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TAMU BIOL 213 - Electron Transport Chain of Cellular Respiration and Photosynthesis
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BIOL 213 1st Edition Lecture 11 Outline of Last Lecture I. Cellular respirationa. Introductory informationII. Glycolysisa. Main pointsb. Energy investment stagec. Cleavage from 6C to 3C staged. Energy production stageIII. What happens to pyruvatea. Anaerobic vs aerobic conditionsIV. What happens wherea. Glycolysis in the cytosolb. Everything else in the mitochondriaV. Citric Acid Cycle / TCA Cycle / Krebs Cyclea. Main pointsb. The processVI. Electron transport chain and oxidative phosphorylationVII. Basic reviewOutline of Current Lecture These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.I. Electron transport chain of cellular respirationa. Review of main pointsb. The stepsc. What if O2 were removedd. Redox potentiale. Electron transfer between moleculesf. Proton gradientII. Net ATP yield for cellular respirationa. ~30 ATP per 1 glucoseIII. Photosynthesisa. Chloroplastb. Two stagesc. Chlorophylld. Electron transportCurrent LectureI. Electron transport chain of cellular respirationa. Review of main pointsi. Electrons are transported down a chain of membrane-bound proteins of the inner mitochondrial membraneii. The energy from this transportation is used to create a H+ gradient in the intermembrane spaceiii. The energy from this gradient is used to drive ATP synthase which makes ATP via oxidative phosphorylationb. The steps of the transport i. NADH carries two electrons to the beginning of the chain from the Krebs cycleii. The electrons are passed to the first protein – NADH dehydrogenase complex1. Protons are pumped into the intermembrane spaceiii. The electrons are passed to a carrier molecule called ubiquinone1. Ubiquinone is reduced2. It can diffuse along the membrane to accept and donate electrons3. This is not a protein4. It is a molecule that is also in the inner membrane that shuttles electrons between the 1st and 2nd protein5. Ubiquinone with only one electron is very unstable6. Electrons from FADH2 are passed directly to ubiquinonea. This is because these electrons are lower in energy than those of NADHiv. Ubiquinone passes the electrons to the 2nd protein of the chain (cytochrome b-c1; but we don’t have to know the name)1. Protons are pumped into the intermembrane spacev. The electrons are passed to another carrier molecule called cytochrome c1. This is a peripheral protein on the intermembrane space-side of the inner membrane2. It can diffuse along the membrane to accept and donate electronsvi. Cytochrome c passes the electrons to the 3rd protein – cytochrome oxidase complex1. Protons are pumped into the intermembrane space2. This is the protein that reduces O2 into H2O!3. It takes in 4 H+, 4 e-, and 1 O2 and puts out 2H2O4. THIS IS THE ONLY STEP IN CELLULAR RESPIRATION WHERE O2 IS DIRECTLY UTILIZEDc. What would happen if O2 were removed?i. The electrons wouldn’t have anywhere to goii. They would pile up in the electron chainiii. NADH wouldn’t be able to unload its electronsiv. NADH would pile upv. There wouldn’t be enough NAD+ vi. This would cause the Citric Acid Cycle to stop working vii. The cell would switch to fermentation so that the NAD+ required for glycolysis will be replenishedd. Redox potentiali. This is the energy stored in the affinity of the molecule for the electronii. If redox potential is negative, it means the molecule has a low affinity for the electron and wants to get rid of itiii. A positive redox potential means the molecule has a high affinity for the electron and wants to keep itiv. Electrons want to go from negative redox potentials to positive redox potentialsv. This is how the electrons of the transport chain move down the proteins: they move from the most negative to the most positive redox potential1. The higher up a molecule is in the chain, the more negative its redox potential is2. NADH has the most negative3. Therefore the electrons move from NADH to the more positive NADH dehydrogenase complex4. But the NADH dehydrogenase complex is more negative than the ubiquinone, so the electrons will move to the ubiquinone5. And so on, down the chain6. When H2O is formed, there is no energy in its redox potential because it’s so positive that the electrons don’t want to leavevi. It is possible for the electrons of the transport chain to move directly from the most negative redox potential of NADH to the most positive of O2 1. But the cell doesn’t do this for similar reasons as to why it doesn’t burn glucose for energy – too much energy would be lost as heat, it couldn’t be utilized efficiently, and it might kill the celle. How electrons are transferred between molecules of the chaini. Each protein has metal atoms that the electrons bind toii. Iron-sulfur centers; heme (iron atoms); and copper atomsiii. NADH dehydrogenase – has iron-sulfur centers (these have the most negative redox potential)1. These are usually bound to the sulfur of cysteineiv. Ubiquinone – doesn’t have any because it’s not a protein!v. Protein 2 – has heme (iron atoms)vi. Cytochrome c – has heme (iron atoms)vii. Cytochrome oxidase – has heme (iron atoms) and copper atomsf. Proton gradienti. This, as we know, is created using the energy from the redox potentials of the transport chain to pump H+ into the inner membrane spaceii. Because there are more H+ ions in the intermembrane space, it has a lower pH than the matrix1. I.e. the intermembrane space is more acidic than the matrixiii. It also creates a negative membrane potential1. Because there is more positive charge outside of the matrixiv. The energy of both the proton concentration gradient and electrochemical gradient are utilized by ATP synthase to make ATP1. The electrochemical gradient is more influential on the H+ ions than the concentration so it provides more energy2. H+ ions flow into the matrix through ATP synthase, causing it to spin, which causes physical distortions of ADP and Pi, which cause them to join together to create ATPv. It is also used to drive coupled transport that bring other necessary molecules into the matrix1. The electrochemical gradient is used to transport ADP3- and ATP4- into and out of the mitochondriaa. ATP is pumped out and ADP is pumped inb. The charge on ATP is more negative than on ADPc. Therefore the change in membrane potential when 1 ADP is pumped in and 1 ATP is pumped out is +1d. This is energetically favorablee. The transport protein is


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TAMU BIOL 213 - Electron Transport Chain of Cellular Respiration and Photosynthesis

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