Electron transport and oxidative phosphorylation
Electron transport and oxidative phosphorylation
≈ 140 mV
≈ 60 mV
≈ 200 mV ≈ kBT pro H+
Electron transport in mitochondria is coupled to protontranslocation
Electron transport and oxidative phosphorylation
• Most of the free energy released during oxidation of glucose to CO2 is retained inNADH
• During respiration, electrons are released from NADH and eventually aretransferred to O2 (forming H2O)
• The step-by-step transfer of electrons via the electron transport chain allows thelarge amount of free energy produced by the transfer of electrons to O2 to bereleased in small increments
• Several electron transport chain components convert these small increments intoa proton and voltage gradient across the inner membrane
• The movement of protons down their electrochemical gradient drives thesynthesis of ATP from ADP and Pi
Electron transport and oxidative phosphorylation
≈ 800 kD22 proteins
≈ 500 kD8 proteins
≈ 300 kD9 proteins
The stepwise flow of electrons through the electrontransport chainThe redox potential increases aselectrons flow down the respiratorychain to oxygen. The standard free-energy change, for the transfer of thetwo electrons donated by an NADHmolecule can be obtained from theright-hand ordinate. Electrons flowthrough an enzyme complex by passingin sequence to the four or more electroncarriers in each complex. As indicated,part of the favorable free-energy changeis harnessed by each enzyme complexto pump H+ across the mitochondrialinner membrane. Although the numberof H+pumped per electron (n) isuncertain, it is estimated that theNADH dehydrogenase and b-c1complexes each pump two H+ perelectron, whereas the cytochromeoxidase complex pumps one.The twoelectrons transported from FADH2,generated by fatty acid oxidation and bythe citric acid cycle (see Figure 14-14),are passed directly to ubiquinone, andthey therefore cause less H+ pumpingthan the two electrons transported fromNADH (not shown).
The pathway of electron transport and proton transport inthe inner mitochondrial membrane
3 independent complexes with mobile carriers
The proton-motive Q cycle
Three-dimensional structures of some iron-sulfur clusters in electron-transporting proteins
Heme prosthetic groups of respiratory- chain cytochromesin mitochondria
Fe II <--> FeIII
Cytochrome C
Heme group
Coenzyme Q is theonly electron carrierthat is not a protein-bound prostheticgroup
The multiprotein complexes and associated prostheticgroups of the mitochondrial electron transport chain
Coupling of H+ pumpingand O2 reduction bycytochrome c oxidase
Molecular structure of the core of cytochrome c oxidase
Molecular structure of thecore of cytochrome c oxidase
Oxidation of reduced cytochrome c by cytochrome coxidase is coupled to proton transport
Electron transport and oxidative phosphorylation
Localizing and Manipulating Individual Bactriorhodopsins in a Purple Membrane
Oesterhelt, F.; Oesterhelt, D.; Pfeiffer, M.; Engel, A.; Gaub, H. E.; Müller, D. J. Science 2000, 288, 143-
Experiments withmembrane vesicles supportthe chemiosmoticmechanism of ATPformation
ATP synthase comprises aproton channel (F0) andATPase (F1)
Electron transport and oxidative phosphorylation
An experiment demonstratingthat the ATP synthase is drivenby proton flow. By combining alight-driven bacterialprotonpump (bacteriorhodopsin), anATP synthase purified from oxheart mitochondria, andphospholipids, vesicles wereproduced that synthesizedATP in response to light.
Mitochondrial F1 particles are required for ATP synthesisbut not for electron transport
Demonstration that the γsubunit of F0 rotatesrelative to the (αβ)3hexamer in an energy-requiring step
The F0F1 complex harnesses the proton-motive force topower ATP synthesis
Transporters in theinner mitochondrialmembrane are poweredby the proton-motiveforce
Rate of mitochondrialoxidation depends on ADP levels =respiratory control
Cytosolic enzymes convert glucose to pyruvate (steps 1-3)
The ATP Synthase can work reverse
Beispiel:Michaelis-MentenKinetik der F1-Atpase
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