Explain How Molecules Other Than Glucose Can Be Used as Energy Sources.

Identify the reactants and products of cellular respiration and where these reactions occur in a cell

Now that we've learned how autotrophs like plants convert sunlight to sugars, let's take a look at how all eukaryotes—which includes humans!—make use of those sugars.

In the process of photosynthesis, plants and other photosynthetic producers create glucose, which stores free energy in its chemical bonds. Then, both plants and consumers, such as animals, undergo a serial of metabolic pathways—collectively chosen cellular respiration. Cellular respiration extracts the free energy from the bonds in glucose and converts it into a form that all living things can use.

Learning Objectives

• Describe the process of glycolysis and identify its reactants and products
• Draw the process of pyruvate oxidation and identify its reactants and products
• Depict the process of the citric acid cycle (Krebs cycle) and place its reactants and products
• Describe the respiratory chain (electron ship chain) and its role in cellular respiration

Cellular respiration is a process that all living things use to convert glucose into energy. Autotrophs (like plants) produce glucose during photosynthesis. Heterotrophs (like humans) ingest other living things to obtain glucose. While the process tin can seem complex, this page takes yous through the key elements of each role of cellular respiration.

Glycolysis

Glycolysis is the outset step in the breakdown of glucose to extract energy for cellular metabolism. Nearly all living organisms carry out glycolysis as part of their metabolism. The process does non use oxygen and is therefore anaerobic (processes that employ oxygen are chosen aerobic). Glycolysis takes identify in the cytoplasm of both prokaryotic and eukaryotic cells. Glucose enters heterotrophic cells in two ways.

1. Through secondary active transport in which the transport takes place against the glucose concentration gradient.
2. Through a group of integral proteins called GLUT proteins, also known every bit glucose transporter proteins. These transporters assist in the facilitated diffusion of glucose.

Glycolysis begins with the six carbon band-shaped structure of a unmarried glucose molecule and ends with 2 molecules of a three-carbon sugar calledpyruvate(Effigy 1).

Figure one. Reactants and products of glycolysis.

Glycolysis consists of 10 steps divided into 2 distinct halves. The starting time half of the glycolysis is likewise known as the free energy-requiring steps. This pathway traps the glucose molecule in the cell and uses energy to modify information technology so that the six-carbon saccharide molecule can be divide evenly into the two three-carbon molecules. The second one-half of glycolysis (likewise known equally the energy-releasing steps) extracts energy from the molecules and stores it in the form of ATP and NADH, the reduced grade of NAD.

Outset One-half of Glycolysis (Free energy-Requiring Steps)

Figure 2. The first half of glycolysis uses two ATP molecules in the phosphorylation of glucose, which is then split into two 3-carbon molecules.

Step 1. The first step in glycolysis is catalyzed by hexokinase, an enzyme with broad specificity that catalyzes the phosphorylation of six-carbon sugars. Hexokinase phosphorylates glucose using ATP every bit the source of the phosphate, producing glucose-six-phosphate, a more reactive form of glucose. This reaction prevents the phosphorylated glucose molecule from standing to interact with the Overabundance proteins, and it can no longer leave the cell because the negatively charged phosphate volition not allow it to cantankerous the hydrophobic interior of the plasma membrane.

Footstep two. In the second step of glycolysis, an isomerase converts glucose-six-phosphate into one of its isomers, fructose-6-phosphate. Anisomerase is an enzyme that catalyzes the conversion of a molecule into one of its isomers. This alter from phosphoglucose to phosphofructose allows the eventual split of the sugar into two 3-carbon molecules.

Step 3. The 3rd step is the phosphorylation of fructose-6-phosphate, catalyzed by the enzyme phosphofructokinase. A second ATP molecule donates a high-energy phosphate to fructose-half-dozen-phosphate, producing fructose-one,6-bisphosphate. In this pathway, phosphofructokinase is a rate-limiting enzyme. It is active when the concentration of ADP is high; it is less active when ADP levels are depression and the concentration of ATP is high. Thus, if at that place is "sufficient" ATP in the system, the pathway slows down. This is a blazon of end production inhibition, since ATP is the end product of glucose catabolism.

Stride 4. The newly added high-free energy phosphates further destabilize fructose-i,six-bisphosphate. The fourth pace in glycolysis employs an enzyme, aldolase, to carve 1,vi-bisphosphate into two 3-carbon isomers: dihydroxyacetone-phosphate and glyceraldehyde-3-phosphate.

Footstep 5. In the 5th footstep, an isomerase transforms the dihydroxyacetone-phosphate into its isomer, glyceraldehyde-3-phosphate. Thus, the pathway will go along with two molecules of a single isomer. At this indicate in the pathway, there is a net investment of energy from two ATP molecules in the breakdown of one glucose molecule.

Second One-half of Glycolysis (Energy-Releasing Steps)

So far, glycolysis has toll the jail cell 2 ATP molecules and produced ii modest, 3-carbon sugar molecules. Both of these molecules volition proceed through the second one-half of the pathway, and sufficient free energy will be extracted to pay dorsum the two ATP molecules used as an initial investment and produce a profit for the cell of 2 boosted ATP molecules and two even higher-free energy NADH molecules.

Figure iii. The second one-half of glycolysis involves phosphorylation without ATP investment (step 6) and produces two NADH and four ATP molecules per glucose.

Step 6. The sixth step in glycolysis (Figure 3) oxidizes the carbohydrate (glyceraldehyde-3-phosphate), extracting high-energy electrons, which are picked up by the electron carrier NAD⁺, producing NADH. The carbohydrate is then phosphorylated by the addition of a second phosphate group, producing 1,3-bisphosphoglycerate. Annotation that the 2nd phosphate grouping does non crave another ATP molecule.

Hither again is a potential limiting factor for this pathway. The continuation of the reaction depends upon the availability of the oxidized class of the electron carrier, NAD⁺. Thus, NADH must be continuously oxidized back into NAD⁺ in order to proceed this step going. If NAD⁺ is not bachelor, the second one-half of glycolysis slows down or stops. If oxygen is available in the system, the NADH will be oxidized readily, though indirectly, and the high-energy electrons from the hydrogen released in this process will be used to produce ATP. In an surround without oxygen, an alternate pathway (fermentation) tin provide the oxidation of NADH to NAD⁺.

Step 7. In the seventh step, catalyzed past phosphoglycerate kinase (an enzyme named for the reverse reaction), ane,3-bisphosphoglycerate donates a high-energy phosphate to ADP, forming ane molecule of ATP. (This is an instance of substrate-level phosphorylation.) A carbonyl group on the i,3-bisphosphoglycerate is oxidized to a carboxyl group, and 3-phosphoglycerate is formed.

Pace 8. In the eighth step, the remaining phosphate group in 3-phosphoglycerate moves from the third carbon to the second carbon, producing 2-phosphoglycerate (an isomer of 3-phosphoglycerate). The enzyme catalyzing this step is a mutase (a blazon of isomerase).

Step nine. Enolase catalyzes the 9th step. This enzyme causes ii-phosphoglycerate to lose h2o from its structure; this is a dehydration reaction, resulting in the germination of a double bond that increases the potential free energy in the remaining phosphate bond and produces phosphoenolpyruvate (PEP).

Step ten. The final step in glycolysis is catalyzed by the enzyme pyruvate kinase (the enzyme in this case is named for the reverse reaction of pyruvate'south conversion into PEP) and results in the product of a second ATP molecule by substrate-level phosphorylation and the compound pyruvic acid (or its salt form, pyruvate). Many enzymes in enzymatic pathways are named for the reverse reactions, since the enzyme can catalyze both frontward and reverse reactions.

Outcomes of Glycolysis

Glycolysis starts with glucose and ends with two pyruvate molecules, a full of four ATP molecules and 2 molecules of NADH. Two ATP molecules were used in the first one-half of the pathway to prepare the vi-carbon ring for cleavage, so the cell has a cyberspace gain of ii ATP molecules and two NADH molecules for its utilize.

If the cell cannot catabolize the pyruvate molecules further, information technology will harvest just two ATP molecules from 1 molecule of glucose. Mature mammalian red blood cells are not capable ofaerobic respiration—the process in which organisms convert energy in the presence of oxygen—and glycolysis is their sole source of ATP. If glycolysis is interrupted, these cells lose their ability to maintain their sodium-potassium pumps, and eventually, they die.

The concluding pace in glycolysis will not occur if pyruvate kinase, the enzyme that catalyzes the formation of pyruvate, is not available in sufficient quantities. In this situation, the entire glycolysis pathway will proceed, just only two ATP molecules volition be fabricated in the second half. Thus, pyruvate kinase is a charge per unit-limiting enzyme for glycolysis.

In Summary: Glycolysis

Glycolysis is the first pathway used in the breakdown of glucose to extract energy. Information technology was probably 1 of the primeval metabolic pathways to evolve and is used past about all of the organisms on world. Glycolysis consists of 2 parts: The first part prepares the 6-carbon ring of glucose for cleavage into two three-carbon sugars. ATP is invested in the process during this one-half to energize the separation. The second half of glycolysis extracts ATP and loftier-energy electrons from hydrogen atoms and attaches them to NAD⁺. Two ATP molecules are invested in the showtime half and four ATP molecules are formed by substrate phosphorylation during the 2d half. This produces a net gain of two ATP and two NADH molecules for the cell.

Figure 4 shows the entire process of glycolysis in one epitome:

Figure four. Glycolysis

Pyruvate Oxidation

If oxygen is bachelor, aerobic respiration will go forrad. In eukaryotic cells, the pyruvate molecules produced at the end of glycolysis are transported into mitochondria, which are the sites of cellular respiration. At that place, pyruvate volition be transformed into an acetyl group that will be picked up and activated by a carrier compound called coenzyme A (CoA). The resulting compound is called acetyl CoA. CoA is fabricated from vitamin B5, pantothenic acid. Acetyl CoA can exist used in a variety of ways by the cell, but its major function is to deliver the acetyl group derived from pyruvate to the adjacent stage of the pathway in glucose catabolism.

Breakdown of Pyruvate

In order for pyruvate (which is the product of glycolysis) to enter the Citric Acid Bicycle (the next pathway in cellular respiration), it must undergo several changes. The conversion is a three-step procedure (Figure 5).

Figure v. Upon inbound the mitochondrial matrix, a multi-enzyme complex converts pyruvate into acetyl CoA. In the process, carbon dioxide is released and one molecule of NADH is formed.

Step i. A carboxyl group is removed from pyruvate, releasing a molecule of carbon dioxide into the surrounding medium. The result of this step is a two-carbon hydroxyethyl group bound to the enzyme (pyruvate dehydrogenase). This is the start of the six carbons from the original glucose molecule to be removed. This step proceeds twice (remember: at that place are two pyruvate molecules produced at the end of glycolysis) for every molecule of glucose metabolized; thus, two of the six carbons will take been removed at the finish of both steps.

Step ii. NAD⁺ is reduced to NADH. The hydroxyethyl group is oxidized to an acetyl group, and the electrons are picked up by NAD⁺, forming NADH. The loftier-energy electrons from NADH will exist used after to generate ATP.

Step three. An acetyl group is transferred to conenzyme A, resulting in acetyl CoA. The enzyme-bound acetyl group is transferred to CoA, producing a molecule of acetyl CoA.

Notation that during the second stage of glucose metabolism, whenever a carbon cantlet is removed, it is bound to 2 oxygen atoms, producing carbon dioxide, one of the major stop products of cellular respiration.

Acetyl CoA to CO₂

In the presence of oxygen, acetyl CoA delivers its acetyl group to a four-carbon molecule, oxaloacetate, to form citrate, a six-carbon molecule with 3 carboxyl groups; this pathway will harvest the remainder of the extractable energy from what began as a glucose molecule. This single pathway is chosen by different names, but nosotros volition primarily call information technology the Citric Acrid Bicycle.

In Summary: Pyruvate Oxidation

In the presence of oxygen, pyruvate is transformed into an acetyl group attached to a carrier molecule of coenzyme A. The resulting acetyl CoA can enter several pathways, but most ofttimes, the acetyl group is delivered to the citric acrid cycle for further catabolism. During the conversion of pyruvate into the acetyl grouping, a molecule of carbon dioxide and ii high-free energy electrons are removed. The carbon dioxide accounts for two (conversion of two pyruvate molecules) of the 6 carbons of the original glucose molecule. The electrons are picked upwards past NAD⁺, and the NADH carries the electrons to a later pathway for ATP production. At this bespeak, the glucose molecule that originally entered cellular respiration has been completely oxidized. Chemic potential energy stored within the glucose molecule has been transferred to electron carriers or has been used to synthesize a few ATPs.

Citric Acrid Cycle

Like the conversion of pyruvate to acetyl CoA, the citric acid cycle takes identify in the matrix of mitochondria.This single pathway is called past different names: the citric acid cycle (for the commencement intermediate formed—citric acid, or citrate—when acetate joins to the oxaloacetate), the TCA bicycle (since citric acid or citrate and isocitrate are tricarboxylic acids), and the Krebs cycle, later on Hans Krebs, who first identified the steps in the pathway in the 1930s in dove flying muscles.

Well-nigh all of the enzymes of the citric acid cycle are soluble, with the single exception of the enzyme succinate dehydrogenase, which is embedded in the inner membrane of the mitochondrion. Dissimilar glycolysis, the citric acid cycle is a closed loop: The last part of the pathway regenerates the chemical compound used in the first step. The eight steps of the bicycle are a series of redox, dehydration, hydration, and decarboxylation reactions that produce two carbon dioxide molecules, one GTP/ATP, and reduced forms of NADH and FADH₂ (Figure 6). This is considered an aerobic pathway because the NADH and FADH₂ produced must transfer their electrons to the next pathway in the system, which will use oxygen. If this transfer does not occur, the oxidation steps of the citric acid cycle likewise do not occur. Note that the citric acrid cycle produces very picayune ATP directly and does non directly consume oxygen.

Figure 6. In the citric acid cycle, the acetyl group from acetyl CoA is attached to a four-carbon oxaloacetate molecule to class a six-carbon citrate molecule. Through a series of steps, citrate is oxidized, releasing 2 carbon dioxide molecules for each acetyl group fed into the cycle. In the procedure, three NAD⁺ molecules are reduced to NADH, one FAD molecule is reduced to FADH_ii, and ane ATP or GTP (depending on the cell type) is produced (by substrate-level phosphorylation). Considering the last production of the citric acrid wheel is besides the start reactant, the cycle runs continuously in the presence of sufficient reactants. (credit: modification of piece of work by "Yikrazuul"/Wikimedia Commons)

Steps in the Citric Acid Cycle

Pace 1. Prior to the get-go of the first step, pyruvate oxidation must occur. So, the first step of the cycle begins: This is a condensation step, combining the ii-carbon acetyl group with a four-carbon oxaloacetate molecule to course a half dozen-carbon molecule of citrate. CoA is spring to a sulfhydryl group (-SH) and diffuses away to eventually combine with another acetyl group. This step is irreversible because it is highly exergonic. The rate of this reaction is controlled by negative feedback and the amount of ATP available. If ATP levels increase, the rate of this reaction decreases. If ATP is in brusk supply, the rate increases.

Step ii. In step two, citrate loses ane water molecule and gains another every bit citrate is converted into its isomer, isocitrate.

Step 3. In step iii, isocitrate is oxidized, producing a five-carbon molecule, α-ketoglutarate, together with a molecule of CO₂ and 2 electrons, which reduce NAD⁺ to NADH. This pace is also regulated past negative feedback from ATP and NADH, and a positive outcome of ADP.

Steps 3 and four. Steps 3 and 4 are both oxidation and decarboxylation steps, which release electrons that reduce NAD⁺ to NADH and release carboxyl groups that form CO₂ molecules. α-Ketoglutarate is the production of step 3, and a succinyl group is the production of footstep four. CoA binds the succinyl group to form succinyl CoA. The enzyme that catalyzes step four is regulated by feedback inhibition of ATP, succinyl CoA, and NADH.

Stride five. In stride five, a phosphate group is substituted for coenzyme A, and a high-energy bond is formed. This energy is used in substrate-level phosphorylation (during the conversion of the succinyl group to succinate) to form either guanine triphosphate (GTP) or ATP. In that location are two forms of the enzyme, called isoenzymes, for this pace, depending upon the blazon of animal tissue in which they are found. One form is found in tissues that use large amounts of ATP, such as centre and skeletal muscle. This form produces ATP. The second form of the enzyme is institute in tissues that have a high number of anabolic pathways, such as liver. This form produces GTP. GTP is energetically equivalent to ATP; however, its use is more restricted. In particular, poly peptide synthesis primarily uses GTP.

Pace vi. Step six is a aridity process that converts succinate into fumarate. Two hydrogen atoms are transferred to FAD, producing FADH₂. The energy contained in the electrons of these atoms is bereft to reduce NAD⁺ simply acceptable to reduce FAD. Unlike NADH, this carrier remains attached to the enzyme and transfers the electrons to the electron send chain straight. This procedure is fabricated possible past the localization of the enzyme catalyzing this step inside the inner membrane of the mitochondrion.

Footstep 7. H2o is added to fumarate during footstep seven, and malate is produced. The concluding step in the citric acid cycle regenerates oxaloacetate past oxidizing malate. Some other molecule of NADH is produced in the process.

Products of the Citric Acrid Cycle

Ii carbon atoms come into the citric acid bike from each acetyl group, representing 4 out of the 6 carbons of 1 glucose molecule. Two carbon dioxide molecules are released on each plow of the cycle; however, these do non necessarily incorporate the most recently added carbon atoms. The two acetyl carbon atoms will eventually be released on later turns of the bike; thus, all six carbon atoms from the original glucose molecule are somewhen incorporated into carbon dioxide. Each turn of the wheel forms three NADH molecules and one FADH_ii molecule. These carriers will connect with the concluding portion of aerobic respiration to produce ATP molecules. 1 GTP or ATP is also made in each cycle. Several of the intermediate compounds in the citric acrid cycle can be used in synthesizing not-essential amino acids; therefore, the wheel is amphibolic (both catabolic and anabolic).

In Summary: Citric Acid Cycle

The citric acid bike is a series of redox and decarboxylation reactions that remove high-energy electrons and carbon dioxide. The electrons temporarily stored in molecules of NADH and FADH_two are used to generate ATP in a subsequent pathway. 1 molecule of either GTP or ATP is produced by substrate-level phosphorylation on each turn of the cycle. There is no comparison of the cyclic pathway with a linear one.

Electron Transport Chain

Y'all have but read almost ii pathways in cellular respiration—glycolysis and the citric acid bike—that generate ATP. However, virtually of the ATP generated during the aerobic catabolism of glucose is not generated straight from these pathways. Rather, it is derived from a process that begins with moving electrons through a series of electron transporters that undergo redox reactions: the electron transport chain. This causes hydrogen ions to accrue within the matrix space. Therefore, a concentration slope forms in which hydrogen ions diffuse out of the matrix space by passing through ATP synthase. The current of hydrogen ions powers the catalytic activity of ATP synthase, which phosphorylates ADP, producing ATP.

Electron Transport Chain

Effigy seven. The electron transport chain is a series of electron transporters embedded in the inner mitochondrial membrane that shuttles electrons from NADH and FADH_two to molecular oxygen. In the procedure, protons are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water.

The electron send chain (Figure 7) is the last component of aerobic respiration and is the only part of glucose metabolism that uses atmospheric oxygen. Oxygen continuously diffuses into plants; in animals, information technology enters the body through the respiratory system. Electron send is a serial of redox reactions that resemble a relay race or bucket brigade in that electrons are passed speedily from ane component to the next, to the endpoint of the chain where the electrons reduce molecular oxygen, producing water. There are iv complexes composed of proteins, labeled I through IV in Figure seven, and the assemblage of these four complexes, together with associated mobile, accessory electron carriers, is chosen the electron transport chain. The electron ship chain is nowadays in multiple copies in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes. Notation, notwithstanding, that the electron transport chain of prokaryotes may not crave oxygen as some live in anaerobic weather condition. The common feature of all electron ship bondage is the presence of a proton pump to create a proton gradient beyond a membrane.

Complex I

To outset, ii electrons are carried to the kickoff complex aboard NADH. This complex, labeled I, is composed of flavin mononucleotide (FMN) and an iron-sulfur (Atomic number 26-S)-containing poly peptide. FMN, which is derived from vitamin B₂, also called riboflavin, is one of several prosthetic groups or co-factors in the electron transport chain. Aprosthetic group is a non-protein molecule required for the activeness of a protein. Prosthetic groups are organic or inorganic, non-peptide molecules bound to a protein that facilitate its function; prosthetic groups include co-enzymes, which are the prosthetic groups of enzymes. The enzyme in circuitous I is NADH dehydrogenase and is a very large protein, containing 45 amino acid chains. Complex I can pump four hydrogen ions beyond the membrane from the matrix into the intermembrane space, and information technology is in this mode that the hydrogen ion slope is established and maintained between the two compartments separated past the inner mitochondrial membrane.

Q and Complex II

Complex Two directly receives FADH_two, which does not pass through complex I. The compound connecting the first and second complexes to the third isubiquinone (Q). The Q molecule is lipid soluble and freely moves through the hydrophobic cadre of the membrane. In one case information technology is reduced, (QH₂), ubiquinone delivers its electrons to the next complex in the electron ship chain. Q receives the electrons derived from NADH from complex I and the electrons derived from FADH₂ from circuitous Ii, including succinate dehydrogenase. This enzyme and FADH_two grade a small complex that delivers electrons directly to the electron transport chain, bypassing the first complex. Since these electrons bypass and thus exercise non energize the proton pump in the kickoff complex, fewer ATP molecules are made from the FADH₂ electrons. The number of ATP molecules ultimately obtained is directly proportional to the number of protons pumped across the inner mitochondrial membrane.

Complex 3

The third complex is equanimous of cytochrome b, another Fe-S protein, Rieske centre (2Fe-2S center), and cytochrome c proteins; this complex is also called cytochrome oxidoreductase. Cytochrome proteins have a prosthetic group of heme. The heme molecule is similar to the heme in hemoglobin, but information technology carries electrons, non oxygen. Every bit a consequence, the fe ion at its core is reduced and oxidized as information technology passes the electrons, fluctuating betwixt unlike oxidation states: Fe^{+ +} (reduced) and Fe^{+ + +} (oxidized). The heme molecules in the cytochromes take slightly different characteristics due to the furnishings of the unlike proteins bounden them, giving slightly different characteristics to each complex. Complex III pumps protons through the membrane and passes its electrons to cytochrome c for transport to the 4th complex of proteins and enzymes (cytochrome c is the acceptor of electrons from Q; however, whereas Q carries pairs of electrons, cytochrome c can accept but one at a time).

Circuitous Iv

The 4th complex is composed of cytochrome proteins c, a, and a₃. This complex contains two heme groups (1 in each of the ii cytochromes, a, and a₃) and 3 copper ions (a pair of Cu_A and one Cu_B in cytochrome a_iii). The cytochromes hold an oxygen molecule very tightly betwixt the iron and copper ions until the oxygen is completely reduced. The reduced oxygen so picks up 2 hydrogen ions from the surrounding medium to make water (H_twoO). The removal of the hydrogen ions from the system contributes to the ion gradient used in the process of chemiosmosis.

Chemiosmosis

In chemiosmosis, the free free energy from the series of redox reactions but described is used to pump hydrogen ions (protons) across the membrane. The uneven distribution of H⁺ ions beyond the membrane establishes both concentration and electrical gradients (thus, an electrochemical gradient), owing to the hydrogen ions' positive charge and their aggregation on one side of the membrane.

If the membrane were open to diffusion by the hydrogen ions, the ions would tend to diffuse back across into the matrix, driven by their electrochemical gradient. Recall that many ions cannot diffuse through the nonpolar regions of phospholipid membranes without the assist of ion channels. Similarly, hydrogen ions in the matrix space can only pass through the inner mitochondrial membrane through an integral membrane protein called ATP synthase (Effigy viii). This complex protein acts as a tiny generator, turned by the force of the hydrogen ions diffusing through information technology, down their electrochemical gradient. The turning of parts of this molecular machine facilitates the addition of a phosphate to ADP, forming ATP, using the potential energy of the hydrogen ion gradient.

Do Question

Effigy viii. ATP synthase is a circuitous, molecular auto that uses a proton (H⁺) gradient to course ATP from ADP and inorganic phosphate (Pi). (Credit: modification of work by Klaus Hoffmeier)

Dinitrophenol (DNP) is an uncoupler that makes the inner mitochondrial membrane leaky to protons. It was used until 1938 as a weight-loss drug. What issue would you lot expect DNP to have on the change in pH across the inner mitochondrial membrane? Why exercise you recall this might exist an constructive weight-loss drug?

Bear witness Respond

Afterward DNP poisoning, the electron send chain can no longer form a proton slope, and ATP synthase can no longer brand ATP. DNP is an effective diet drug because information technology uncouples ATP synthesis; in other words, subsequently taking it, a person obtains less energy out of the food he or she eats. Interestingly, ane of the worst side effects of this drug is hyperthermia, or overheating of the trunk. Since ATP cannot be formed, the energy from electron transport is lost equally heat.

Chemiosmosis (Figure 9) is used to generate xc percent of the ATP made during aerobic glucose catabolism; information technology is besides the method used in the light reactions of photosynthesis to harness the free energy of sunlight in the process of photophosphorylation. Call back that the product of ATP using the process of chemiosmosis in mitochondria is called oxidative phosphorylation. The overall result of these reactions is the production of ATP from the energy of the electrons removed from hydrogen atoms. These atoms were originally office of a glucose molecule. At the cease of the pathway, the electrons are used to reduce an oxygen molecule to oxygen ions. The extra electrons on the oxygen attract hydrogen ions (protons) from the surrounding medium, and water is formed.

Practice Question

Figure 9. In oxidative phosphorylation, the pH gradient formed by the electron transport concatenation is used past ATP synthase to grade ATP.

Cyanide inhibits cytochrome c oxidase, a component of the electron transport chain. If cyanide poisoning occurs, would you expect the pH of the intermembrane infinite to increase or decrease? What effect would cyanide take on ATP synthesis?

Evidence Reply

Afterward cyanide poisoning, the electron transport chain tin can no longer pump electrons into the intermembrane space. The pH of the intermembrane space would increase, the pH gradient would decrease, and ATP synthesis would stop.

ATP Yield

The number of ATP molecules generated from the catabolism of glucose varies. For case, the number of hydrogen ions that the electron send chain complexes can pump through the membrane varies between species. Some other source of variance stems from the shuttle of electrons across the membranes of the mitochondria. (The NADH generated from glycolysis cannot easily enter mitochondria.) Thus, electrons are picked up on the inside of mitochondria by either NAD⁺ or FAD⁺. As you have learned before, these FAD⁺ molecules can transport fewer ions; consequently, fewer ATP molecules are generated when FAD⁺ acts every bit a carrier. NAD⁺ is used as the electron transporter in the liver and FAD⁺ acts in the encephalon.

Another factor that affects the yield of ATP molecules generated from glucose is the fact that intermediate compounds in these pathways are used for other purposes. Glucose catabolism connects with the pathways that build or break down all other biochemical compounds in cells, and the result is somewhat messier than the ideal situations described thus far. For example, sugars other than glucose are fed into the glycolytic pathway for free energy extraction. Moreover, the v-carbon sugars that grade nucleic acids are made from intermediates in glycolysis. Sure nonessential amino acids can be fabricated from intermediates of both glycolysis and the citric acid cycle. Lipids, such as cholesterol and triglycerides, are besides made from intermediates in these pathways, and both amino acids and triglycerides are broken downwards for energy through these pathways. Overall, in living systems, these pathways of glucose catabolism excerpt about 34 percent of the energy contained in glucose.

In Summary: Electron Transport Chain

The electron ship chain is the portion of aerobic respiration that uses gratis oxygen as the last electron acceptor of the electrons removed from the intermediate compounds in glucose catabolism. The electron transport concatenation is equanimous of four large, multiprotein complexes embedded in the inner mitochondrial membrane and two small diffusible electron carriers shuttling electrons between them. The electrons are passed through a series of redox reactions, with a minor amount of free energy used at 3 points to transport hydrogen ions beyond a membrane. This process contributes to the gradient used in chemiosmosis. The electrons passing through the electron transport concatenation gradually lose energy, High-energy electrons donated to the concatenation past either NADH or FADH₂ complete the chain, as low-energy electrons reduce oxygen molecules and form water. The level of gratis energy of the electrons drops from about 60 kcal/mol in NADH or 45 kcal/mol in FADH_ii to about 0 kcal/mol in water. The end products of the electron transport chain are water and ATP. A number of intermediate compounds of the citric acid bike tin can be diverted into the anabolism of other biochemical molecules, such as nonessential amino acids, sugars, and lipids. These aforementioned molecules can serve equally energy sources for the glucose pathways.

Let'south Review

Cellular respiration is a collection of three unique metabolic pathways: glycolysis, the citric acid cycle, and the electron transport chain. Glycolysis is an anaerobic process, while the other ii pathways are aerobic. In guild to move from glycolysis to the citric acid cycle, pyruvate molecules (the output of glycolysis) must exist oxidized in a procedure called pyruvate oxidation.

Glycolysis

Glycolysis is the first pathway in cellular respiration. This pathway is anaerobic and takes identify in the cytoplasm of the cell. This pathway breaks downward ane glucose molecule and produces 2 pyruvate molecules. There are ii halves of glycolysis, with five steps in each half. The outset half is known as the "energy requiring" steps. This half splits glucose, and uses up 2 ATP. If the concentration of pyruvate kinase is high enough, the 2d half of glycolysis tin can continue. In the 2nd one-half, the "free energy releasing: steps, iv molecules of ATP and 2 NADH are released. Glycolysis has a net gainof 2 ATP molecules and 2 NADH.

Some cells (due east.g., mature mammalian ruby claret cells) cannot undergo aerobic respiration, so glycolysis is their simply source of ATP. However, about cells undergo pyruvate oxidation and keep to the other pathways of cellular respiration.

Pyruvate Oxidation

In eukaryotes, pyruvate oxidation takes place in the mitochondria. Pyruvate oxidation can only happen if oxygen is available. In this process, the pyruvate created by glycolysis is oxidized. In this oxidation process, a carboxyl group is removed from pyruvate, creating acetyl groups, which compound with coenzyme A (CoA) to course acetyl CoA. This procedure too releases CO₂.

Citric Acrid Bicycle

The citric acid bicycle (also known equally the Krebs cycle) is the 2d pathway in cellular respiration, and it also takes place in the mitochondria. The rate of the cycle is controlled by ATP concentration. When at that place is more ATP available, the rate slows down; when in that location is less ATP the rate increases. This pathway is a closed loop: the final pace produces the compound needed for the kickoff step.

The citric acid cycle is considered an aerobic pathway because the NADH and FADH₂ it produces act as temporary electron storage compounds, transferring their electrons to the next pathway (electron transport chain), which uses atmospheric oxygen. Each plough of the citric acid wheel provides a net gain of CO₂, 1 GTP or ATP, and 3 NADH and 1 FADH₂.

Electron Transport Concatenation

Most ATP from glucose is generated in the electron transport concatenation. It is the only part of cellular respiration that directly consumes oxygen; however, in some prokaryotes, this is an anaerobic pathway. In eukaryotes, this pathway takes place in the inner mitochondrial membrane. In prokaryotes it occurs in the plasma membrane.

The electron send chain is fabricated up of 4 proteins along the membrane and a proton pump. A cofactor shuttles electrons betwixt proteins I–III. If NAD is depleted, skip I: FADH₂ starts on 2. In chemiosmosis, a proton pump takes hydrogens from inside mitochondria to the exterior; this spins the "motor" and the phosphate groups attach to that. The movement changes from ADP to ATP, creating 90% of ATP obtained from aerobic glucose catabolism.

Let's Practice

Now that you lot've reviewed cellular respiration, this practice activeness will help you lot run across how well you know cellular respiration:

Click here for a text-simply version of the activity.

Check Your Understanding

Answer the question(s) below to come across how well you sympathise the topics covered in the previous section. This short quiz doesnot count toward your course in the form, and you tin can retake it an unlimited number of times.

Employ this quiz to bank check your understanding and make up one's mind whether to (i) written report the previous department further or (ii) move on to the next section.

johnsonhartatied.blogspot.com

Source: https://courses.lumenlearning.com/suny-wmopen-biology1/chapter/cellular-respiration/

Share this post