cytoplasm because only the Glycolysis step occurs; hence the reason why only 2 ATP are produced.- One example of anaerobic cellular respiration in animals is when humans exercise. When we breathe heavily during intense exercise, we aren't taking in enough oxygen for aerobic cellular respiration to occur; and therefore lactic acid fermentation takes place. Lactic acid production is what causes your muscles to ache after a hard workout. Cellular respiration is the process through which cells convert sugars into energy. To create ATP and other forms of energy to power cellular reactions, cells require fuel and an electron acceptor which drives the chemical process of turning energy into a useable form. Eukaryotes, including all multicellular organisms and some single-celled organisms, use aerobic respiration to produce energy. Aerobic respiration uses oxygen ? the most powerful electron acceptor available in nature. Aerobic respiration is an extremely efficient process allows eukaryotes to have complicated life functions and active lifestyles. However, it also means that they require a constant supply of oxygen, or they will be unable to obtain energy to stay alive. Prokaryotic organisms such as bacteria and archaebacteria can use other forms of respiration, which are somewhat less efficient. This allows them to live in environments where eukaryotic organisms could not, because they do not require oxygen. Examples of different pathways for how sugars are broken down by organisms are illustrated below: More detailed articles on aerobic respiration and anaerobic respiration can be found on this site. Here we will give an overview of the different types of cellular respiration. The equation for aerobic respiration shows glucose being combined with oxygen and ADP to produce carbon dioxide, water, and ATP: C6H12O6 (glucose)+ 6O2 + 36 ADP (depleted ATP) + 36 Pi (phosphate groups) 6CO2 + 6H2O + 36 ATP You can see that once it is completely broken down, the carbon molecules of glucose are exhaled as six molecules of carbon dioxide. In lactic acid fermentation, one molecule of glucose is broken down into two molecules of lactic acid. The chemical energy that was stored in the broken glucose bonds is moved into bonds between ADP and a phosphate group. C6H12O6 (glucose) + 2 ADP (depleted ATP) + 2 Pi (phosphate groups) 2 CH3CHOHCOOH (lactic acid) + 2 ATP Alcohol fermentation is similar to lactic acid fermentation in that oxygen is not the final electron acceptor. Here, instead of oxygen, the cell uses a converted form of pyruvate to accept the final electrons. This creates ethyl alcohol, which is what is found in alcoholic beverages. Brewers and distillers use yeast cells to create this alcohol, which are very good at this form of fermentation. C6H12O6 (glucose) + 2 ADP (depleted ATP) + 2 Pi (phosphate groups) 2 C2H5OH (ethyl alcohol) + 2 CO2 + 2 ATP Glycolysis is the only step which is shared by all types of respiration. In glycolysis, a sugar molecule such as glucose is split in half, generating two molecules of ATP. The equation for glycolysis is: C6H12O6 (glucose) + 2 NAD+ + 2 ADP + 2 Pi 2 CH3COCOO- + 2 NADH + 2 ATP + 2 H2O + 2H+ The name "glycolysis" comes from the Greek "glyco," for "sugar" and "lysis" for "to split." This may help you to remember that glycolysis it the process of splitting a sugar. In most pathways, glycolysis starts with glucose, which is then split into two molecules of pyruvic acid. These two molecules of pyruvic acid are then processed further to form different end products, such as ethyl alcohol or lactic acid. Reduction is the next part of the process. In chemical terms, to "reduce" a molecule means to add electrons to it. In the case of lactic acid fermentation, NADH donates an electron to pyruvic acid, resulting in the end products of lactic acid and NAD+. This is helpful to the cell because NAD+ is necessary for glycolysis. In the case of alcoholic fermentation, pyruvic acid undergoes an additional step in which it loses an atom of carbon in the form of CO2. The resulting intermediate molecule, called acetaldehyde, is then reduced to produce NAD+ plus ethyl alcohol. Aerobic respiration takes these processes to another level. Instead of directly reducing intermediates of the Krebs cycle, aerobic respiration uses oxygen as the final electron receptor. But first, the electrons and protons bound to electron carriers (such as NADH), are processed through the electron transport chain. This chain of proteins within the mitochondrial membrane uses the energy from these electrons to pump protons to one side of the membrane. This creates an electromotive force, which is utilized by the protein complex ATP synthase phosphorylate a large number of ATD molecules, creating ATP. The main product of any cellular respiration is the molecule adenosine triphosphate (ATP). This molecule stores the energy released during respiration and allows the cell to transfer this energy to various parts of the cell. ATP is used by a number of cellular components as a source of energy. For example, an enzyme may need energy from ATP to combine two molecules. ATP is also commonly used on transporters, which are proteins that function to move molecules across the cell membrane. Carbon dioxide is a universal product created by cellular respiration. Typically, carbon dioxide is considered a waste product and must be removed. In an aqueous solution, carbon dioxide creates acidic ions. This can drastically lower the pH of the cell, and eventually will cause normal cellular functions to cease. To avoid this, cells must actively expel carbon dioxide. While ATP and carbon dioxide are regularly produced by all forms of cellular respiration, different types of respiration rely on different molecules to be the final acceptors of the electrons used in the process. All cells need to be able to obtain and transport energy to power their life functions. For cells to continue living, they must be able to operate essential machinery, such as pumps in their cell membranes which maintain the cell's internal environment in a way that's suitable for life. The most common "energy currency" of cells is ATP ? a molecule which stores a lot of energy in its phosphate bonds. These bonds can be broken to release that energy and bring about changes to other molecules, such as those needed to power cell membrane pumps. Because ATP is not stable over long periods of time, it is not used for long-term energy storage. Instead, sugars and fats are used as a long-term form of storage, and cells must constantly process those molecules to produce new ATP. This is the process of respiration. The process of aerobic respiration produces a huge amount of ATP from each molecule of sugar. In fact, each molecule of sugar digested by a plant or animal cell yields 36 molecules of ATP! By comparison, fermentation usually only produces 2-4 molecules of ATP. Anaerobic respiration processes used by bacteria and archaebacteria yield smaller amounts of ATP, but they can take place without oxygen. Below, we'll discuss how different types of cellular respiration produce ATP. Eukaryotic organisms perform cellular respiration in their mitochondria ? organelles that are designed to break down sugars and produce ATP very efficiently. Mitochondria are often called "the powerhouse of the cell" because they are able to produce so much ATP! Aerobic respiration is so efficient because oxygen is the most powerful electron acceptor found in nature. Oxygen "loves" electrons ? and its love of electrons "pulls" them through the electron transport chain of the mitochondria. The specialized anatomy of the mitochondria ? which bring together all the necessary reactants for cellular respiration in a small, membrane-bound space within the cell ? also contributes to the high efficiency of aerobic respiration. In the absence of oxygen, most eukaryotic cells can also perform different types of anaerobic respiration, such as lactic acid fermentation. However, these processes do not produce enough ATP to maintain the cell's life functions, and without oxygen, cells will eventually die or cease to function. Fermentation is the name given to many different types of anaerobic respiration, which are performed by different species of bacteria and archaebacteria, and by some eukaryotic cells in the absence of oxygen. These processes can use a variety of electron acceptors and produce a variety of byproducts. A few types of fermentation are: Alcoholic fermentation ? This type of fermentation, performed by yeast cells and some other cells, metabolizes sugar and produces alcohol and carbon dioxide as byproducts. This is why beers are fizzy: during fermentation, their yeasts release both carbon dioxide gas, which forms bubbles and ethyl alcohol. Lactic acid fermentation ? This type of fermentation is performed by human muscle cells in the absence of oxygen, and by some bacteria. Lactic acid fermentation is actually used by humans to make yogurt. To make yogurt, harmless bacteria are grown in milk. The lactic acid produced by these bacteria gives yogurt its distinctive sharp-sour taste and also reacts with milk proteins to create a thick, creamy texture. Proprionic acid fermentation ? This type of fermentation is performed by some bacteria, and is used to make swiss cheese. Proprionic acid is responsible for the distinctive sharp, nutty flavor of Swiss cheese. The gas bubbles created by these bacteria are responsible for the holes found in the cheese. Acetogenesis ? Acetogenesis is a type of fermentation performed by bacteria, which produces acetic acid as its byproduct. Acetic acid is the distinctive ingredient in vinegar which gives it its sharp, sour taste and smell. Interestingly, the bacteria that produce acetic acid use ethyl alcohol as their fuel. This means that to produce vinegar, a sugar-containing solution must be first fermented with yeast to produce alcohol, then fermented again with bacteria that turn the alcohol into acetic acid! Methanogenesis is a unique type of anaerobic respiration that can only be performed by archaebacteria. In methanogenesis, a fuel source carbohydrate is broken down to produce carbon dioxide and methane. Methanogenesis is performed by some symbiotic bacteria in the digestive tracts of humans, cows, and some other animals. Some of these bacteria are able to digest cellulose, a sugar found in plants that cannot be broken down through cellular respiration. Symbiotic bacteria allow cows and other animals to obtain some energy from these otherwise undigestible sugars! Metabolic reactions in the cells of organisms converting chemical energy from oxygen molecules or nutrients into adenosine triphosphate (ATP) while releasing waste byproducts. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: "Cellular respiration" ? news ? newspapers ? books ? scholar ? JSTOR (September 2014) (Learn how and when to remove this template message) Typical eukaryotic cell Cellular respiration is a set of metabolic reactions and processes that take place in the cells of organisms to convert chemical energy from oxygen molecules[1] or nutrients into adenosine triphosphate (ATP), and then release waste products.[2] The reactions involved in respiration are catabolic reactions, which break large molecules into smaller ones, releasing energy because weak high-energy bonds, in particular in molecular oxygen,[3] are replaced by stronger bonds in the products. Respiration 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 clearly does not resemble one when it occurs in a living cell 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 the most common oxidizing agent providing most of the chemical energy is molecular oxygen (O2).[1] 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 transport of molecules across cell membranes. Aerobic respiration Aerobic respiration requires oxygen (O2) in order to create ATP. Although carbohydrates, fats, and proteins are consumed as reactants, aerobic respiration is the preferred method of pyruvate breakdown in glycolysis, and requires pyruvate to the mitochondria in order to be fully oxidized by the citric acid cycle. The products of this process are carbon dioxide and water, and the energy transferred is used to break bonds in ADP to add a third phosphate group to form ATP (adenosine triphosphate), by substrate-level phosphorylation, NADH and FADH2 Simplified reaction: C6H12O6 (s) + 6 O2 (g) 6 CO2 (g) + 6 H2O (l) + heat G = -2880 kJ per mol of C6H12O6 The negative G indicates that the reaction can occur spontaneously. The potential of NADH and FADH2 is converted to more ATP through an electron transport chain with oxygen and protons (hydrogen) as the "terminal electron acceptors".[1] Most of the ATP produced by aerobic cellular respiration is made by oxidative phosphorylation. The energy of O2 [1] released is used to create a chemiosmotic potential by pumping protons across 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).[4] However, this maximum yield is never quite reached because of losses due to leaky membranes as well as the cost of moving pyruvate and ADP into the mitochondrial matrix, and current estimates range around 29 to 30 ATP per glucose.[4] Aerobic metabolism is up to 15 times more efficient than anaerobic metabolism (which yields 2 molecules ATP per 1 molecule glucose) because the double bond in O2 is of higher energy than other double bonds or pairs of single bonds in other common molecules in the biosphere.[3] However, some anaerobic organisms, such as methanogens are able to continue with anaerobic respiration, yielding more ATP by using other inorganic molecules (not oxygen) of high energy as final electron acceptors in 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. Glycolysis Out of the cytoplasm it goes into the Krebs cycle with the acetyl CoA. It then mixes with CO2 and makes 2 ATP, NADH, and FADH. From there the NADH and FADH go into the NADH reductase, which produces the enzyme. The NADH pulls the enzyme's electrons to send through the electron transport chain. The electron transport chain pulls H+ ions through the chain. From the electron transport chain, the released hydrogen ions make ADP for an end result of 32 ATP. O2 provides most of the energy for the process and combines with protons and the electrons to make water. Lastly, ATP leaves through the ATP channel and out of the mitochondria. Main article: Glycolysis 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",[5] and occurs with or without the presence of oxygen. In aerobic conditions, the process converts one molecule of glucose into two molecules of pyruvate (pyruvic acid), generating energy in the form of two net molecules of ATP. Four molecules of ATP per glucose are actually produced, however, 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 ADP by substrate-level phosphorylation to make four ATP, and two NADH are produced when the pyruvate is oxidized. The overall reaction can be expressed this way: Glucose + 2 NAD+ + 2 Pi + 2 ADP 2 pyruvate + 2 H+ + 2 NADH + 2 ATP + 2 H+ + 2 H2O + energy 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 the help of phosphofructokinase. Fructose 1,6-biphosphate then splits into two phosphorylated molecules with three carbon chains which later degrades into pyruvate. Oxidative decarboxylation of pyruvate Main article: Pyruvate decarboxylation Pyruvate is oxidized to acetyl-CoA and CO2 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 the conversion of pyruvate to acetyl-CoA, one molecule of NADH and one molecule of CO2 is formed. Citric acid cycle Main article: Citric acid cycle This 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.[6] When oxygen is present, the mitochondria will undergo aerobic respiration which leads to 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 CO2 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 the equivalent of one glucose molecule, two acetyl-CoA must be metabolized by the Krebs cycle. Two low-energy waste products, H2O and CO2, are created during this cycle. The citric acid cycle is an 8-step process involving 18 different enzymes and co-enzymes.[6] 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 is modified to become -ketoglutarate (5 carbons), succinyl-CoA, succinate, fumarate, malate, and, finally, oxaloacetate. The net gain from one cycle is 3 NADH and 1 FADH2 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 FADH2, and 2 ATP. Oxidative phosphorylation Main articles: Oxidative phosphorylation, Electron transport chain, Electrochemical gradient, and ATP synthase In eukaryotes, oxidative phosphorylation occurs in 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 electron transfer is driven by the chemical energy of exogenous oxygen[1] and, with the addition of two protons, water is formed. Efficiency of ATP production 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. Step coenzyme yield ATP yield Source of ATP Glycolysis preparatory phase -2 Phosphorylation of glucose and fructose 6-phosphate uses two ATP from the cytoplasm. Glycolysis pay-off phase 4 Substrate-level phosphorylation 2 NADH 3 or 5 Oxidative phosphorylation : Each NADH produces net 1.5 ATP (instead of usual 2.5) due to NADH transport over the mitochondrial membrane Oxidative decarboxylation of pyruvate 2 NADH 5 Oxidative phosphorylation Krebs cycle 2 Substrate-level phosphorylation 6 NADH 15 Oxidative phosphorylation 2 FADH2 3 Oxidative phosphorylation Total yield 30 or 32 ATP From the complete oxidation of one glucose molecule to carbon dioxide and oxidation of all the reduced coenzymes. 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 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. Pyruvate is taken up by a specific, low Km transporter to bring it into the mitochondrial matrix for oxidation by the pyruvate dehydrogenase complex. The phosphate carrier (PiC) mediates the electroneutral exchange (antiport) of phosphate (H2PO4-; Pi) for OH- or symport of phosphate and protons (H+) across the inner membrane, and the driving force for moving phosphate ions into the mitochondria is the proton motive force. The ATP-ADP translocase (also called adenine nucleotide translocase, ANT) is an antiporter and exchanges ADP and ATP across the inner membrane. The driving force is due to the ATP (-4) having a more negative charge than the ADP (-3), and thus it dissipates some of the electrical component of 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 the whole process and the likely maximum is closer to 28?30 ATP molecules.[4] In practice the efficiency may be even lower because the inner membrane of the mitochondria is slightly leaky to protons.[7] 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 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. Stoichiometry of aerobic respiration and most known fermentation types in eucaryotic cell. [8] Numbers in circles indicate counts of carbon atoms in molecules, C6 is glucose C6H12O6, C1 carbon dioxide CO2. Mitochondrial outer membrane is omitted. 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 [8], because: ATP : NADH+H+ and ATP : FADH2 ratios during the oxidative phosphorylation appear to be not 3 and 2, but 2.5 and 1.5 respectively. Unlike in the substratelevel phosphorylation, the stoichiometry here is difficult to establish. ATP synthase produces 1 ATP / 3 H+. However the exchange of matrix ATP for cytosolic ADP and Pi (antiport with OH- or symport with H+) mediated by ATP?ADP translocase and phosphate carrier consumes 1 H+ / 1 ATP as a result of regeneration of the transmembrane potential changed during this transfer, so the net ratio is 1 ATP : 4 H+. The mitochondrial electron transport chain proton pump transfers across the inner membrane 10 H+ / 1 NADH+H+ (4 + 2 + 4) or 6 H+ / 1 FADH2 (2 + 4). So the final stoichiometry is 1 NADH+H+ : 10 H+ : 10/4 ATP = 1 NADH+H+ : 2.5 ATP 1 FADH2 : 6 H+ : 6/4 ATP = 1 FADH2 : 1.5 ATP ATP : NADH+H+ coming from glycolysis ratio during the oxidative phosphorylation is 1.5, as for FADH2, if hydrogen atoms (2H++2e-) are transferred from cytosolic NADH+H+ to mitochondrial FAD by the glycerol phosphate shuttle located in the inner mitochondrial membrane. 2.5 in case of malate-aspartate shuttle transferring hydrogen atoms from cytosolic NADH+H+ to mitochondrial NAD+ So finally we have, per molecule of glucose Substrate-level phosphorylation: 2 ATP from glycolysis + 2 ATP (directly GTP) from Krebs cycle Oxidative phosphorylation 2 NADH+H+ from glycolysis: 2 ? 1.5 ATP (if glycerol phosphate shuttle transfers hydrogen atoms) or 2 ? 2.5 ATP (malateaspartate shuttle) 2 NADH+H+ from the oxidative decarboxylation of pyruvate and 6 from Krebs cycle: 8 ? 2.5 ATP 2 FADH2 from the Krebs cycle: 2 ? 1.5 ATP 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 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[9] and 8 for vertebrates.[10] 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 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.[11] The total ATP yield in ethanol or lactic acid fermentation is only 2 molecules coming from glycolysis, because pyruvate is not transferred to the mitochondrion and finally oxidized to the carbon dioxide (CO2), but reduced to ethanol or lactic acid in the cytoplasm.[8] Fermentation Main article: Fermentation 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 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, 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 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 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. This is because most of the energy of aerobic respiration derives from O2 with its relatively weak, high-energy double bond.[3][1] Glycolytic ATP, however, is created 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 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. Anaerobic respiration Main article: Anaerobic respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of a high-energy inorganic electron acceptor (such as oxygen[1]) to produce large amounts of energy, to drive the bulk production of ATP. Anaerobic respiration is used by some microorganisms in which neither oxygen (aerobic respiration) nor pyruvate derivatives (fermentation) is the high-energy final electron acceptor. Rather, an inorganic acceptor such as sulfate (SO42-), nitrate (NO3?), or sulfur (S) is used.[12] Such organisms are typically found in unusual places such as underwater caves or near hydrothermal vents at the bottom of the ocean. In July 2019, a scientific study of Kidd Mine in Canada discovered sulfur-breathing organisms which live 7900 feet below the surface, and which breathe sulfur in order to survive. These organisms are also remarkable due to consuming minerals such as pyrite as their food source. [13][14][15] See also Maintenance respiration: maintenance as a functional component of cellular respiration Microphysiometry Pasteur point Respirometry: research tool to explore cellular respiration Tetrazolium chloride: cellular respiration indicator Complex 1: NADH:ubiquinone oxidoreductes References ^ a b c d e f g Schmidt-Rohr, K. (2020). "Oxygen Is the High-Energy Molecule Powering Complex Multicellular Life: Fundamental Corrections to Traditional Bioenergetics" ACS Omega 5: 2221-2233. ^ Bailey, Regina. "Cellular Respiration". Archived from the original on 2012-05-05. ^ a b c Schmidt-Rohr, K. (2015). "Why Combustions Are Always Exothermic, Yielding About 418 kJ per Mole of O2", J. Chem. Educ. 92: 2094-2099. ^ a b c Rich, P. R. (2003). "The molecular machinery of Keilin's respiratory chain". Biochemical Society Transactions. 31 (Pt 6): 1095?1105. doi:10.1042/BST0311095. PMID 14641005. ^ Reece1 Urry2 Cain3 Wasserman4 Minorsky5 Jackson6, Jane1 Lisa2 Michael3 Steven4 Peter5 Robert6 (2010). Campbell Biology Ninth Edition. Pearson Education, Inc. p. 168. ^ a b "Cellular Respiration" (PDF). Archived (PDF) from the original on 2017-05-10. ^ Porter, R.; Brand, M. (1 September 1995). "Mitochondrial proton conductance and H+/O ratio are independent of electron transport rate in isolated hepatocytes". The Biochemical Journal (Free full text). 310 (Pt 2): 379?382. doi:10.1042/bj3100379. ISSN 0264-6021. PMC 1135905. PMID 7654171. ^ a b c Stryer, Lubert (1995). Biochemistry (fourth ed.). New York ? Basingstoke: W. H. Freeman and Company. ISBN 978-0716720096. ^ Stock D, Leslie AG, Walker JE (1999). "Molecular architecture of the rotary motor in ATP synthase". Science. 286 (5445): 1700?5. doi:10.1126/science.286.5445.1700. PMID 10576729.CS1 maint: uses authors parameter (link) ^ Watt, I.N., Montgomery, M.G., Runswick, M.J., Leslie, A.G.W., Walker, J.E. (2010). "Bioenergetic Cost of Making an Adenosine Triphosphate Molecule in Animal Mitochondria". Proc. Natl. Acad. Sci. USA. 107 (39): 16823?16827. doi:10.1073/pnas.1011099107. PMC 2947889. PMID 20847295.CS1 maint: uses authors parameter (link) ^ P.Hinkle (2005). "P/O ratios of mitochondrial oxidative phosphorylation". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1706 (1?2): 1?11. doi:10.1016/j.bbabio.2004.09.004. PMID 15620362. ^ Lumen Boundless Microbiology. "Anaerobic Respiration-Electron Donors and Acceptors in Anaerobic Respiration". courses.. . Retrieved November 19, 2020. Anaerobic respiration is the formation of ATP without oxygen. This method still incorporates the respiratory electron transport chain, but without using oxygen as the terminal electron acceptor. Instead, molecules such as sulfate (SO42-), nitrate (NO3?), or sulfur (S) are used as electron acceptors ^ Lollar, Garnet S.; Warr, Oliver; Telling, Jon; Osburn, Magdalena R.; Sherwood Lollar, Barbara (2019). "'Follow the Water': Hydrogeochemical Constraints on Microbial Investigations 2.4 km Below Surface at the Kidd Creek Deep Fluid and Deep Life Observatory". Geomicrobiology Journal. 36: 859?872. doi:10.1080/01490451.2019.1641770. S2CID 199636268. ^ World's Oldest Groundwater Supports Life Through Water-Rock Chemistry Archived 2019-09-10 at the Wayback Machine, July 29, 2019, . ^ Strange life-forms found deep in a mine point to vast 'underground Galapagos' Archived 2019-09-09 at the Wayback Machine, By Corey S. Powell, Sept. 7, 2019, . External links Library resources about Cellular respiration Resources in your library A detailed description of respiration vs. fermentation Kimball's online resource for cellular respiration Cellular Respiration and Fermentation at Clermont College Retrieved from "

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