Transport ph 075

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Unformatted text preview: /1978 Artificially introduce proton/electrical gradient. What happens? ΔG ≈ 0 for ATP formation by ATP Synthase ATP Hydrolysis: ≈ 10 s ­1 ATP Synthesis: ≈ 24 s ­1 Keq = 2.4** What is ΔG°’? ** Error!! Should be: Keq = 10 s ­1/24 s ­1 = 0.42 Aside: the Art of the Estimate ΔG°’ =  ­RT ln Keq =  ­(8.31 kJ/mol•T) (298 K) (2.3) log Keq ~  ­(6 kJ/mol) log 2.4 ~  ­2 kJ/mol Energy is Required to Release Product How is this energy supplied? Proton Flow is Used for ATP Release by ATP Synthase Does Tight Product Binding Supply Sufficient Energy for ATP Synthesis? Kd (ADP) ≈ 10 ­5 M Kd (ATP) ≈ 10 ­12 M ΔG1°’ =  ­RT ln 10 ­5 ΔG2°’ =  ­RT ln 10 ­12 ΔΔG°’ = ΔG1°’ – ΔG2°’ ~  ­(6 kJ/mol) (log 10 ­5 – log 10 ­12) ~  ­(6 kJ/mol) (7) ~  ­42 kJ/mol ΔG°’ (ATP hydrolysis) =  ­30.5 kJ/mol Proposed Transition-State Complex Testing the ATP Synthase Mechanism A Single Molecule Experiment http://www.k2.phys.waseda.ac.jp/ F1movies/F1Prop.htm Noji et al. (1997) Nature 386:299-302. Fo/F1 Complex Also Rotates Note: ATP hydrolysis Rate of Rotation Can be Determined (133 ms/Frame) Note Discrete Jumps Final Step: Shipping ATP to the Cytosol Membrane Poten9al Assists Form a complex in vivo? (ATP synthasome) Proton ­Mo9ve Force Assists Odds & Ends: Malate-Aspartate Shuttle NAD+/NADH cannot cross the inner mitochondrial membrane. How is NADH from glycolysis used? •  Oxaloacetate is reduced to malate by cytosolic malate dehydrogenase •  Malate enters mitochondria and is oxidized to oxaloacetate by mitochondrial malate dehydrogenase •  Note: oxaloacetate is deaminated Asp α ­ketoglutarat is deaminated Glu •  Carbon balance is maintained by Asp/Glu transport and swapping amine groups Malate-Aspartate Shuttle (don’t memorize) Rogue Electrons: Reactive Oxygen Species (ROS) SOD: 2O2— + 2H+  H2O2 + O2 Catalase: 2H2O2  2H2O + O2 GSH: 1 ­10 mM Glutathione Reductase: Similar to E3 in Pyruvate Dehydrogenase (but runs in the opposite direc9on) Eastern Skunk Cabbage Oxidizing Ubiquinol Without Pumping Hydrogen Generates Heat in Some Plants An uncoupling protein in brown fat similarly provides heat for babies and during hiberna1on Additional Study Questions •  Be able to describe the key features of oxida9ve phosphoryla9on and the proteins involved •  Describe what might happen to overall energy use if each of the proteins were mutated and no longer func9onal •  Describe how the cofactors we have seen func9on •  Suggest what might happen if each were missing •  The first 25 ques9ons at the back of the chapter loosely relate to our material – have a look at these. •  More to come...
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