What Cellular Process Uses Oxygen To Break Food Down, Producing Atp?

Procedure to convert glucose to ATP in cells

Cellular respiration is a prepare of metabolic reactions and processes that take place in the cells of organisms to convert chemical free energy from nutrients into adenosine triphosphate (ATP), then release waste products.^[ane] The reactions involved in respiration are catabolic reactions, which intermission large molecules into smaller ones, releasing free energy. Respiration is ane of the key ways a cell releases chemical free energy to fuel cellular action. 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 free energy from the series of reactions.

Nutrients that are commonly used by beast and plant cells in respiration include sugar, amino acids and fatty acids, and the most common oxidizing agent is molecular oxygen (O_ii). The chemical energy stored in ATP (the bond of its 3rd phosphate group to the rest of the molecule tin can be broken allowing more stable products to course, thereby releasing free energy for utilise by the cell) tin and so be used to drive processes requiring energy, including biosynthesis, locomotion or send of molecules across jail cell membranes.

Aerobic respiration

Aerobic respiration requires oxygen (O₂) in guild 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 bicycle. 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 grouping to grade ATP (adenosine triphosphate), by substrate-level phosphorylation, NADH and FADH_ii

Simplified reaction:	C₆H₁₂O₆ (s) + six O₂ (k) → 6 CO₂ (thou) + 6 H₂O (fifty) + rut
	ΔG = −2880 kJ per mol of C₆H₁₂O₆

The negative ΔG indicates that the reaction can occur spontaneously.

The potential of NADH and FADH₂ is converted to more than ATP through an electron transport chain with oxygen and protons (hydrogen) as the "terminal electron acceptors". Most of the ATP produced past aerobic cellular respiration is made by oxidative phosphorylation. The energy released is used to create a chemiosmotic potential past pumping protons across a membrane. This potential is then used to drive ATP synthase and produce ATP from ADP and a phosphate grouping. Biology textbooks often state that 38 ATP molecules tin be made per oxidized glucose molecule during cellular respiration (2 from glycolysis, 2 from the Krebs cycle, and well-nigh 34 from the electron send system).^[two] Even so, this maximum yield is never quite reached because of losses due to leaky membranes as well as the price of moving pyruvate and ADP into the mitochondrial matrix, and electric current estimates range around 29 to xxx ATP per glucose.^[two]

Aerobic metabolism is up to fifteen times more efficient than anaerobic metabolism (which yields 2 molecules ATP per one molecule glucose). Withal, some anaerobic organisms, such every bit methanogens are able to proceed with anaerobic respiration, yielding more ATP by using inorganic molecules other than oxygen as concluding electron acceptors in the electron transport chain. They share the initial pathway of glycolysis but aerobic metabolism continues with the Krebs bicycle and oxidative phosphorylation. The post-glycolytic reactions have place in the mitochondria in eukaryotic cells, and in the cytoplasm in prokaryotic cells.

Glycolysis

Out of the cytoplasm information technology 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 ship through the electron send chain. The electron transport chain pulls H⁺ ions through the concatenation. From the electron transport concatenation, the released hydrogen ions make ADP for an upshot of 32 ATP. O₂ provides near of the energy for the process and combines with protons and the electrons to brand water. Lastly, ATP leaves through the ATP channel and out of the mitochondria.

Glycolysis is a metabolic pathway that takes place in the cytosol of cells in all living organisms. Glycolysis tin be literally translated as "carbohydrate splitting",^[3] 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 class of 2 net molecules of ATP. Four molecules of ATP per glucose are actually produced, but 2 are consumed every bit part of the preparatory phase. The initial phosphorylation of glucose is required to increase the reactivity (subtract its stability) in order for the molecule to be cleaved into ii pyruvate molecules past the enzyme aldolase. During the pay-off stage of glycolysis, four phosphate groups are transferred to ADP past 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 + two NAD⁺ + 2 P_i + two ADP → 2 pyruvate + 2 H⁺ + 2 NADH + ii ATP + 2 H⁺ + 2 H_twoO + energy

Starting with glucose, i 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 six-phosphate becomes fructose 6-phosphate. An additional ATP is used to phosphorylate fructose vi-phosphate into fructose 1,6-bisphosphate by the assistance of phosphofructokinase. Fructose 1,6-biphosphate then splits into 2 phosphorylated molecules with three carbon chains which later degrades into pyruvate.

Oxidative decarboxylation of pyruvate

Pyruvate is oxidized to acetyl-CoA and CO₂ by the pyruvate dehydrogenase complex (PDC). The PDC contains multiple copies of 3 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

This is likewise chosen the Krebs cycle or the tricarboxylic acid wheel. 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.^[4] When oxygen is present, the mitochondria will undergo aerobic respiration which leads to the Krebs cycle. However, if oxygen is not nowadays, fermentation of the pyruvate molecule will occur. In the presence of oxygen, when acetyl-CoA is produced, the molecule and so enters the citric acid wheel (Krebs bike) inside the mitochondrial matrix, and is oxidized to CO₂ while at the aforementioned fourth dimension reducing NAD to NADH. NADH tin can be used past the electron transport chain to create farther ATP as function of oxidative phosphorylation. To fully oxidize the equivalent of 1 glucose molecule, two acetyl-CoA must be metabolized by the Krebs cycle. Two low-energy waste products, H₂O and CO_two, are created during this cycle.

The citric acid cycle is an 8-step process involving 18 dissimilar enzymes and co-enzymes.^[4] 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 α-ketoglutarate (5 carbons), succinyl-CoA, succinate, fumarate, malate, and, finally, oxaloacetate.

The net proceeds from ane cycle is 3 NADH and one FADH₂ every bit hydrogen- (proton plus electron)-carrying compounds and 1 high-free energy GTP, which may subsequently be used to produce ATP. Thus, the total yield from 1 glucose molecule (2 pyruvate molecules) is half dozen NADH, 2 FADH₂, and two ATP.

Oxidative phosphorylation

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 electrons are finally transferred to exogenous oxygen and, with the add-on 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 send concatenation and used for oxidative phosphorylation.

Pace	coenzyme yield	ATP yield	Source of ATP
Glycolysis preparatory phase		−2	Phosphorylation of glucose and fructose half-dozen-phosphate uses two ATP from the cytoplasm.
Glycolysis pay-off phase		4	Substrate-level phosphorylation
Glycolysis pay-off phase	2 NADH	3 or 5	Oxidative phosphorylation : Each NADH produces internet 1.five ATP (instead of usual 2.v) due to NADH transport over the mitochondrial membrane
Oxidative decarboxylation of pyruvate	2 NADH	five	Oxidative phosphorylation
Krebs bicycle		2	Substrate-level phosphorylation
	6 NADH	15	Oxidative phosphorylation
	2 FADH_two	iii	Oxidative phosphorylation
Full yield		xxx or 32 ATP	From the consummate 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 more often than not 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 employ the stored energy in the proton electrochemical gradient.

Pyruvate is taken upwardly past a specific, low K _m 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 (H_twoPO_iv ⁻; P_i) 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 (too called adenine nucleotide translocase, ANT) is an antiporter and exchanges ADP and ATP across the inner membrane. The driving strength is due to the ATP (−4) having a more negative accuse than the ADP (−iii), and thus it dissipates some of the electrical component of the proton electrochemical gradient.

The outcome of these ship processes using the proton electrochemical gradient is that more than than iii H⁺ are needed to make 1 ATP. Apparently, this reduces the theoretical efficiency of the whole procedure and the likely maximum is closer to 28–30 ATP molecules.^[2] In practice the efficiency may be even lower because the inner membrane of the mitochondria is slightly leaky to protons.^[5] Other factors may too dissipate the proton slope creating an manifestly leaky mitochondria. An uncoupling protein known every bit thermogenin is expressed in some jail cell types and is a aqueduct that can transport protons. When this protein is active in the inner membrane information technology short circuits the coupling between the electron transport chain and ATP synthesis. The potential free energy from the proton gradient is non used to brand ATP but generates heat. This is particularly of import in brown fat thermogenesis of newborn and hibernating mammals.

According to some newer sources, the ATP yield during aerobic respiration is not 36–38, merely only about 30–32 ATP molecules / 1 molecule of glucose ^[six], because:

ATP : NADH+H⁺ and ATP : FADH_ii ratios during the oxidative phosphorylation appear to be not 3 and ii, but 2.v and one.5 respectively. Unlike in the substrate-level phosphorylation, the stoichiometry here is difficult to establish.
- ATP synthase produces one ATP / 3 H⁺. Yet 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⁺ / one 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 + four) or 6 H⁺ / 1 FADH_two (two + 4).

And then the terminal stoichiometry is

ane NADH+H⁺ : ten H⁺ : 10/4 ATP = 1 NADH+H⁺ : 2.five ATP

i FADH₂ : 6 H⁺ : six/4 ATP = i FADH_two : ane.5 ATP

ATP : NADH+H⁺ coming from glycolysis ratio during the oxidative phosphorylation is
- ane.5, equally 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.v 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: two ATP from glycolysis + 2 ATP (directly GTP) from Krebs wheel
Oxidative phosphorylation
- two NADH+H⁺ from glycolysis: ii × 1.five ATP (if glycerol phosphate shuttle transfers hydrogen atoms) or 2 × 2.5 ATP (malate-aspartate shuttle)
- 2 NADH+H⁺ from the oxidative decarboxylation of pyruvate and vi from Krebs bike: 8 × ii.5 ATP
- ii FADH_ii from the Krebs cycle: 2 × one.5 ATP

Altogether this gives four + iii (or v) + 20 + three = 30 (or 32) ATP per molecule of glucose

These figures may even so crave further tweaking as new structural details go bachelor. The above value of 3 H+/ATP for the synthase assumes that the synthase translocates ix 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 at present known that this is 10 in yeast Fo^[seven] and 8 for vertebrates.^[eight] Including one H⁺ for the send reactions, this ways that synthesis of i ATP requires one+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 contempo review.^[9]

The total ATP yield in ethanol or lactic acid fermentation is only 2 molecules coming from glycolysis, because pyruvate is non transferred to the mitochondrion and finally oxidized to the carbon dioxide (CO₂), but reduced to ethanol or lactic acrid in the cytoplasm.^[vi]

Fermentation

Without oxygen, pyruvate (pyruvic acid) is non 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 and then that they can perform glycolysis once again and removing the excess pyruvate. Fermentation oxidizes NADH to NAD⁺ then 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 chosen lactic acrid fermentation. In strenuous practice, 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 grade lactate. Lactate germination is catalyzed by lactate dehydrogenase in a reversible reaction. Lactate can also be used as an indirect forerunner for liver glycogen. During recovery, when oxygen becomes available, NAD⁺ attaches to hydrogen from lactate to course ATP. In yeast, the waste matter products are ethanol and carbon dioxide. This type of fermentation is known every bit alcoholic or ethanol fermentation. The ATP generated in this process is made past substrate-level phosphorylation, which does not require oxygen.

Fermentation is less efficient at using the energy from glucose: but 2 ATP are produced per glucose, compared to the 38 ATP per glucose nominally produced by aerobic respiration. Glycolytic ATP, nevertheless, is created more rapidly. For prokaryotes to continue a rapid growth charge per unit when they are shifted from an aerobic surround to an anaerobic environment, they must increase the charge per unit of the glycolytic reactions. For multicellular organisms, during curt bursts of strenuous action, muscle cells use fermentation to supplement the ATP production from the slower aerobic respiration, so fermentation may be used by a prison cell even earlier the oxygen levels are depleted, as is the case in sports that practice not crave athletes to pace themselves, such as sprinting.

Anaerobic respiration

Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such equally oxygen to produce large amounts of free energy, to bulldoze the bulk product of ATP.

Anaerobic respiration is used by some microorganisms in which neither oxygen (aerobic respiration) nor pyruvate derivatives (fermentation) is the final electron acceptor. Rather, an inorganic acceptor such as sulfate (SO₄ ^2-), nitrate (NO_iii ^–), or sulfur (S) is used.^[10] 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 alive 7900 anxiety below the surface, and which breathe sulfur in order to survive. These organisms are also remarkable due to consuming minerals such as pyrite equally their food source.^[eleven] ^[12] ^[13]

References

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^ Reece1 Urry2 Cain3 Wasserman4 Minorsky5 Jackson6, Jane1 Lisa2 Michael3 Steven4 Peter5 Robert6 (2010). Campbell Biological science 9th Edition. Pearson Didactics, Inc. p. 168.
^ ^a ^b "Cellular Respiration" (PDF). Archived (PDF) from the original on 2017-05-10.
^ Porter, R.; Brand, G. (1 September 1995). "Mitochondrial proton conductance and H+/O ratio are independent of electron ship rate in isolated hepatocytes". The Biochemical Periodical (Free full text). 310 (Pt 2): 379–382. doi:10.1042/bj3100379. ISSN 0264-6021. PMC1135905. PMID 7654171.
^ ^a ^b ^c Stryer, Lubert (1995). Biochemistry (4th ed.). New York – Basingstoke: Westward. H. Freeman and Company. ISBN978-0716720096.
^ Stock D, Leslie AG, Walker JE (1999). "Molecular compages of the rotary motor in ATP synthase". Science. 286 (5445): 1700–5. doi:10.1126/science.286.5445.1700. PMID 10576729. {{cite journal}}: CS1 maint: uses authors parameter (link)
^ Watt, I.N., Montgomery, M.Thou., 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. U.s.a.. 107 (39): 16823–16827. doi:x.1073/pnas.1011099107. PMC2947889. PMID 20847295. {{cite journal}}: 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.lumenlearning.org. Dizzying.com. Retrieved November 19, 2020. Anaerobic respiration is the formation of ATP without oxygen. This method all the same incorporates the respiratory electron transport chain, just without using oxygen as the terminal electron acceptor. Instead, molecules such every bit 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 H2o': Hydrogeochemical Constraints on Microbial Investigations ii.4 km Below Surface at the Kidd Creek Deep Fluid and Deep Life Observatory". Geomicrobiology Journal. 36: 859–872. doi:ten.1080/01490451.2019.1641770. S2CID 199636268.
^ Globe's Oldest Groundwater Supports Life Through H2o-Stone Chemistry Archived 2019-09-x at the Wayback Motorcar, July 29, 2019, deepcarbon.net.
^ Strange life-forms institute deep in a mine point to vast 'undercover Galapagos' Archived 2019-09-09 at the Wayback Machine, By Corey Due south. Powell, Sept. 7, 2019, nbcnews.com.