BIOL 225 Lecture 18.pdf

BIOL 225 Lecture 18.pdf - Lecture 18 Cellular respiration...

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Unformatted text preview: 3/1/17 Lecture 18 Cellular respiration occurs in three stages Today’s lecture Cellular Respiration Lecture 17 Citr ic Acid Cycle BIOL 225 Prof. Liz Allison March 1, 2017 Compartmentalization of functionally related enzymes Where are most citric acid cycle enzymes located? There are some reactions taking place in the matrix, the fluid space, not the membrane of the mitochondria. A preliminary step: Oxidation of pyruvate Catalyzed by the pyruvate dehydrogenase complex The oxidation of pyruvate is a preliminary step for the citric acid cycle. The final product has a sulfur in it, with one carbon released on carbon dioxide. This is catalyzed by a large enzyme complex. 1 3/1/17 Key points (you don’t need to memorize the cycle) • Carbons donated by acetyl group are ________(oxidized or reduced?) to CO2 • Electrons/protons are accepted by electron carriers • A specific enzyme is involved at each step Energy storage flavin adenine dinucleotide Energy yield ATP is produced from the citric acid cycle, but just a little bit. In some cell types it is GTP that is released, rather than ATP that is released. The process should be similar overall. There is also energy storage in the form of electron carriers, like NADH and FADH. Glucose becomes pyruvate. This enters the mitochondria through pores. This then is transfered to acetyl coA and then into the citric acid cycle. Carbons donated to CO2 are oxidized (the electrons go to carriers which are reduced). Electron Transport Chain Are NADH and FADH2 oxidized or reduced? • Complexes I, III, and IV use the potential energy released by the redox reactions Lipid soluble These now enter into the electron transport chain. These are simply a serious of redox reactions going from high to low free energy. Oxygen is the final electron accpetor (which is why fermentation occurs when there isn't any to accept at the end • Pump protons into the intermembrane space The pink is the cristae, or mitochondrial matrix, and the blue is the intermembrane space. 2 3/1/17 Up close and personal with one of the electron carriers: A Murder Mystery from Bitter Almonds by D. L. Sayers Cyt cox (Fe ) + e → Cyt cred (Fe ) 3+ − 2+ “Noyeau?” heme Cytochrome c = protein + heme group Cytochrome C contains a protein and a heme group with iron held in a nitrogen ring. The iron is what actually "carries" the electron, being oxidized or reduced. “I see that means something to you, doctor.” “It does, indeed. Noyeau is a liqueur flavored with the oil of bitter almonds, or peachstones—correct me if I’m wrong, Mr. Egg—and contains, therefore, a small proportion of hydrocyanic acid.” 3 3/1/17 “That’s it. Of course, in the ordinary way, there isn’t enough of it to hurt anybody in a single glassful, or even two. But if you let a bottle stand long enough, the oil will rise to the top, and the first glass out of an old bottle of Noyeau has been known to cause death.” Hydrocyanic acid (hydrogen cyanide) HCN Which component of the electron transport chain is inhibited? Cyanide can actually interact with the iron, accepting the electrons from the acid rather than from the chain. Thus, the electron transport chain is disrupted, because it The discovery of ATP synthase: The rotary engine in the cell Key Points • Energy is released as electrons pass down the chain • Energy is harnessed: Oxidative phosphorylation* ADP → ATP *Compare with substrate-level phosphorylation in glycolysis Chemiosmosis The energy released in each step is harnessed for oxidative phosphorylation. This is different from substrate level phosphorylation. This enzyme is a big protein complex that has mechanical properties. It acts like a rotary engine, spinning like a turbine with a proton flow. As protons flow down the gradient they run through this one subunit called the Fo unit, which turns the unit to turn the rotor, which changes the conformation allowing the addition of phosphate to the ATP. This is called chemiosmosis. 4 3/1/17 How are the electron transport chain and ATP production linked? 1. Produce vesicles from artificial membranes. Vesicle Bacteriorhodopsin ATP synthase 2. Add bacteriorhodopsin. Light Light 3. Illuminate vesicle. Does ATP really require the electron transport chain? They made a fake system to test. ATP is produced within the vesicle, in the absence of the electron transport chain. CONCLUSION: The linkage between electron transport and ATP synthesis is indirect; the movement of protons drives the synthesis of ATP. QUESTION: If bacteriorhodopsin were not available, how else could the researchers have generated a proton gradient? You just need an electron gradient in order to produce ATP. If there is a gradient generated another way, you could just add a fuck ton of acid to create that gradient. Recommended readings from the textbook Chapter 9: p. 196-206, 208-209 Cellular Respiration Movie This graphic sums up the cellular respiration cycle overall. You should probably be able to recreate this. 5 ...
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