Oxidative Phosphorylation PDF

Republic of the Philippines WESTERN MINDANAO STATE UNIVERSITY COLLEGE OF MEDICINE Zamboanga City BIOCHEMISTRY MODULE Prepared by: FARR KRIZHA TANGKUSAN, RN, MD RESPIRATION...

Republic of the Philippines WESTERN MINDANAO STATE UNIVERSITY COLLEGE OF MEDICINE Zamboanga City BIOCHEMISTRY MODULE Prepared by: FARR KRIZHA TANGKUSAN, RN, MD RESPIRATION ▪ 2 electron carriers used in the ETC: ▪ Respiration – a process by which cells derive energy with ▪ Nicotinamide Adenine Dinucleotide (NAD+) a controlled reaction between H+ and O2; the end ▪ Flavin Adenine Dinucleotide (FAD) product being water. ▪ NAD+ and FAD receive electrons (i.e., they undergo ▪ Aerobic organisms are able to capture a far greater REDUCTION) from other substances to form NADH and proportion of the available free energy of respiratory FADH2 substrates than anaerobic organisms. ▪ NADH and FADH2 each donate electrons to a specialized ▪ The objective of respiration is to produce ATP. set of electron carriers in the inner mitochondrial ▪ Energy is released from oxidation reactions in the form of membrane electrons. ▪ Electrons are shuttled by electron carriers (e.g. NAD+) to an electron transport chain ▪ Electron energy is converted to ATP in the electron transport chain. Remember our mnemonic for oxidation and reduction? METABOLISM So, GEROA. Gain of Electron Reduction Oxidative Agent ▪ Metabolism is the sum of the chemical reactions in an organism. If you think of ATP as cash, NADH and FADH2 are ▪ Catabolism is the energy-releasing processes. analogous to cheques. They have to be converted to ▪ Anabolism is the energy-using processes. ▪ Catabolism provides the building blocks and energy for cash in a bank (ETC and ATP synthase) before they can anabolism. be made useful. ▪ Electrons are come from electron carriers and they travel through the electron transport chain where the electrons final destination is oxygen which will help to reduce Oxygen to form water. So oxygen is known as final acceptor. ▪ Electrons captured from donor molecules are transferred through 4 complexes. OXIDATIVE PHOSPHORYLATION ▪ Oxidative phosphorylation is the process by which the energy stored in NADH and FADH2 is used to produce ATP. COMPLEX I ▪ NADH-coenzyme Q oxidoreductase, also known as NADH dehydrogenase or complex I, is the first protein in the electron transport chain. * Mitochondrial disorders severely affect muscle and nervous tissue because they have a high demand for ATP. ELECTRON TRANSPORT CHAIN (ETC) ▪ Final common pathway by which electrons from the different fuels of the body flow to oxygen. ▪ Located in the mitochondria, specifically, in the inner membrane.  ▪ In Complex I, in which NADH is oxidized to NAD+ & H+, this process obtain two electrons which will first given to FMN (flavin mononucleotide) from here the electrons are transferred one at a time through a series of iron sulfur center than 2 electrons create a proton gradient which bring 2 hydrogen ions from the matrix and bound to ubiquinone and as a biased ubiquinone, it will reduced to ubiquinol (QH2). ▪ Complex I can transfer 4 protons from the matrix inner membrane space. It will be seen that transfer of four protons into inner membrane space is equivalent to formation of one ATP molecule. ▪ Cytochromes are protein containing heme group. ▪ When Electrons are donated from NADH to NADH COMPLEX II dehydrogenase, a large protein complex that pumps ▪ Succinate-Q oxidoreductase, also known as complex 2 or protons across the inner membrane. succinate dehydrogenase, (from the citric acid cycle) is a ▪ Then, electrons are transported to the coenzyme Q (Q), second entry point to the electron transport chain. also termed ubiquinone; then ubiquinone travel to the inner membrane and associate with the subunit of complex III. ▪ In complex III cytochrome c is not a part of any enzyme complex, is freely soluble and occurs in the inter membrane space ▪ Cytochrome c is also called mobile protein because it travels to the inter membrane space and attached or bind to the complex IV cytochrome oxidase. ▪ It contains FAD (Flavin adenine dinucleotide) and Fe-S COMPLEX IV centers; it lacks proton pump activity. It oxidizes ▪ Cytochrome c oxidase succinate to fumarate and reduces ubiquinone. The two ▪ The final step of ETC is the reduction of molecular oxygen hydrogen atoms are first taken up by FAD to form FADH2 by electrons derived from cyt-c. then passed through a series of iron sulfur centers and ▪ Complex IV consist of 3 important subunits: passed to ubiquinone. 1) Subunit 1 has two heme group a and a3 ▪ As this reaction releases less energy than the oxidation of 2) Subunit 2 contains two Cu ions NADH, complex II does not transport protons across the 3) Subunit 3 is essential for the activity of complex IV membrane and does not contribute to the proton gradient. ▪ For this reason, whereas transfer of two hydrogen from NADH to coenzyme Q by the complex I results in formation of one ATP, the transfer of two H atoms from FADH2 to coenzyme Q does not produce protons that will cross the membrane. COENZYME Q ▪ Coenzymes Q (ubiquinone) flows to the inner membrane ▪ Its purpose is to carry electron through different complexes because it is a mobile protein where the ▪ The cytochrome oxidase complexes then transfer complexes are stationary coenzymes travel to the inner electrons from cytochrome c to oxygen, the terminal membrane with 2 electrons. It would not associate with electron acceptor, and water is formed as the product. complex 2 but it would associate with complex 3. ▪ Cytochrome oxidase also pumps 2 protons across the membrane. ▪ The transfer of protons generates a proton motive force across the membrane of the mitochondrion. COMPLEX III ▪ Cytochrome b-c complex also called cytochrome c oxireductase ▪ Complex 3 has a few important subunit or 3 important structure: 1) Iron sulfur (Fe-S) protein 2) Cytochrome b 3) Cytochrome c ▪ Electrons are transported between all these complexes and where will rise at oxygen so oxygen is final electron acceptor.  ▪ These electrons are come from 1NADH and so now if we ATP SYNTHASE calculate all the protons pumped from 1 NADH to all the ▪ The ATP synthase has two distinct subunits: complexes: 1) The transmembrane F0 subunit, which contains a protein channel for the flow of protons. Complex I = 4 protons 2) The F1 subunit, which protrudes into the matrix Complex III = 4 protons space and catalyzes the synthesis of ATP from ADP Complex IV = 2 protons and inorganic phosphate. These 10 hydrogen ion it would go through the ATP synthase to produce ATP CHEMIOSMOTIC THEORY ▪ According to this theory, the transfer of electrons down an electron transport system through a series of oxidation- reduction reactions releases energy. ▪ This creates an electrochemical gradient across the inner membrane. The energized state of the membrane as a result of this charge separation is called proton motive force or PMF. ▪ The chemiosmotic theory was developed by the British biochemist, Peter Mitchell which explain the mechanism of ATP formation. ▪ ▪ As electrons are transferred along the electron Transport chain from electron donor to electron acceptor in the inner mitochondrial membrane, free energy is released. This energy allows certain carriers in the chain to transport hydrogen ions (protons) which thus contains a higher concentration of protons than the matrix. ▪ As the stalk rotates in one direction, it induces conformational changes in the proteins of the F1 ▪ subunit, which, in turn, catalyze the synthesis of ATP - thereby converting the mechanical energy of stalk rotation to chemical bond energy. ▪ Approximately 4 protons must pass through the ATP synthase complex for 1 ATP molecule to be synthesized. ▪ The hydrogen concentration is much greater in the inter membrane space than in the matrix, thus generating an electrochemical proton gradient. These gradient drives proton back across the inner membrane through the ATP synthase (shown in gray) that catalyzes the synthesis of ▪ This proton motive force provides the energy necessary ATP from ADP and inorganic phosphate (Pi). for enzymes called ATP synthases, to catalyze the synthesis of ATP from ADP and phosphate. ▪ This generation of ATP occurs as the protons across the membrane through the ATP synthase complexes re-enter the matrix of the mitochondria. As the protons move down the concentration gradient through the ATP synthase, the energy released causes the rotor (F0) and stalk of the ATP synthase to rotate. The mechanical energy from this rotation is converted into chemical energy as phosphate is added to ADP to form ATP in the catalytic head (F1 domain) ATP is generated by the phosphorylation of ADP.  SHUTTLE SYSTEMS ▪ Transfer of reduced coenzymes from cytoplasm into the mitochondria to ETC 1) Malate-aspartate shuttle 2) Glycerol-3-Phosphate shuttle MALATE-ASPARTATE SHUTTLE ▪ Found in: liver, kidney, and heart ▪ Results in NADH in the matrix ▪ Complicated, but free! POISONS THAT INHIBIT THE RESPIRATORY CHAIN 1. Barbiturates such as amobarbital inhibit electron transport via Complex I by blocking the transfer from Fe-S to Q. At sufficient dosage, they are fatal in vivo. 2. Antimycin A and dimercaprol inhibit the respiratory chain at Complex III. 3. H2S, carbon monoxide, and cyanide inhibit Complex IV and can therefore totally arrest respiration. 4. Malonate is a competitive inhibitor of Complex II. 5. Atractyloside inhibits oxidative phosphorylation by inhibiting the transporter of ADP into and ATP out of the mitochondrion. 6. Oligomycin completely blocks oxidation and phosphorylation by blocking the flow of protons through ATP synthase. Uncouplers ▪ dissociate oxidation in the respiratory chain from phosphorylation. ▪ These compounds are toxic in vivo, causing respiration to become uncontrolled, since the rate is no longer limited by the concentration of ADP or Pi. ▪ Examples: 1) 2,4-dinitrophenol 2) Thermogenin (or the uncoupling protein) GLYCEROL 3-P SHUTTLE ▪ Found in: skeletal muscle and brain ▪ Electrons enter at Q ▪ Easier, but costly!