Electron Transport Chain - Podcast Version 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x The electron transport chain (ETC) is the main source of ATP production in the body and is vital for life. The previous stages of respiration generate electron carrier molecules, such as NADH, to be used in the ETC. Clinically, some molecules interfere with the electron transport chain, which can be life-threatening and will be discussed in this article. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More The Electron Transport Chain Complexes The electron transport chain is located in the mitochondria. There are five main protein complexes in the ETC, located in the inner membrane of the mitochondria. These are labelled complexes I, II, III, IV, and V. The two electron carriers, NADH and FADH2, begin the chain by donating their electrons to complex I and complex II respectively. These electrons are then passed along to the next complex in the chain. Energy Generation This process generates energy which is used to pump hydrogen ions into the intermembrane space. In doing so, a proton motive force is generated. This is an electrical and chemical gradient of hydrogen ions between the intermembrane space and the matrix. The main route for protons to re-enter the matrix is via ATP synthase, or complex V. This is key for both pathological and physiological processes and is discussed in uncoupling. ATP synthase allows the proton motive force to be discharged and utilised by the cell. This energy generated by hydrogen ions diffusing back into the matrix via complex V is harnessed, thereby creating ATP from ADP. When the concentration of ATP rises, there is less ADP for ATP synthase to use. Therefore, there is a natural limitation in periods of high respiration to avoid large amounts of ATP from being produced. Conversely, when the concentration of ADP is high, there is a lot of ADP for ATP synthase to use and so more ATP is made. The electrons, meanwhile, combine with the hydrogen ions and oxygen to form water by complex IV. However, this process is not perfect. Electrons can leak out of the electron transport chain and can reduce oxygen, which can produce free radicals such as superoxide and hydrogen peroxide. By OpenStax College (https://commons.wikimedia.org/wiki/File:2508_The_Electron_Transport_Chain.jpg) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons Fig 1Diagram to summarise the electron transport chain. Uncoupling Uncoupling proteins provide an alternative route for proteins to pass into the matrix through the membrane. This is due to the reduced gradient between the matrix and the intermembrane space. Therefore, there is less ATP formed, and, instead, more heat is generated. Physiologically, thermogenin is an uncoupling protein found in brown adipose tissue which allows protons to flow from the intermembrane space into the matrix to generate heat in response to cold. This is especially important in young infants. Clinical Relevance Pathological Uncoupling Uncoupling can also occur pathologically. In contrast to uncoupling proteins, some chemicals increase the permeability of the inner mitochondrial membrane to protons without a need for a protein. This is seen in 2,4-dinitrophenol (DNP) poisoning, where the membrane becomes more permeable to protons. This is also seen in salicylate, which is a by-product of aspirin poisoning. Administration of these drugs results in overheating as the protons diffuse through the membrane and not through ATP synthase.  This means less ATP is produced, in favour of heat. Clinical Relevance Electron Chain Inhibitors By inhibiting a protein in the ETC sequence, the proteins can’t use the energy of the electrons to pump hydrogen ions, and so the chain can’t function. Examples include cyanide and carbon monoxide which inhibit the final electron acceptor. This means that all complexes before that remain coupled with an electron, and so there is no passing of electrons down the chain and no proton motive force established. Therefore, there is minimal ATP production. Do you think you’re ready? Take the quiz below Pro Feature - Quiz Electron Transport Chain Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 More Questions Available Upgrade to TeachMePhysiology Pro Challenge yourself with over 2100 multiple-choice questions to reinforce learning Learn More Frequent questions What is the electron transport chain and its significance in ATP production? The electron transport chain (ETC) is a crucial metabolic pathway located in the mitochondria that generates ATP, the primary energy currency of the cell. It utilises electron carriers like NADH and FADH2 to facilitate the transfer of electrons, ultimately producing ATP through the proton motive force. How do the complexes in the electron transport chain function? The electron transport chain comprises five main protein complexes (I, II, III, IV, and V) embedded in the inner mitochondrial membrane. These complexes work sequentially to accept and transfer electrons, which helps generate a proton gradient essential for ATP synthesis via ATP synthase. What is the role of ATP synthase in the electron transport chain? ATP synthase, also known as complex V, is responsible for synthesising ATP from ADP by harnessing the energy released as protons flow back into the mitochondrial matrix. This process is driven by the proton motive force created during the electron transport chain's operation. What are the clinical implications of uncoupling in the electron transport chain? Uncoupling can occur physiologically through proteins like thermogenin, which generates heat instead of ATP, particularly in brown adipose tissue. Pathologically, compounds like 2,4-dinitrophenol can disrupt ATP production by increasing membrane permeability to protons, leading to overheating and reduced ATP synthesis. How do inhibitors affect the electron transport chain? Inhibitors such as cyanide and carbon monoxide block the electron transport chain by preventing the final electron acceptor from functioning. This inhibition halts the transfer of electrons, disrupts the proton motive force, and significantly decreases ATP production. Rate This Article