Chapter 14 electron transport and oxidative phosphorylation
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Chapter 14 - Electron Transport and Oxidative Phosphorylation. The cheetah, whose capacity for aerobic metabolism makes it one of the fastest animals. Oxidative Phosphorylation in Mitochondria. Oxidative phosphorylation is the process by which NADH and FADH 2 are oxidized and ATP is formed

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Chapter 14 - Electron Transport and Oxidative Phosphorylation

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Chapter 14 electron transport and oxidative phosphorylation

Chapter 14 - Electron Transport and Oxidative Phosphorylation

  • The cheetah, whose capacity for aerobic metabolism makes it one of the fastest animals

Chapter 14


Oxidative phosphorylation in mitochondria

Oxidative Phosphorylation in Mitochondria

  • Oxidative phosphorylation is the process by which NADH and FADH2 are oxidized and ATP is formed

  • NADH and FADH2 are reduced coenzymes from the oxidation of glucose by glycolysis and the citric acid cycle

The Respiratory Electron-transport Chain (ETC) is a series of enzyme complexes embedded in the innermitochondrialmembrane, which oxidize NADH and QH2. Oxidation energy is used to transport protons across the inner mitochondrial membrane, creating a protongradient

ATP synthase is an enzyme that uses the proton gradient energy to produce ATP

Chapter 14


The mammalian cell

The Mammalian Cell

Chapter 14


Mitochondria are energy centers of a cell

Mitochondria are energy centers of a cell

Cytosol

Mitochondria

Chapter 14


Fig 14 6

Fig 14.6

Chapter 14


Fig 14 6 structure of the mitochondrion

Fig 14.6Structure of the mitochondrion

  • Final stages of aerobic oxidation of biomolecules in eukaryotes occur in the mitochondrion

  • Site of citric acid cycle and fatty acid oxidation which generate reduced coenzymes

  • Contains electron transport chain to oxidize reduced coenzymes

Chapter 14


Overview of oxidative phosphorylation

Overview of oxidative phosphorylation

Fig 14.5

Chapter 14


Electron flow in oxidative phosphorylation

Electron Flow in Oxidative Phosphorylation

  • Five oligomeric assemblies of proteins associated with oxidative phosphorylation are found in the inner mitochondrial membrane

  • Complexes I-IV contain multiple cofactors, and are involved in electron transport

  • Electrons flow through complexes I-IV

  • Complexes I, III and IV pump protons across the inner mitochondrial membrane as electrons are transferred

  • Mobile coenzymes: ubiquinone (Q) and cytochrome c serve as links between electron transport complexes

  • Complex IV reduces O2 to water

  • Complex V is ATP synthase, which uses the generated proton gradient across the membrane to make ATP

Chapter 14


Table 14 1

Table 14.1

Chapter 14


Cofactors in electron transport

Cofactors in Electron Transport

  • NADH donates electrons two at a time to complex I of the electron transport chain

  • Flavin coenzymes are then reduced

  • (Complex I) FMN FMNH2

  • (Complex II) FADFADH2

  • FMNH2 and FADH2 donate one electron at a time to ubiquinone (U or coenzyme Q)

  • All subsequent steps in electron transport proceed by one electron transfers

Chapter 14


Mobile electron carriers

Mobile electron carriers

1. Ubiquinone (Q)Q is a lipid soluble molecule that diffuses within the lipid bilayer, accepting electrons from Complex I and Complex II and passing them to Complex III.

2. Cytochrome cAssociated with the outer face of the inner mitochondrial membrane. Transports electrons from Complex III to Complex IV.

Chapter 14


Iron in metalloenzymes

Iron in metalloenzymes

  • Iron undergoes reversible oxidation and reduction:

  • Fe3++ e- (reduced substrate)

  • Fe2+ + (oxidized substrate)

  • Enzyme hemegroups and cytochromes contain iron

  • Nonhemeiron exists in iron-sulfur clusters (iron is bound by sulfide ions and S- groups from cysteines)

  • Iron-sulfur clusters can accept only one e- in a reaction

Chapter 14


Fig 7 3 iron sulfur clusters

Fig 7.3 Iron-sulfur clusters

  • Iron atoms are complexed with an equal number of sulfide ions (S2-) and with thiolate groups of Cys side chains

  • Heme consists of a tetrapyrrole Porphyrin ring system complexed with iron

Chapter 14

Fig. 4.39 Heme Fe(II)-protoporphyrin IX


Complex i nadh ubiquinone oxidoreductase

Complex I. NADH-ubiquinone oxidoreductase

  • Transfers two electrons from NADH as a hydride ion (H:-) to flavin mononucleotide (FMN), to iron-sulfur complexes, to ubiquinone (Q), making QH2

  • About 4 protons (H+) are translocated across the inner mitochondrial membrane per 2 electrons transferred

Chapter 14

Fig 14.11


Complex ii succinate ubiquinone oxidoreductase

Complex II. Succinate-ubiquinone oxidoreductase

  • Also known as succinate dehydrogenase complex

  • Transfers electrons from succinate to flavin adenine dinucleotide (FAD) as a hydride ion (H:-), to an iron-sulfur complex, to ubiquinone (Q), making QH2

  • Complex II does not pump protons

Chapter 14

Fig 14.12


Complex iii ubiquinol cytochrome c oxidoreductase

Complex III. Ubiquinol-cytochrome c oxidoreductase

  • Transfers electrons from QH2 to cytochrome c, mediatedby iron-sulfur and other cytochromes

  • Electron transfer from QH2 is accompanied by the translocation of 4 H+ across the inner mitochondrial membrane

Fig 14.13

Chapter 14


Complex iv cytochrome c oxidase

O2 + 4 e- + 4H+ 2 H2O

Complex IV. Cytochrome c oxidase

  • Uses four-electrons from the soluble electron carrier cytochrome c to reduce oxygen (O2) to water (H2O)

  • Uses Iron atoms (hemes of cytochrome a) and copper atoms

  • Pumps two protons (H+) across the inner mitochondrial membrane per pair of electrons, or four H+ for each O2 reduced

Chapter 14


Complex v atp synthase

Complex V: ATP Synthase

  • F0F1 ATP Synthase uses the proton gradient energy for the synthesis of ATP

  • Composed of a “knob-and-stalk” structure

  • F1 (knob) contains the catalyticsubunits

  • F0 (stalk) has a protonchannel which spans the membrane.

  • Passage of protons through the Fo (stalk) into the mitochondrial matrix is coupled to ATP formation

  • Estimated passage of 3 protons (H+) perATP synthesized

Chapter 14


Fig 14 17 knob and stalk structure of atp synthase

Fig 14.17 Knob-and-stalk structure of ATP synthase

Chapter 14


Mechanism of atp synthase

Mechanism of ATP Synthase

  • There are 3 active sites, one in each b subunit

  • Passage of protons through the Fo channel causes the c-e-g unit to rotate inside the a3b3 hexamer, opening and closing the b-subunits, which make ATP

Chapter 14


Fig 14 17

Fig 14.17

  • Molecular structure of of ATP synthase

Chapter 14


Fig 14 20 transport of atp adp and p i across the inner mitochondrial membrane

Fig 14.20 Transport of ATP, ADP and Pi across the inner mitochondrial membrane

  • Adenine nucleotide translocase: unidirectional exchange of ATP for ADP (antiport)

  • Symport of Pi and H+ is electroneutral

Chapter 14


The p o ratio

The P:O Ratio

molecules of ADP phosphorylated

P:O ratio = -----------------------------------------

atoms of oxygen reduced

  • Translocation of 3H+ required by ATP synthase for each ATP produced

  • 1 H+ needed for transport of Pi, ADP and ATP

  • Net:4 H+ transported for each ATP synthesized

Chapter 14


Calculation of the p o ratio

Calculation of the P:O ratio

ComplexIIIIIV

#H+ translocated/2e- 4 4 2

Since 4 H+ are required for each ATP synthesized:

For NADH: 10 H+ translocated / O (2e-)

P/O = (10 H+/ 4 H+) = 2.5 ATP/O

For succinate (FADH2) substrate = 6 H+/ O (2e-)

P/O = (6 H+/ 4 H+) = 1.5 ATP/O

Chapter 14


Regulation of oxidative phosphorylation

Regulation of Oxidative Phosphorylation

  • Overall rate of oxidative phosphorylation depends upon substrateavailability and cellularenergydemand

  • Important substrates: NADH, O2, ADP

  • In eukaryotes intramitochondrial ratio ATP/ADP is a secondary control mechanism

  • High ratio inhibits oxidative phosphorylation as ATP binds to a subunit of Complex IV

Chapter 14


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