OP oxidative Phosphorylase& ETC by Dedication.pptx electron transfer chain

oxidative Phosphorylase&electron transfer chain

1. Oxidative phosphorylation & Electron transport chain

2. contents Electron carriers Iron sulphur protein Cytochromes Proton motive force ATP synthase complex Uncouplers Inhibitors of energy transfer

3. Oxidative phosphorylation Introduction OP is culmination of energy yielding metabolism in aerobic organisms All oxidative stapes converge to final stage of cellular respiration, in which energy is converted into ATP PHOSPHORYLATION : “by which photosynthetic organisms capture the energy of sunlight to the ultimate source of energy in biosphere to make ATP”

4. Eukaryotes - OP – Mitochondria - Photophosphorylation – Chloroplast OP = Reduction 1. Reduction: O2 TO H2O (electron donate by NADH & FADH2) – light & dark Photophosphorylation = Oxidation Oxidation: H2O to O2 ( NADP+ Ultimate electron acceptor ) – absolutely depend on light energy This is only difference but fundamentally similar reaction

5. Chemiosmotic theory ATP synthesis in mitochondria & chloroplast is based on hypothesis given by Peter Mitchell in 1961 “The transmembrane differences in proton concentration are reservoir for energy extracted from various biological oxidation reaction”

6. The chemiosmotic mechanism for ATP synthesis.

7. OP & Photophosphorylation similarity 3 ways Involve flow of e through a chain of membrane bound carriers Free energy made by “downhill” electron flow coupled to “uphill” transport of proton- impermeable membrane, conserving free energy as a transmembrane electrochemical potential Flow of proton down their concentration gradient through sp. Protein channels provide free energy for ATP synthesis ( ATP Synthase couple proton to phosphorylation of ADP )

8. ELECTRON TRANSFER REACTION IN MITOCHONDRIA The discovery in 1948 by Eugene Kennedy and Albert Lehninger that mitochondria are the site of oxidative phosphorylation in eukaryotes . Albert L. Lehninger, 1917–1986

9. Selectively permeable

10. Electrons are funnelled to universal electron acceptors

11. Electrons are funnelled to universal electron acceptors

12. Electrons are funnelled to universal electron acceptors OP begins with entry of electron into respiratory chain Most of the electron arise from the action of dehydrogenases which collects electron from catabolic pathway and funnel them into universal e acceptors Nicotinamide nucleotide (NAD+ or NADP+) Flavin nucleotides (FAD)

13. Nicotinamide nucleotide – linked dehydrogenase (NAD + or NADP +) Catalyze reversible reaction generally as follows Most dehydrogenises are specific for NAD+ as an e acceptor

14. Nicotinamide nucleotide – linked dehydrogenase (NAD+ or NADP+) Medium NADH & NADPH are water soluble ē carriers Associated with reversibility with dehydrogenases NADH : carries ē from catabolic process to respiratory chain NADPH : supplies ē to anabolic process Maintain redox potential by holding the ratio of [reduced form]/[ oxidized form ] relatively high for NADPH and relatively low for NADH . Neither NADH nor NADPH can cross the inner mitochondrial membrane, but the electrons they carry can be shuttled across indirectly

15. Flavoproteins (FMN or FAD) The FMN and FAD molecules are tightly or covalently linked to flavoproteins .( to the active site) The reduction potential of these molecules depends on the interactions with local sites on the protein. Unlike NAD or NADP molecule, can accept one or two electrons , depends on protein with it is associated thus : FMN/FAD + e⁻ FMNH + /FADH+ OR FMN/FAD + 2e⁻ FMNH ₂/FADH₂

16. E carriers The mitochondrial respiratory chain consists of a series of sequentially acting electron carriers , most of which are integral proteins with prosthetic groups capable of accepting and donating either one or two electrons. Three types of electron transfers occur in oxidative phosphorylation: ( 1) direct transfer of electrons, as in the reduction of Fe3 to Fe2; ( 2) transfer as a hydrogen atom ( H + e ); and (3) transfer as a hydride ion ( : H), which bears two electrons. The term reducing equivalent is used to designate a single electron equivalent transferred in an oxidation-reduction reaction.

17. In addition to NAD and flavoproteins, three other types of electron-carrying molecules function in the respiratory Chain: A hydrophobic quinone (ubiquinone) and Iron-containing proteins (cytochromes) 3. Iron-containing proteins (iron-sulfur proteins). Ubiquinone (also called coenzyme Q, or simply Q) is a lipid-soluble benzoquinone

18. Ubiquinone Ubiquinone (also called coenzyme Q, or simply Q) is a lipid-soluble benzoquinone With long isoprenoide side chain In plant- plastoquinone Bacteria- menaquinone carrying e in membrane associated ETC Act as junction between 2 e donor and 1 e acceptor Because its very small & hydrophobic, is freely diffusible with in lipid bilayer of inner mitocho. Membrane Shuttle reducing equivalent between other less mobile e carriers in membrane It plays central role in coupling electron flow to proton movement because it carries both proton & electrons

19. Cytochrome Proteins with characteristics strong absorption of visible light, due to their iron containing heme prosthetic group Mitochondria contain 3 class of cytochromes ; a, b & c , distinguished on basis of light absorption spectra In reduced form its have 3 absorption band in visible range Heme cofactor of a & b non covalently bound to associated protein In cytochrome c its covalently attached through cys residue

20. Iron sulfur protiens 1 st discovered by Helmut Beinurt Fe is not present in heme but present in association with sulphur atoms or sulfur of cys residue in protein , or both Fe-S centre ranges from simple structure with single Fe atom coordinated to 4 Cyst -SH group to more complex Fe-S centres with two to four Fe atoms Rieske iron- sulfur protein is one variation of this protien Fe bound to S of 2 His in place of 2 Cys . All Fe-S protein participate in only 1 ē transfer in which 1 Fe atom of Fe-S is oxidized or reduced. At least 8 Fe-S proteins functions in mitochondrial ē transport

21. Iron sulphur protiens

22. Overall reaction catalyzed by mitochondrial respiratory chain ē moves from NADH or Succinate or flavoproteins → Q →Fe-S protien  cytochrome b → cytochrome c1 → cytochrome c → cytochrome a → cytochrome a3 → O2

23. Electron Carriers Function in Multienzyme Complexes The electron carriers of the respiratory chain are organized into membrane- embedded supramolecular complexes that can be physically separated. Gentle treatment of the inner mitochondrial membrane with detergents allows the resolution of 4 unique electron carrier complexes, each capable of catalyzing electron transfer through a portion of the chain . Complexes I catalyze electron transfer from electron donors NADH to ubiquinone Complexes II catalyze electron transfer from succinate to ubiquinone Complex III carries electrons from reduced ubiquinone to cytochrome c , and Complex IV completes the sequence by transferring electrons from cytochrome c to O2.

24. Relationship between complex – l & complex - ll

25. Complex I: NADH to Ubiquinone Complex I, also called NADH:ubiquinone oxidoreductase or NADH dehydrogenase, Is a large enzyme composed of 42 different polypeptide chains, Including an FMN -containing flavoprotein Include six iron sulfur centers. High resolution electron microscopy : L shaped have 2 arm - one arm in membrane - second arm extending into matrix Complex I catalyzes two simultaneous and obligatory coupled processes: (1) the exergonic transfer of a hydride ion from NADH and a proton from the matrix to ubiquinon (2) the endergonic transfer of four protons from the matrix to the intermembrane space .

26. Complex I is therefore a proton pump driven by the energy of electron transfer . the reaction it catalyzes is vectorial : it moves protons in a specific direction from one location (the matrix, which becomes negatively charged with the departure of protons) to another (the intermembrane space, which becomes positively charged).

27. Complex II: Succinate to Ubiquinone Also known as succinate dehydrogenase, the only membrane-bound enzyme in the citric acid cycle Smaller & simpler than complex –l 5 prosthetic group of 2 types 4 different protein subunits : A,B,C & D A & B extended into matrix B contain three 2 Fe-S A bound to FAD & binding site for succinate C & D integral membrane protein 3 transmembrane helices contain heme group ( heme b) - binding site for Ubiquinone

28. Complex II: Succinate to Ubiquinone The heme b is not on the main path of electron transfer but protects against the formation of reactive oxygen species (ROS) by electrons that go astray Mutation in complex- ll gene cause hereditary PARAGANGLIOMA Maintain – high production of ROS cause greater tissue damage

29. Other substrate for mitochondrial dehydrogenases Pass ē to respiratory chain at ubiquinon but not through complex - l & - ll 1 st step in B- oxidation of fatty acyl - CoA Transfer ē Flavoprotein ( acyl CoA dehydrogenases ) FAD ubiquinone : ETC Transfer ē ETF : Ubiquinone oxidoreductase

30. Complex III: Ubiquinone to Cytochrome c The next respiratory complex, Complex III, also called cytochrome bc1 complex or ubiquinone:cytochrome oxidoreductase , transfer of electrons from ubiquinol (QH2) to cytochrome c with the vectorial transport of protons from the matrix to the intermembrane space.

31. Complex III: Ubiquinone to Cytochrome c Dimer of two identical monomer Monomer contain 11 different subunits From this only 3 subunits are functional core 1 st sub unit – cytochrome b : contain 2 heme b centre 2 nd sub unit – Riske iron-sulfur protien : contain 2Fe-2S centre 3 rd subunit – cytochrome C1 : contain heme c center

32. The Q cycle Q cycle accommodates switch between 2 ē carrier Ubiquinon to 1 ē carrier cytochrome b & c Though pathway is complex but net effect of transfer is simple :QH2 (reduced) is oxidized to Q & 2 mol of cytochrome C (reduced) Cytochrome C is soluble protein – intermembrane space After single heme c group accept ē from complex – lll moves to complex –IV where it donate ē to binuclear Cu center

33. Complex IV: Cytochrome c to O2 Cytochrome c to O2 Is the final step of the respiratory chain, Complex IV, also called cytochrome oxidase , carries electrons from cytochrome c to molecular oxygen , reducing it to H2O

34. Large enzyme – eukaryotes contain 13 subunits Bacteria contain only 3 Present in inner mitochondrial membrane So only 3 is critical for functioning Subunit- ll contain 2 Cu ion complexd with – SH group of Cys make binuclear center subunit - l contain 2 heme group designated heme a & Cu B - binuclear center subunit – iii contain heme a3

35. Arrangement of Complexes of ETS