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1 Objectives 1.To know about the structural and biochemical organizations of a mitochondrion 2.To understand the electrochemical reactions through which.

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Presentation on theme: "1 Objectives 1.To know about the structural and biochemical organizations of a mitochondrion 2.To understand the electrochemical reactions through which."— Presentation transcript:

1 1 Objectives 1.To know about the structural and biochemical organizations of a mitochondrion 2.To understand the electrochemical reactions through which the chemical energy in food can be converted to chemical energy in ATP 3.To realize how the structural organizations of mitochondria have allowed the above electrochemical reactions to be carried out effectively

2 2 Energy Conversion (1): Mitochondria Cellular respirationCellular respiration -Flow of electrons from reduced coenzymes to an electron acceptor; generation of ATP -NADH and FADH 2 from glycolysis, TCA cycle,  - oxidations, etc. -Ultimate electron acceptor is oxygen; reduced form as water (aerobic respiration); takes place with mitochondria in eukaryotic cells

3 3 The Energy Powerhouse Discrete sausage-shaped structures; the second largest organelle in most animal cellsDiscrete sausage-shaped structures; the second largest organelle in most animal cells A double-membrane organelle; outer membrane separated from inner membrane by intermembrane spaceA double-membrane organelle; outer membrane separated from inner membrane by intermembrane space A.Outer membrane Not a significant permeability barrier for ions and small molecules; transmembrane proteins (porins)Not a significant permeability barrier for ions and small molecules; transmembrane proteins (porins)

4 4 B.Intermembrane space Continuous with the cytosolContinuous with the cytosol C.Inner membrane A permeability barrier to most solutesA permeability barrier to most solutes Locale of the protein complexes of electron transport and ATP synthesisLocale of the protein complexes of electron transport and ATP synthesis Distinctive foldings (cristae); increase surface area to accommodate more the protein complexesDistinctive foldings (cristae); increase surface area to accommodate more the protein complexes

5 5 D.Matrix Semi-fluid enclosed by inner membrane;Semi-fluid enclosed by inner membrane; -Enzymes for mitochondrial functions -A circular DNA molecule; coding for its own rRNAs, tRNAs, and a number of polypeptide subunits of inner-membrane proteins (genetic competence)

6 6 Electron Transport System (ETS) Transfer of electrons from NADH and FADH 2 is highly exergonicTransfer of electrons from NADH and FADH 2 is highly exergonic Multistep process; a series of reversibly oxidizable electron carriers; total free energy difference is released in increments to prevent excessive amount being released as heat (energy conservation for ATP)Multistep process; a series of reversibly oxidizable electron carriers; total free energy difference is released in increments to prevent excessive amount being released as heat (energy conservation for ATP) 4 different kinds of carriers::4 different kinds of carriers::

7 7 A.Flavoproteins Membrane-bound proteins using either flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN) as prosthetic groupMembrane-bound proteins using either flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN) as prosthetic group Transfer both electrons and protonsTransfer both electrons and protons

8 8 B.Iron-Sulfur Proteins Proteins containing iron-sulfur (Fe/S) centers; iron and sulfur atoms complexed with cysteine groups of the proteinProteins containing iron-sulfur (Fe/S) centers; iron and sulfur atoms complexed with cysteine groups of the protein Alternates between the Fe 3+ (ferric) and Fe 2+ (ferrous)Alternates between the Fe 3+ (ferric) and Fe 2+ (ferrous) Do not pick up and release protonsDo not pick up and release protons C.Cytochromes (Cyt) Contain iron; part of a porphyrin prosthetic group (heme)Contain iron; part of a porphyrin prosthetic group (heme)

9 9 One-electron carriers; transfer electrons only:One-electron carriers; transfer electrons only: 1.Cyt b, c 1, a and a 3 are integral membrane proteins 2.Cyt c is relatively hydrophilic; loosely associated with inner face of membrane; not a part of the complexes; mobile electron carrier

10 10 3.Cyt a and a 3 Copper - containing - cytochromes (bimetallic iron-copper (Fe/Cu) center)Copper - containing - cytochromes (bimetallic iron-copper (Fe/Cu) center) Components of cytochrome c oxidaseComponents of cytochrome c oxidase Keeping an O 2 molecule bound to the oxidase complex; completely picked up the four electrons and four protonsKeeping an O 2 molecule bound to the oxidase complex; completely picked up the four electrons and four protons

11 11 D.Coenzyme Q (CoQ) Ubiquinone (a benzene derivative); the only nonprotein componentUbiquinone (a benzene derivative); the only nonprotein component Carries both protons and electronsCarries both protons and electrons Not part of a respiratory complex; a collection point for electrons from FMN- and FAD-linked dehydrogenasesNot part of a respiratory complex; a collection point for electrons from FMN- and FAD-linked dehydrogenases Active transport of protons across inner mitochondrial membraneActive transport of protons across inner mitochondrial membrane

12 12 The electron carriers function in a sequence determined by their relative reducing power (reduction potentials)The electron carriers function in a sequence determined by their relative reducing power (reduction potentials) -Two interconvertible molecules or ions by the loss or gain of electrons (redox pair) With exceptions of CoQ and Cyt c, the electron carriers are organized into four large multiprotein complexes (respiratory complexes)With exceptions of CoQ and Cyt c, the electron carriers are organized into four large multiprotein complexes (respiratory complexes)

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14 14 A.Complex I NADH-coenzyme Q oxidoreductaseNADH-coenzyme Q oxidoreductase -Transfers electrons from NADH to coenzyme Q B.Complex II Succinate-coenzyme Q oxidoreductaseSuccinate-coenzyme Q oxidoreductase -Transfers electrons derived from succinate oxidation in TCA

15 15 C.Complex III Coenzyme Q – cytochrome c oxidoreductaseCoenzyme Q – cytochrome c oxidoreductase -Accepts electrons from coenzyme Q and passes them to cytochrome c D.Complex IV Cytochrome c oxidaseCytochrome c oxidase -A terminal oxidase; capable of direct transfer of electrons to oxygen

16 16 Respiratory Complex Electron Flow NumberName Number of Polypeptides Prosthetic Groups Accepted from Passed to Proton Transport ? I NADH dehydrogenase (NADH-coenzyme Q oxidoreductase) FMN 6-9 Fe/S centers NADH Coenzyme Q Yes II Succinate-coenzyme Q oxidoreductase (succinate dehydrogenase) FAD 3 Fe/S centers Succinate (via enzyme-bound FAD) Coenzyme Q No III -cytochrome c oxidoreductase (cytochrome b-c 1 complex) cytochrome b 1 cytochrome c 1 1 Fe/S center Coenzyme Q Cytochrome c Yes IV Cytochrome c oxidase 9 1 cytochrome a 1 cytochrome a 3 2 Cu centers (as Fe/Cu centers with cytochrome a 3 ) Cytochrome c Oxygen (O 2 ) Yes Properties of the Mitochondrial Respiratory Complexes

17 17 ATP Generation / Electron Transport ATP generation: ADP + Pi  ATPATP generation: ADP + Pi  ATP A.Photophosphorylation B.Substrate level phosphorylation Glycolysis: 1,3-bisphosphoglycerate  3- phospho-glycerate; phosphoenolpyruvate  pyruvateGlycolysis: 1,3-bisphosphoglycerate  3- phospho-glycerate; phosphoenolpyruvate  pyruvate TCA: succinyl CoA  succinateTCA: succinyl CoA  succinate -4 ATP molecules/glucose: 2 from glycolysis + 2 from TCA

18 18 C.Oxidative phosphorylation 6 different oxidations (12 pairs of electrons):6 different oxidations (12 pairs of electrons): 1.Glycolysis: glyceraldehyde-3-phosphate  1,3- bisphosphoglycerate (+NADH) 2.Pyruvate  acetyl CoA (+NADH) 3.TCA: isocitrate   -ketoglutarate (+NADH);  - KG  succinyl CoA (+NADH); succinate  fumarate (+FADH 2 ); malate  oxaloacetate (+NADH)

19 19 Chemiosmotic Model Electrochemical potential across a membrane; the link between electron transport and ATP formationElectrochemical potential across a membrane; the link between electron transport and ATP formation -Exergonic transfer of electrons between and within respiratory complexes; unidirectional pumping of protons across the membrane where the transport system is localized

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21 21 The F 0 F 1 Complex A F-type ATPase; both ATPase and ATP synthase activitiesA F-type ATPase; both ATPase and ATP synthase activities Converts electrochemical energy (proton gradient) into potential chemical energy (ATP)Converts electrochemical energy (proton gradient) into potential chemical energy (ATP) A.F 1 complex 3  and 3  polypeptides; 3  complexes (catalytic hexagon)3  and 3  polypeptides; 3  complexes (catalytic hexagon)

22 22 -  subunit: catalytic site for ATP synthesis/hydrolysis;  subunit: ATP/ADP- binding site Both ATP synthase and ATPase activitiesBoth ATP synthase and ATPase activities Proton translocation through F 0 drives ATP synthesis by F 1Proton translocation through F 0 drives ATP synthesis by F 1 B.Stalk Composes of ,  and  subunitsComposes of ,  and  subunits Allows rotation of F 1 complex about F 0 complexAllows rotation of F 1 complex about F 0 complex

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24 24 C.F 0 complex Consists of 1a, 2b and 9-12 c subunitsConsists of 1a, 2b and 9-12 c subunits c subunits are organized in a circle; proton channelc subunits are organized in a circle; proton channel As a proton translocator: channel through which protons flowAs a proton translocator: channel through which protons flow (protonation and deprotonation of aspartate)

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26 26 Binding Change Model To explain how exergonic flow of protons through F 0 can drive endergonic phosphorylation of ADP to ATPTo explain how exergonic flow of protons through F 0 can drive endergonic phosphorylation of ADP to ATP Electrochemical–to–mechanical–to–chemical transducerElectrochemical–to–mechanical–to–chemical transducer Each of the three  subunits exists in 3 different conformations at any point in time:Each of the three  subunits exists in 3 different conformations at any point in time:

27 27 -(O)pen: little affinity; ADP and Pi are free to enter (ATP is free to leave) the catalytic site -(L)oose: higher affinity; lose binding of ADP and Pi -(T)ight: Packing the ADP and Pi together tightly; facilitating the condensation -O  L  T:

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29 29 1.Flowing of protons flow through a channel in the a subunit of F 0 2.Rotation of the ring of c subunits; rotation of the attached  subunit 3.Asymmetry of the  subunit; different interactions with the three  subunits at any point in time 4.Each  subunit passes successively through the O, L, and T conformations as the  subunit rotates 360º

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