chapter 18 oxidative phosphorylation the process in which atp is formed as a result of the transfer...
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Chapter 18 Oxidative phosphorylation the process in which ATP is formed as a result of the transfer of
electrons from NADH or FADH2 to O2 by a series of electron carriers
take place in mitochondria, the major source of ATP in aerobic
organisms
the culmination of a series of energy transformations that are called cellular respiration or simple respiration (p. 503)
Electron-motive force
NADH-Q oxidoreductase, Q-cytochrome c oxidoreductase,
cytochrome c oxidase
Proton-motive force
Phosphoryl transfer potential (ATP synthase)
Proton gradients are an interconvertible currency of free energy in biological systems
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(oxidative phosphorylation)
(TCA cycle,
fatty acid oxidation)
§18.1 Oxidative phosphorylation in eukaryotes takes place in
mitochondria: 2 m in length and 0.5 m in diameter
Kennedy and Lehninger
quite permeablevoltage-dependent anion channel (mitochondrial porin)
Impermeablea large family of transporters shuttles metabolites matrix side (N side) cytosolic side (P side)
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1M reduction potential of H+:H2 couple = 0
§18.2 Oxidative phosphorylation depends on electron transfer
Measurement of redox potential (E0’)
to evaluate electron-transfer potential (G°’)
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½ O2 + NADH + H+ H2O + NAD+
G0' = - 52.6 kcal mole-1 p. 508
Release energy is used
1. proton gradient formation ATP synthesis
ATP hydrolysis G0' = -7.3 kcal mole-1
2. transport metabolites across the Mito. membrane H+
matrix cyto: 5.2 kcal mole-1
G°= -nF E0 faraday (23.05 kcal mol-1V-1)
△ G = RT ln(C2/C1) + ZF V△pH lower
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§ 18.3 Four complexes in respiratory chain
Electron affinity high
Respirasome
1,2,3
1,2,4 ?
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Nelson
does not pump protons
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N P
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Respiratory chain complexes separation
ATP synthase (complex V)
In vitro, hydrolytic activity
Nelson
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Universal electron acceptors:
NADH and NADPH:
are water soluble, can’t cross inner Mito. membrane
carry e- from catabolic rxs. vs. supply e- to anabolic rxs.
[reduced form]/[oxidized form]
hydride
Nelson
UV
p. 499
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Universal electron acceptors:
Flavin nucleotides (FMN or FAD):
are bound to flavoproteins which determine the reduction potential of a
flavin nucleotide
a part of the flavoprotein’s active site
flavoproteins can participate in either one- or two- electron transfer
Nelson
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Universal electron acceptors:
Ubiquinone (coenzyme Q, Q):
a lipid-soluble molecule
can accept one or two e-
carry both e- and proton
Nelson
Q pool:
a pool of Q and QH2
exist in the inner Mito.
membrane
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Universal electron acceptors:
iron-sulfur proteins: one-electron transfer
non-heme iron proteins
without releasing or binding protons
1 Fe — 4 Cys 2 Fe — 2 S — 4 Cys 4 Fe — 4 S — 4 Cys
Rieske iron-sulfur proteins:
2 His residues replace 2 cys residues
Nelson
p. 511
Phosphorylation at His
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Universal electron acceptors:
cytochromes: a, b, c three classes in Mito.
one-electron transfer
The longest-wavelength 600 nm
560 nm
550 nm
Covalently associated to proteins
The standard reduction potential (p. 507)
Nelson
(C17)
Vinyl group
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Reduced state (Fe2+) Nelson
Color?
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1. NADH-Q oxidoreductase (NADH dehydrogenase, complex )Ⅰ
NADH + Q + 5H+matrix NAD+ + QH2 + 4H+
cytosol
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Nelson2. Succinate-Q reductase (complex Ⅱ)
p. 528
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Q cycle:
semiquinone radical anion
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Nelson
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3. Q-cytochrome c oxidoreductase (cytochrome bc1 complex; cytochrome reductase; complex )Ⅲ
His replace cys
1e-
1e-
Q 3(hemes)cytochrome c 1(2Fe-2S) during Q cycle
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4 cyt cred + 8 H+N + O2
4 cyt cox + 2 H2O + 4 H+P
4. Complex : Cytochrome c oxidase Ⅳ
e- from cytosol to O2
2 heme a, 3 copper ions
3 subunits
CuA/CuA heme a
heme a3 CuB O2
ferric/ferrous cupric/cuprous
?Nelson
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1st e-
Cupric (Cu2+)
Cuprous (Cu+)
2nd e-
Ferric (Fe3+)
Ferrous (Fe2+) 3th and 4th e-
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Proton transport by complex Ⅳ4 cyt cred + 8 H+
N + O2 4 cyt cox + 2 H2O + 4 H+P
Charge neutrality and
Conformational changes
(p. 517)
G0’
4 H+ 5.2 kcal/mole (p. 509)
2 23.06 0.82
(Tab. 18.1)
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only electrons transfer,
no protons transport
NADH + 11 H+N + ½ O2 → NAD+ + 10 H+
p + H2O
FADH2 6
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Reactive (active) oxygen species (R[A]OSs)
superoxide radical (·O2-), peroxide (O2
2-), hydrogen peroxide (H2O2), hydroxyl radical (OH·), singlet oxygen (O2
1)
superoxide dismutase (SOD): Cu/Zn-; Mn-; Fe-
catalase (CAT): 2 H2O2 O2 + 2H2O a heme protein
peroxidase: H2O2 + RH2 2 H2O + R [ascorbate or glutathione peroxidase]
SOD: 2 ·O2- + 2H+ O2 + H2O2
Dismutation: a reaction in which a single reactant
is converted into two different products
Antioxidant vitamins:
Vit C:
Vit E: lipophilic, avoid lipid peroxidation
Danger lurks in the reduction of O2
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Radical ·Q– from complex Ⅰ to QH2
QH2 to bL of complex III
Also from pentose phosphate pathway
Nelson
p. 722
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Type : insulin dep.Ⅰ
a paucity of pancreatic cells
Type : non-insulin dep.Ⅱ
slow to develop,
in older, obese individuals
insulin is produced, but some feature of
the insulin-response system is defective
The characteristic symptoms of both types:
polydipsia, polyuria, glucosuria
Aerobic metabolism
More ROS
More protective enzymes were induced