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    Krebs Cycle, Electron Transport

    and Oxidative Phosphorylation

    Yulia Suciati

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    SIKLUS KREBS

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    SIKLUS ASAM SITRAT

    Terjadi didalam matriks mitokondria

    Proses ini bersifat aerobik

    Fungsi utama siklus asam sitrat (siklus krebs)a/ bekerja sbg lintasan akhir bersama untuk

    oksidasi KH, Lipid, Protein.

    Glukosa, as. Lemak, AA, dimetab. Mjd asetil

    KoA atau senyawa antara di SAS.

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    SIKLUS ASAM SITRAT

    Step 1: Condensation

    In step 1 of the Krebs cycle, the two-carbon

    compound, acetyl-S-CoA, participates in a

    condensation reaction with the four-carbon

    compound, oxaloacetate, to produce citrate:

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    SIKLUS ASAM SITRAT

    Step 2. Isomerization of Citrate

    step 2 involves moving the hydroxyl group in the

    citrate molecule so that we can later form an

    a-keto acid

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    SIKLUS ASAM SITRAT

    Step 3: Generation of CO2 by an NAD+ linked

    enzyme

    The Krebs cycle contains two oxidative

    decarboxylation steps; this is the first one

    The reaction is catalyzed by the enzyme

    Isocitrate dehydrogenase

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    SIKLUS ASAM SITRAT

    Step 4: A Second Oxidative Decarboxylation

    Step

    This step is performed by a multi-enzyme

    complex, the a-Ketoglutarate

    Dehydrogenation Complex

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    SIKLUS ASAM SITRAT

    Step 5: Substrate-Level Phosphorylation

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    SIKLUS ASAM SITRAT

    Step 6: Flavin-Dependent Dehydrogenation

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    SIKLUS ASAM SITRAT

    Step 7: Hydration of a Carbon-Carbon Double

    Bond

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    SIKLUS ASAM SITRAT

    Step 8: A Dehydrogenation Reaction that will

    Regenerate Oxaloacetate

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    HASIL AKHIR S.A.S

    12 molekul ATP terbentuk pada setiap kali

    putaran S.A.S

    Sejumlah ekuivalen pereduksi akan dialihkan

    kpd rantai pernafasan dlm membran dalam

    mitokondria.

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    VITAMIN YG PENTING PD S.A.S

    Riboflavin, dlm bentuk FAD (Flavin Adenin

    Dinukleotida)

    Niasin, dlm bentuk NAD (Nikotinamide

    Dinukleotida)

    Tiamin, dlm bentuk TPP (Tiamin Pirophosfat)

    Asam pantotenat, sbg bag. dr Koenzim A

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    FOSFORILASI OKSIDATIF

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    Electron Transport Complexes

    4 multiprotein complexes in mitochondrial IM

    NADH-CoQ (ubiquinone) oxidoreductase

    Succinate-CoQ oxidoreductase

    Ubiquinone-cytochrome c oxidoreductase Cytochrome c oxidase - reduction of O2

    Contain a variety of prosthetic groups, iron-sulfur clusters

    Some subunits encoded by mitochondrial DNA

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    NADH-CoQ (ubiquinone) oxidoreductase (complex I)

    2 electrons passed from NADH, through

    FMN, FeS intermediate electron carriers to

    ubiquinone (coenzyme Q)

    Ubiquinone - lipid soluble electron carrier

    Proton pumps transport 4 H+ from matrix to

    intermembrane space per pair of electrons

    Spatial organization important - protons

    used in reduction of ubiquinone come frommatrix

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    Succinate-CoQ oxidoreductase (complex II)

    Succinate-CoQ oxidoreductase

    succinate dehydrogenase is a component

    No protons transported

    FAD, FeS serve as intermediate electron

    carriers

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    Ubiquinone-cytochrome c

    oxidoreductase (complex III)

    Cytochrome c - peripheral protein,

    electron carrier

    Cytochromes can only accept 1

    electron at a time, resulting in Q cycle 2 H+ from 1st Q deposited in

    intermembrane space,

    1 e- to Cyt c, 1 e- to Qn

    2 H+ from 2nd Q depositedin intermembrane space,

    1 e- to Cyt c, 1 e- to Qn

    Qn with 2 e- takes 2 H+

    from matrix.

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    Cytochrome c

    oxidase

    catalyzes reduction of

    molecular oxygen

    13 subunits

    Four protons translocated for

    each O2 reduced

    Accumulates 4 electrons (Cu+, Fe2+) for

    complete reduction before releasing products

    or toxic partially-reduced products

    O2 + 4 e- + 4 H+ --> 2 H2O occurs

    in matrix, thus removing 4 H+

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    ATP Synthase

    ATP Synthase produces ATP

    from ADP & Pi

    H+ passage causes conformational changes

    (rotation) in F1, leading to release of ATP so

    ADP can bind again

    about 3 protons per ATP must pass

    through ATP synthase

    The Big Picture

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    The Big Picture

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    small molecule shuttles

    molecules must be transported to and

    from matrix

    ATP-ADP translocase exports ATP, imports ADP -

    movement of more negative ATP from matrixdissipates electrical potential across membrane,

    weakening gradient by 1 H+.

    Phosphate translocase uses 1 H+.

    cytosolic NADH

    DHAP is reduced by NADH to

    Glycerol-3-P in muscle

    Electrons passed through FAD to Q

    is less efficient, but allows transport

    against large NADH gradient

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    malate-aspartate shuttle

    malate-aspartate shuttle used in heart, liver, kidney to

    transfer cytosolic reducing equivalents to matrix

    No loss in ATP

    generation (2.5 ATP

    per pair of electrons)

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    Malate Aspartate Shuttle

    http://courses.cm.utexas.edu/emarcotte/ch339k/fall2005/Lecture-Ch19-2/Slide14.JPG

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    ATP yield/glucose

    2 ATP - Glycolysis

    3-5 ATP from 2 FADH from 2 NADH from glycolysis

    5 ATP from 2 NADH from transition reaction 15 ATP from 6 NADH from TCA cycle

    2 ATP from 2 GTP from TCA cycle

    3 ATP from 2 FADH from TCA cycle

    30-32 ATP from complete oxidation of glucose

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    Inhibitors

    Electron flow can be inhibited by

    POISONS

    Useful in lab to control entry and

    exit points for electron transportstudies

    Proton gradients are dissipated by

    DNP & FCCP, inhibiting ATP

    synthesis Thermogenin in brown adipose

    tissue dissipates proton gradient

    to

    generate heat

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    SEMOGA BERMANFAATYS 2010