Biochemistry 2- Electron Transport Chain and Oxidative Phosphorylation – Flashcards
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How are NADH and FADH transported into mitochondria?
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NADH never passes through the membrane directly, and instead uses reducing equivalents to be shuttled across. FADH passes through the membrane
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Is NADH shuttling required for glycolysis, pyruvate activation, and/or the citric acid cycle?
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Only for glycolysis and activation of pyruvate, not for the citric acid cycle (already next to electron transport chain)
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What are the 2 shuttle systems for NADH? Where are each found?
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1) DHAP/G3P shuttle- Brain 2) Malate/aspartate shuttle- Liver/heart
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How does DHAP/G3P shuttling occur in the brain?
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DHAP is reduced by NADH in the cytosol, and G3P passes through the membrane. It is reoxidized by a flavoprotein in the mitochondrion to G3PDH, which reduce FAD to FADH2 to pass electrons
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How does malate/aspartate shuttling occur in the heart/liver?
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Oxaloacetate is reduced to malate in the cytosol, and passes through the membrane via active transport. Malate is reoxidized by NAD+ back into oxaloacetate. It is then transaminated to aspartate, which crosses back into the cytosol
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What does E0 refer to? Do electrons move from low to high E0, or high to low E0?
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Reduction potential. Electrons move from low E0 to high E0 (compounds with high reduction potential are ready to accept electrons)
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Where does FADH2 deliver electrons to in the electron transport chain?
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Complex II (it carries two electrons to Complex II)
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Where does NADH deliver electrons to in the electron transport chain?
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Complex I (it carries one electron to Complex I)
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What are the electron acceptors in complex I, and what do they pass electrons to?
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FMN accepts electrons from NADH and passes to Fe-S, which ultimately delivers to Co Q
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What is the electron acceptor in Complex II, and what does they pass to?
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Fe-S accepts electrons, and ultimately delivers to Co Q
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What are the electron acceptors in Complex III, and where do they pass to?
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Cytochrome b, c1, and Fe-S accept electrons, and pass on to Cytochrome c
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What is another name for Complex IV?
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Cytochrome c oxidase
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What is the final electron acceptor?
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O2
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How are the Fe-S centers usually attached to proteins? How many Fe atoms can be contained?
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Fe-S centers are attached to proteins via cysteine residues, and contain 1-4 Fe atoms (non-heme Fe)
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What is the function of coenzyme Q in the electron transport chain? How many electrons can redox occur with at a time?
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Rate regulation of electron transport, delivering one electron at a time to complex III regardless if the source is NADH and FADH2
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What are the 3 cytochrome types? What iron structure do they contain?
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a, b, and c cytochromes contain protoporphyrin IX (heme ring)
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What are 3 inhibitors of electron transport?
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1) Antimycin A 2) Rotenone 3) Cyanide
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How does antimycin A inhibit electron transport?
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Inhibits enzyme cytochrome c reductase
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How does rotenone inhibit electron transport?
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Inhibits transfer of electrons from Fe-S in Complex I to Coenzyme Q, preventing NADH-based generation of ATP
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How does cyanide inhibit electron transport?
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Binds irreversibly to Fe in cytochrome oxidase (Complex IV), changing the shape of its active site
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How many ATP molecules can be synthesized per pair of electrons carried through the ETC?
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38
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What are other names for Complex V?
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ATP synthease, F1F0 complex
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What are the 2 components of ATP synthase? What is the function of each?
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1) F1 sphere- "knob-like" component located outside the membrane that synthesizes ATP 2) F0 stalk- portion of ATP synthase embedded in the membrane
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What are the 5 proteins that make up the F1 sphere of ATP synthase?
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Alpha, beta, delta, epsilon, and gamma
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How does oligomycin inhibit ATPase activity?
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It blocks the F0 subunit, preventing phosphorylation of ADP
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The orientation of what 2 F1 proteins determines the conformation of ATPase? Rotation of what F1 protein changes conformation?
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Alpha-beta subunit orientation determines conformation, and gamma subunit rotation alters their orientation
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What are the 3 conformations of the ATP synthase?
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1) Loose (L) 2) Tight (T) 3) Open (O)
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In ATP synthase, does the formation of ATP or rotation of the synthase require energy? Where does this energy come from?
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Formation of ATP is spontaneous and does not require energy, but rotation of the ATP synthase does require energy. The energy comes from the flow of protons through the F0 subunit, driven by their concentration gradient
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What is the sequence of ATP generation in ATP synthase, from ADP binding to release?
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ADP and Pi bind to the O conformation, and rotation switches to L conformation which holds the substrates. Another conformation converts to T conformation, triggering spontaneous ATP formation. A third and final rotation returns to O conformation, releasing ATP and allowing another ADP and Pi to bind http://en.wikipedia.org/wiki/ATP_synthase has a decent animation
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What is the chemiosmotic coupling that occurs in ATP production?
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The concentration gradient and flux of hydrogen ions is used to power the conformational turning of the ATP synthase
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How does dinitrophenol (DNP) affect oxidative phosphorylation?
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DNP uncouples electron transport/ATP synthesis by functioning as a proton transporter, disrupting the proton gradient to trigger the production of heat instead of ATP
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What are the uncoupling proteins' (UCP1, 2, 3) effect on ATP production and metabolism?
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They provide a proton channel to disrupt the electrochemical gradient, with the energy of the electron transport chain released as heat instead of synthesizing ATP. This increases metabolism as energy from food cannot be stored in cells
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What are 2 purposes for intentionally uncoupling oxidative phosphorylation?
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1) Cold - promotes UCP activity to generate heat and maintain body temperature 2) Excess food- increases UCP activity to convert some energy to heat instead of being stored
