These are Glycolysis, the transition reaction, the Krebs cycle also known as the citric acid cycle , and the electron transport chain with chemiosmosis. Glycolysis is a series of reactions that extract energy from glucose by splitting it into 2 molecules of pyruvate.
Glycolysis is a biochemical pathway that evolved long ago and is found in the majority of organisms. In organisms that perform cellular respiration, glycolysis is the first stage of the process.
Before glycolysis begins, glucose must be transported into the cell and phosphorylated. In most organisms, this occurs in the cytosol. Glycolysis does refer to other pathways, one such pathway described is the Entner—Doudoroff pathway. This article concentrates on the EMP pathway. Glycolysis takes place in 10 steps. See figure 7. The enzyme hexokinase phosphorylates glucose using ATP to transfer a phosphate to the glucose molecule to form glucosephosphate. This reaction traps the glucose within the cell.
Glucosephosphate is isomerized into fructosephosphate. This involves the change of an aldose into a ketose. The enzyme phosphoglucose isomerase catalyzes this reaction. A molecule of ATP provides the phosphate group. Phosphofructokinase PFK with magnesium as a cofactor phosphorylates glucosekinase to fructose 1,6-bisphosphate. This enzyme catalyzes the transfer of a phosphoryl group from ATP to fructosephosphate.
This reaction yields ADP and fructose 1, 6-bisphosphate. PFK is a significant enzyme in the regulation of glycolysis. Citric acid is also known to inhibit the action of PFK. These first 3 stages of glycolysis have used up a total of 2 ATP molecules; hence it is known as the investment phase.
The enzyme aldolase is utilized to split fructose 1, 6-bisphosphate into glyceraldehydephosphate GAP and dihydroxyacetone phosphate DHAP. GAP is the only molecule that continues in the glycolytic pathway.
At this point there are two molecules of GAP, the next steps are to fully convert to pyruvate. The phosphate group then attacks the GAP molecule and releases it from the enzyme to yield 1,3 bisphosphoglycerate, NADH, and a hydrogen atom. Phosphoglycerate kinase PGK with the help of magnesium converts 1,3 bisphosphoglycerate to 3-phosphoglycerate by removing a phosphate group. Phosphoglycerate mutase rearranges the position of the phosphate group on 3-phosphoglycerate allowing it to become 2-phosphoglycerate.
Enolase dehydrates 2 phosphoglycerate molecules by removing water. In aerobic respiration, the transition reaction occurs in the mitochondria. Pyruvate moves out of the cytoplasm and into the mitochondrial matrix. In anaerobic conditions, pyruvate will stay in the cytoplasm and be used in lactic acid fermentation instead. The Krebs cycle, or also known as the citric acid cycle was discovered by Hans Adolf Krebs in It can be described as a metabolic pathway that generates energy.
This process happens in the mitochondrial matrix, where pyruvate has been imported following glycolysis. These products are generated per single molecule of pyruvate. The products of the Krebs cycle power the electron transport chain and oxidative phosphorylation.
Acetyl CoA enters the Krebs cycle after the transition reaction has taken place conversion of pyruvate to acetyl CoA. See figure 9. There are 8 steps in the Krebs cycle. 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? They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource. If a media asset is downloadable, a download button appears in the corner of the media viewer.
If no button appears, you cannot download or save the media. Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. A cell is one of the building blocks of life. Cells are membrane-bound groups of organelles that work together to allow it to function. Some of the major organelles include the nucleus, mitochondria, lysosomes, the endoplasmic reticulum, and the Golgi apparatus.
Plant cells also include chloroplasts, which are responsible for photosynthesis. Use these classroom resources to examine how cells function with your students. It's a new name for a new geologic epoch-one defined by our own massive impact on the planet. Similarly, some medications such as certain antibiotics, chemotherapeutics, statins, and anesthetics can also interfere with mitochondrial function and may not be suitable to treat patients that have mitochondrial disorders 3.
To learn more about our GDPR policies click here. If you want more info regarding data storage, please contact gdpr jove. Your access has now expired. Provide feedback to your librarian. If you have any questions, please do not hesitate to reach out to our customer success team. Login processing Autotrophs and Heterotrophs Living organisms require a continuous input of energy to maintain cellular and organismal functions such as growth, repair, movement, defense, and reproduction.
Aerobic Respiration Aerobic respiration occurs in three stages. Anaerobic Respiration Aerobic respiration requires oxygen, however, there are many organisms that live in places where oxygen is not readily available or where other chemicals overwhelm the environment. Photosynthesis Cellular respiration together with photosynthesis is a feature of the transfer of energy and matter, and highlights the interaction of organisms with their environment and other organisms in the community.
Measuring Respiration Scientists can measure the rate of cellular respiration using a respirometer by assessing the rate of exchange of oxygen. Mitochondrial dysfunction and oxidative stress in neurodegenerative diseases. Cyanide poisoning: pathophysiology and treatment recommendations.
Occupational Medicine. Finsterer, J and Segall, L. Drugs interfering with mitochondrial disorders. Drug Chem Toxicol. Please enter your institutional email to check if you have access to this content. Please create an account to get access. Forgot Password? Please enter your email address so we may send you a link to reset your password. To request a trial, please fill out the form below. A JoVE representative will be in touch with you shortly. You have already requested a trial and a JoVE representative will be in touch with you shortly.
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