1. Lecture 13 Electron Transport

2. Reduced High energy Oxidized Low energy Glucose + 02---  CO2 + H20

4. Mitochondria

5. The pumps

6. Overview electron transport Working of respiratory chain is different from enzymatic reactions where energy is passed down from one energy rich bond to another. Here chemical reaction is coupled to physical force. 1separation of protons and electrons of hydrogen 2Passage of electrons down cascade-four membrane protein complexes (proton pumps expel protons) 3Electrons travel down chain and are picked up by oxygen and combine with proton forming H2O 4Proton accumulate outside mito and are pumped back through inner membrane-mol motor rotates by flow of protons driving synthesis of ATP from ADP+Pi ADPATP

7. Summary 1Complex1 accepts H+ from NADH2 converting it back to NAD. Electrons are transferred to carrier-ubiquinone. 2 Hydrogen protons + 2 additional protons are expelled/electron (Free energy of electron transfer is used) 2Complex2 accepts hydrogen from succinate and transfers electrons to ubiquinone (CoenzyQ) 3Complex3 re-oxidizes CoenzyQ and expels four protons/electron. Electrons are transferred to carrier CytochromeC (Free energy of electron transfer is used to expel proton). 4Complex4 re-oxidizes CytC and electrons are transferred to oxygen. Free energy of electron transfer is used to expel 4 protons

8. Electrons do not occur in free form. Proteins provide grps that bind and release electrons. These are in close physical proximity. Successive transfer of electrons must be exergonic- free energy must be negative Cofactors that bind/release electrons 1Flavins 2Iron-sulfur cluster (Fe held by 4 sulfur) 3Porphyrin (heme- Fe2+ to Fe3+) 4Copper ions Two electron carriers are mobile AUbiquinone (CoenzymeQ)- carries electrons as hydrogen and moves within inner membrane. Transports electrons from complex1 and 2 to complex3 BCytochromeC (contains Heme) located between inner and outer membrane. Transports electrons from complex3 tocomplex4

9. Std reduction potential Free energy of electron movement from one cofactor to next must be negative. Cofactors down the chain have higher affinity for electrons- they have higher redox potential. Redox Carrier  E 0 ’ NAD+-0.32V FMN (complex1)-0.30V Fe-S (complex1)-0.03V FAD (complex2)-0.04V Ubiquinone (carrier)0.04V Heme (complex3)0.235V CytochromeC (carrier)0.25V Heme (complex4)0.38V Oxygen0.82V

10. Complex 1-4

11. The gradient

12. Path of electrons Electrons are stripped of their protons, the protons are released at cytosolic side. This accounts for some of the proton translocation. The mechanism by which the additional protons are expelled from the mitochondria is not known. Possible that binding and release of electrons causes conformational changes in protein complexes (analogous to allosteric change) and these may help expel protons.

13. Path of electrons 1-2

14. Path of electrons 3

15. Path of electrons 4

16. Protonmotive force Cytosol Mitochondrial matrix ATP is synthesized AFTER substrate is vanished in form of CO2 and H2O. The energy is stored in PROTON MOTIVE force. Proton conc in cytosol is 10 times higher than in mitochondrial matrix. Proton moving down the gradient generates free energy (6kJ/mol) Each proton ejected leaves one negative charge inside mitochondria- generates electrostatic membrane potential- 150mV negative inside=15kJ/mol Total protonmotive force is 21kJ/mol

17. H+ pump

18. ATP synthase Mito matrix Cytoplasm

19. 1Protons flow between a and F 0 subunit (with 10 c chains). 2This causes F 0 subunit to rotate (aspartate in c chain in F 0 interacts with proton and undergo conformational change resulting in rotation). The proton is translocated and released into mitochondrial matrix 3  subunit rubs against  hexamer  hexamer that rub undergo conformational change  subunit contains active site that binds ADP+Pi  subunit utilizes energy transmitted from conformational change to synthesize ATP  subunit gets everted and ATP is released.

20. ADP to ATP

21. ATP transport