BIOENERGETICSYulia Suciati

Krebs Cycle, Electron Transport and Oxidative Phosphorylation

Yulia Suciati

SIKLUS KREBS

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.

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:

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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• 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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• 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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• Step 5: Substrate-Level Phosphorylation

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• Step 6: Flavin-Dependent Dehydrogenation

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• Step 7: Hydration of a Carbon-Carbon Double Bond

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• Step 8: A Dehydrogenation Reaction that will Regenerate Oxaloacetate

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.

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

FOSFORILASI OKSIDATIF

The figure is found at http://plaza.ufl.edu/tmullins/BCH3023/cell%20respiration.html (December 2006)

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

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 from matrix

Succinate-CoQ oxidoreductase (complex II)

• Succinate-CoQ oxidoreductase– succinate dehydrogenase is a component– No protons transported– FAD, FeS serve as intermediate electron

carriers

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 deposited in intermembrane space, 1 e- to Cyt c, 1 e- to Qn

• Qn with 2 e- takes 2 H+ from matrix.

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 occursin matrix, thus removing 4 H+

Chemiosmosis

• Chemiosmosis - Movement of protons from high (IMS) to low conc (matrix) used to drive ATP synthesis

• electrochemical gradient - electrical and chemical potential• Electron transport drives generation of H+ gradient

– +0.14V electrical potential– 1.4 pH unit difference– G=~21 kJ/mole H+

• H+ gradient drives ATP synthesis

The figure is found at http://plaza.ufl.edu/tmullins/BCH3023/cell%20respiration.html (December 2006)

ATP synthase

inner mitochondrial membrane

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

small molecule shuttles

• molecules must be transported to and from matrix

• ATP-ADP translocase exports ATP, imports ADP - movement of more negative ATP from matrix dissipates 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

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 ATPper pair of electrons)

Malate – Aspartate Shuttle

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

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

Inhibitors

• Electron flow can be inhibited by POISONS

• Useful in lab to control entry and exit points for electron transport studies

• Proton gradients are dissipated by DNP & FCCP, inhibiting ATP synthesis

• Thermogenin in “brown adipose tissue” dissipates proton gradient togenerate heat

The figure is found at http://departments.oxy.edu/biology/Franck/Bio222/Lectures/March23_lecture_shuttles.htm (December 2006)

Uncoupling proteins

(UCP)

= separate RCH from

ATP synthesis

(the synthesis is interrupted)

energy from H+ gradient is

released as a heat

SEMOGA BERMANFAATYS 2011