What is produced during cellular respiration

Below reviews some of the principal parts of these steps and the products of Krebs cycle:. Acetyl CoA joins with oxaloacetate releasing the CoA group and producing citrate, a six-carbon molecule. The enzyme involved in this process is citrate synthase. Citrate is converted to isocitrate by the enzyme aconitase.

This involves the removal then the addition of water. The ketone is then decarboxylated i. CO 2 removed by isocitrate dehydrogenase leaving behind alpha-ketoglutarate which is a 5-carbon molecule. Isocitrate dehydrogenase, is central in regulating the speed of the Krebs cycle citric acid cycle.

Oxidative decarboxylation takes place by alpha-ketoglutarate dehydrogenase. Succinyl-CoA is converted to succinyl phosphate, and then succinate.

Succinate thiokinase other names include succinate synthase and Succinyl coenzyme A synthetase , converts succinyl-CoA to succinate, and free coenzyme A. Firstly, the coenzyme A at the succinyl group is substituted by a hydrogen phosphate ion. Succinyl phosphate then transfers its phosphoric acid residue to guanosine diphosphate GDP so that GTP and succinate are produced. Succinate is oxidized to fumarate by succinate dehydrogenase.

Flavin adenine dinucleotide FAD is the coenzyme bound to succinate dehydrogenase. FADH 2 is formed by the removal of 2 hydrogen atoms from succinate. This releases energy that is sufficient to reduce FAD. FADH remains bound to succinate dehydrogenase and transfers electrons directly to the electron transport chain.

Succinate dehydrogenase performs this process inside the mitochondrial inner membrane which allows this direct transfer of the electrons.

L-malate is formed by the hydration of fumarate. The enzyme involved in this reaction is fumarase. In the final step, L-malate is oxidized to form oxaloacetate by malate dehydrogenase. Where is oxygen used in cellular respiration? It is in the stage involving the electron transport chain. The electron transport chain is the final stage in cellular respiration. It occurs on the inner mitochondrial membrane and consists of several electron carriers.

The purpose of the electron transport chain is to form a gradient of protons that produces ATP. It moves electrons from NADH to FADH 2 to molecular oxygen by pumping protons from the mitochondrial matrix to the intermembrane space resulting in the reduction of oxygen to water.

Therefore, the role of oxygen in cellular respiration is the final electron acceptor. It is worth noting that the electron transport chain of prokaryotes may not require oxygen. Other chemicals including sulfate can be used as electron acceptors in the replacement of oxygen. Four protein complexes are involved in the electron transport chain. These electrons are then shuttled down the remaining complexes and proteins.

They are passed into the inner mitochondrial membrane which slowly releases energy. The electron transport chain uses the decrease in free energy to pump hydrogen ions from the matrix to the intermembrane space in the mitochondrial membranes. This creates an electrochemical gradient for hydrogen ions. Overall, the end products of the electron transport chain are ATP and water. See figure The process described above in the electron transport chain in which a hydrogen ion gradient is formed by the electron transport chain is known as chemiosmosis.

After the gradient is established, protons diffuse down the gradient through ATP synthase. Chemiosmosis was discovered by the British Biochemist, Peter Mitchell. In fact, he was awarded the Nobel prize for Chemistry in for his work in this area and ATP synthesis.

How much ATP is produced in aerobic respiration? What are the products of the electron transport chain? Glycolysis provides 4 molecules of ATP per molecule of glucose; however, 2 are used in the investment phase resulting in a net of 2 ATP molecules. Finally, 34 molecules of ATP are produced in the electron transport chain figure Only 2 molecules of ATP are produced in fermentation.

This occurs in the glycolysis phase of respiration. Therefore, it is much less efficient than aerobic respiration; it is, however, a much quicker process. And so essentially, this is how in cellular respiration, energy is converted from glucose to ATP. And by glucose oxidation via the aerobic pathway, more ATPs are relatively produced.

What are the products of cellular respiration? The biochemical processes of cellular respiration can be reviewed to summarise the final products at each stage. Mitochondrial dysfunction can lead to problems during oxidative phosphorylation reactions. These mutations can lead to protein deficiencies. For example, complex I mitochondrial disease is characterized by a shortage of complex I within the inner mitochondrial membrane. This leads to problems with brain function and movement for the individual affected.

People with this condition are also prone to having high levels of lactic acid build-up in the blood which can be life-threatening. Complex I mitochondrial disease is the most common mitochondrial disease in children. To date, more than different mitochondrial dysfunction syndromes have been described as related to problems with the oxidative phosphorylation process.

Furthermore, there have been over different point mutations in mitochondrial DNA as well as DNA rearrangements that are thought to be involved in various human diseases. There are many different studies ongoing by various research groups around the world looking into the different mutations of mitochondrial genes to give us a better understanding of conditions related to dysfunctional mitochondria.

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 accumulate within the matrix space. Therefore, a concentration gradient forms in which hydrogen ions diffuse out of the matrix space by passing through ATP synthase.

Figure 7. The electron transport chain is a series of electron transporters embedded in the inner mitochondrial membrane that shuttles electrons from NADH and FADH 2 to molecular oxygen.

In the process, protons are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water. The electron transport 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, it enters the body through the respiratory system.

Electron transport is a series of redox reactions that resemble a relay race or bucket brigade in that electrons are passed rapidly from one component to the next, to the endpoint of the chain where the electrons reduce molecular oxygen, producing water. There are four complexes composed of proteins, labeled I through IV in Figure 7, and the aggregation of these four complexes, together with associated mobile, accessory electron carriers, is called the electron transport chain.

The electron transport chain is present in multiple copies in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes. Note, however, that the electron transport chain of prokaryotes may not require oxygen as some live in anaerobic conditions.

The common feature of all electron transport chains is the presence of a proton pump to create a proton gradient across a membrane. To start, two electrons are carried to the first complex aboard NADH.

FMN, which is derived from vitamin B 2 , also called riboflavin, is one of several prosthetic groups or co-factors in the electron transport chain. A prosthetic group is a non-protein molecule required for the activity 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 complex I is NADH dehydrogenase and is a very large protein, containing 45 amino acid chains. Complex I can pump four hydrogen ions across the membrane from the matrix into the intermembrane space, and it is in this way that the hydrogen ion gradient is established and maintained between the two compartments separated by the inner mitochondrial membrane.

The compound connecting the first and second complexes to the third is ubiquinone Q. The Q molecule is lipid soluble and freely moves through the hydrophobic core of the membrane.

Once it is reduced, QH 2 , ubiquinone delivers its electrons to the next complex in the electron transport chain. This enzyme and FADH 2 form a small complex that delivers electrons directly to the electron transport chain, bypassing the first complex.

Since these electrons bypass and thus do not energize the proton pump in the first complex, fewer ATP molecules are made from the FADH 2 electrons. The number of ATP molecules ultimately obtained is directly proportional to the number of protons pumped across the inner mitochondrial membrane. The third complex is composed of cytochrome b, another Fe-S protein, Rieske center 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 it carries electrons, not oxygen. The heme molecules in the cytochromes have slightly different characteristics due to the effects of the different proteins binding 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 fourth 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 only one at a time. The fourth complex is composed of cytochrome proteins c, a, and a 3. This complex contains two heme groups one in each of the two cytochromes, a, and a 3 and three copper ions a pair of Cu A and one Cu B in cytochrome a 3.

The cytochromes hold an oxygen molecule very tightly between the iron and copper ions until the oxygen is completely reduced. The reduced oxygen then picks up two hydrogen ions from the surrounding medium to make water H 2 O. The removal of the hydrogen ions from the system contributes to the ion gradient used in the process of chemiosmosis.

In chemiosmosis, the free energy from the series of redox reactions just described is used to pump hydrogen ions protons across 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 aid 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 Figure 8.

This complex protein acts as a tiny generator, turned by the force of the hydrogen ions diffusing through it, 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. Figure 8. 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 as a weight-loss drug. What effect would you expect DNP to have on the change in pH across the inner mitochondrial membrane? Why do you think this might be an effective weight-loss drug?

Chemiosmosis Figure 9 is used to generate 90 percent of the ATP made during aerobic glucose catabolism; it is also the method used in the light reactions of photosynthesis to harness the energy of sunlight in the process of photophosphorylation. Recall that the production 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 part of a glucose molecule. At the end 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. Figure 9. Cyanide inhibits cytochrome c oxidase, a component of the electron transport chain.

If cyanide poisoning occurs, would you expect the pH of the intermembrane space to increase or decrease? What effect would cyanide have on ATP synthesis?

The number of ATP molecules generated from the catabolism of glucose varies. For example, the number of hydrogen ions that the electron transport chain complexes can pump through the membrane varies between species. Another source of variance stems from the shuttle of electrons across the membranes of the mitochondria. The NADH generated from glycolysis cannot easily enter mitochondria.

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 energy extraction.

Moreover, the five-carbon sugars that form nucleic acids are made from intermediates in glycolysis. Certain nonessential amino acids can be made from intermediates of both glycolysis and the citric acid cycle. In this way, cellular respiration is an example of energy coupling: glucose is broken down in an exothermic reaction, and then the energy from this reaction powers the endothermic reaction of the formation of ATP. Cellular respiration involves many chemical reactions, but they can all be summed up with this chemical equation:.

In words, the equation shows that glucose C 6 H 12 O 6 and oxygen O 2 react to form carbon dioxide CO 2 and water H 2 O , releasing energy in the process. Because oxygen is required for cellular respiration, it is an aerobic process. Cellular respiration occurs in the cells of all living things, both autotrophs and heterotrophs. All of them burn glucose to form ATP. The reactions of cellular respiration can be grouped into three stages: glycolysis, the Krebs cycle also called the citric acid cycle , and electron transport.

Figure 4. The first stage of cellular respiration is glycolysis , which happens in the cytosol of the cytoplasm. Enzymes split a molecule of glucose into two molecules of pyruvate also known as pyruvic acid.

This occurs in several steps, as summarized in the following diagram. Energy is needed at the start of glycolysis to split the glucose molecule into two pyruvate molecules which go on to stage II of cellular respiration. The energy needed to split glucose is provided by two molecules of ATP; this is called the energy investment phase. As glycolysis proceeds, energy is released, and the energy is used to make four molecules of ATP; this is the energy harvesting phase.

As a result, there is a net gain of two ATP molecules during glycolysis. During this stage, high-energy electrons are also transferred to molecules of NAD to produce two molecules of NADH, another energy-carrying molecule. Before pyruvate can enter the next stage of cellular respiration it needs to be modified slightly.

The transition reaction is a very short reaction which converts the two molecules of pyruvate to two molecules of acetyl CoA, carbon dioxide, and two high energy electron pairs convert NAD to NADH. Before you read about the last two stages of cellular respiration, you need to know more about the mitochondrion , where these two stages take place.

A diagram of a mitochondrion is shown in Figure 4. The structure of a mitochondrion is defined by an inner and outer membrane. This structure plays an important role in aerobic respiration. As you can see from the figure, a mitochondrion has an inner and outer membrane. The space between the inner and outer membrane is called the intermembrane space. The space enclosed by the inner membrane is called the matrix.

The second stage of cellular respiration the Krebs cycle takes place in the matrix. The third stage electron transport happens on the inner membrane. Recall that glycolysis produces two molecules of pyruvate pyruvic acid , which are then converted to acetyl CoA during the short transition reaction.

These molecules enter the matrix of a mitochondrion, where they start the Krebs cycle also known as the Citric Acid Cycle. The reason this stage is considered a cycle is because a molecule called oxaloacetate is present at both the beginning and end of this reaction and is used to break down the two molecules of acetyl CoA.

The reactions that occur next are shown in Figure 4. This produces citric acid, which has six carbon atoms. Cellular respiration occurs in the cells of all living things, both autotrophs and heterotrophs. All of them catabolize glucose to form ATP. The reactions of cellular respiration can be grouped into three main stages and an intermediate stage: glycolysis , Transformation of pyruvate , the Krebs cycle also called the citric acid cycle , and Oxidative Phosphorylation. The first stage of cellular respiration is glycolysis.

ATP is produced in this process which takes place in the cytosol of the cytoplasm. Enzymes split a molecule of glucose into two molecules of pyruvate also known as pyruvic acid. Glucose is first split into glyceraldehyde 3-phosphate a molecule containing 3 carbons and a phosphate group.

This process uses 2 ATP. Next, each glyceraldehyde 3-phosphate is converted into pyruvate a 3-carbon molecule. Energy is needed at the start of glycolysis to split the glucose molecule into two pyruvate molecules. These two molecules go on to stage II of cellular respiration.

The energy to split glucose is provided by two molecules of ATP. As glycolysis proceeds, energy is released, and the energy is used to make four molecules of ATP. As a result, there is a net gain of two ATP molecules during glycolysis. In eukaryotic cells, the pyruvate molecules produced at the end of glycolysis are transported into mitochondria, which are sites of cellular respiration. If oxygen is available, aerobic respiration will go forward.

In mitochondria, pyruvate will be transformed into a two-carbon acetyl group by removing a molecule of carbon dioxide that will be picked up by a carrier compound called coenzyme A CoA , which is made from vitamin B 5. Acetyl CoA can be used in a variety of ways by the cell, but its major function is to deliver the acetyl group derived from pyruvate to the next pathway step, the Citric Acid Cycle.

Before you read about the last two stages of cellular respiration, you need to review the structure of the mitochondrion, where these two stages take place. The space between the inner and outer membrane is called the intermembrane space. The space enclosed by the inner membrane is called the matrix. The second stage of cellular respiration, the Krebs cycle, takes place in the matrix.

The third stage, electron transport, takes place on the inner membrane. Recall that glycolysis produces two molecules of pyruvate pyruvic acid. Pyruvate, which has three carbon atoms, is split apart and combined with CoA, which stands for coenzyme A. The product of this reaction is acetyl-CoA. These molecules enter the matrix of a mitochondrion, where they start the Citric Acid Cycle. The third carbon from pyruvate combines with oxygen to form carbon dioxide, which is released as a waste product.

High-energy electrons are also released and captured in NADH. This produces citric acid, which has six carbon atoms. This is why the Krebs cycle is also called the citric acid cycle. After citric acid forms, it goes through a series of reactions that release energy. This energy is captured in molecules of ATP and electron carriers.