The potential energy of this gradient is used to generate ATP. The entirety of this process is called oxidative phosphorylation. The electron transport chain Figure 4. Oxygen continuously diffuses into plants for this purpose. In animals, oxygen enters the body through the respiratory system. Electron transport is a series of chemical reactions that resembles a bucket brigade in that electrons are passed rapidly from one component to the next, to the endpoint of the chain where oxygen is the final electron acceptor and water is produced.
There are four complexes composed of proteins, labeled I through IV in Figure 4. The electron transport chain is present in multiple copies in the inner mitochondrial membrane of eukaryotes and in the plasma membrane of prokaryotes.
In each transfer of an electron through the electron transport chain, the electron loses energy, but with some transfers, the energy is stored as potential energy by using it to pump hydrogen ions across the inner mitochondrial membrane into the intermembrane space, creating an electrochemical gradient. 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 affect would cyanide have on ATP synthesis? As they are passed from one complex to another there are a total of four , the electrons lose energy, and some of that energy is used to pump hydrogen ions from the mitochondrial matrix into the intermembrane space.
In the fourth protein complex, the electrons are accepted by oxygen, the terminal acceptor. The oxygen with its extra electrons then combines with two hydrogen ions, further enhancing the electrochemical gradient, to form water.
If there were no oxygen present in the mitochondrion, the electrons could not be removed from the system, and the entire electron transport chain would back up and stop.
The mitochondria would be unable to generate new ATP in this way, and the cell would ultimately die from lack of energy. This is the reason we must breathe to draw in new oxygen. In the electron transport chain, the free energy from the series of reactions just described is used to pump hydrogen ions across the membrane.
Hydrogen ions diffuse through the inner membrane through an integral membrane protein called ATP synthase Figure 4. This complex protein acts as a tiny generator, turned by the force of the hydrogen ions diffusing through it, down their electrochemical gradient from the intermembrane space, where there are many mutually repelling hydrogen ions to the matrix, where there are few.
This flow of hydrogen ions across the membrane through ATP synthase is called chemiosmosis. Chemiosmosis Figure 4. The result of the 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 electron transport system, the electrons are used to reduce an oxygen molecule to oxygen ions.
Chapter Behavior. Chapter Ecosystems. Chapter Population and Community Ecology. Chapter Biodiversity and Conservation. Chapter Speciation and Diversity. Chapter Natural Selection. Chapter Population Genetics. Chapter Evolutionary History.
Chapter Plant Structure, Growth, and Nutrition. Chapter Plant Reproduction. Chapter Plant Responses to the Environment. Full Table of Contents. This is a sample clip. Sign in or start your free trial. JoVE Core Biology. Previous Video Next Video. Next Video 8. Embed Share. 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. If you need immediate assistance, please email us at subscriptions jove. Thank You. Please enjoy a free hour trial. In order to begin, please login. Please click here to activate your free hour trial. Electrons are passed rapidly from one component to the next to the endpoint of the chain, where the electrons reduce molecular oxygen, producing water.
This requirement for oxygen in the final stages of the chain can be seen in the overall equation for cellular respiration, which requires both glucose and oxygen. A complex is a structure consisting of a central atom, molecule, or protein weakly connected to surrounding atoms, molecules, or proteins.
The electron transport chain is an aggregation of four of these complexes labeled I through IV , together with associated mobile electron carriers. The electron transport chain is present in multiple copies in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes. The electron transport chain : 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.
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 can be organic or inorganic and are non-peptide molecules bound to a protein that facilitate its function.
Prosthetic groups include co-enzymes, which are the prosthetic groups of enzymes. Complex I can pump four hydrogen ions across the membrane from the matrix into the intermembrane space; 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 to 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 heme group. 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, which makes 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 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 produce water H 2 O. The removal of the hydrogen ions from the system also contributes to the ion gradient used in the process of chemiosmosis.
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