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Explain the benefits of having the electron-transport chain located in a membrane. ✓ Described how the proton-motive force is converted into ATP.
Typology: Summaries
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-^ Chapter
-^ Chapter
-^ Oxidative
phosphorylation
captures
the^ energy
of^ high
‐energy
electrons
to^ synthesize
-^ The flow^ of
electrons
from^ NADH
and^ FADH
to^ O 2 2 occurs
in^ the
electron
‐transport
chain^
or^ respiratory
chain.
-^ This
exergonic
set^ of^
oxidation
‐reduction
reactions
generates
a^ proton
gradient. • The^ proton
gradient
is^ used
to^ power
the^ synthesis
of^ ATP.
-^ Collectively,
the^ citric
acid^ cycle
and^ oxidative
phosphorylation
are
called^
cellular
respiration
or^ simply
respiration
cellular
respiration
Electron micrograph (A)and diagram (B) of a mitochondrion
-^ The
outer^
mitochondrial
membrane
is^ permeable
to^ most
small^ ions
and
molecules
because
of^ the
channel
protein
mitochondrial
porin.
-^ The
inner^ membrane,
which
is
folded^
into^ ridges
called cristae,
is
impermeable
to^ most
molecules.
-^ The
inner^ membrane
is^ the^
site^ of
electron
transport
and^ ATP synthesis. • The^ citric
acid^ cycle
and^ fatty
acid
oxidation
occur^
in^ the^ matrix.
Biological
Insight:
Sequence
data^ suggest
that
all^ mitochondria
are^ descendants
of^ an
ancestor
of^ Rickettsia
prowazekii
,^ which^ was
engulfed
by^ another
cell.^
The^ reduction
potential
E ′,^ or^0 redox^
potential,
is^ a^ measure
of^ a^ molecule’s
tendency
to^ donate
or^ accept
electrons.
A^ strong
reducing
agent^
readily
donates
electrons
and^ has
a^ negative
A^ strong
oxidizing
agent^
readily
accepts
electrons
and^ has
a^ positive
The^ standard
free‐energy
change
is^ related
to^ the
change
in^ reduction
potential. where^
n^ is^ the
number
of^ electrons
transferred
and^ F^
is^ the^ Faraday
constant.
Energy
is^ released
when^
high‐energy
electrons
are^ transferred
to^ oxygen.
The^ energy
is^ used
to^ establish
a^ proton
gradient.
-^ The
electron
‐transport
chain^
is^ composed
of^ four
large^ protein
complexes. • The^ electrons
donated
by^ NADH
and^ FADH
are^ passed 2
to^ electron
carriers
in^ the protein
complexes.
-^ The
carriers
include
flavin mononucleotide
iron^ associated
with
sulfur^ in
proteins
(iron‐sulfur
proteins),
iron^ incorporated
into^ hemes that
are^ embedded
in^ proteins
called cytochromes,
and^ a^
mobile
electron
carrier
called
coenzyme
-^ Electron
flow^ within
the^ complexes
in^ the^
inner‐mitochondrial
membrane
generate
a^ proton
gradient.
-^ These
complexes
appear
to^ be^ associated
with^ one
another
in^ what
is
called^ the^ respirasome.
Iron–sulfur clusters
(A)^ A single iron ion bound by four cysteine residues.
(B)^ 2Fe-2S cluster with iron ions bridged
by sulfide ions.
(C)^ 4Fe-4S cluster. Each of these clusters can undergo oxidation–reduction reactions. •^ Frataxin
is^ a^ mitochondrial
protein
required
for^ the
synthesis
of^ iron
‐sulfur
clusters. • Loss^ of
frataxin
results
in^ Friedreich’s
ataxia,
a^ disease
that^ affects
the^ nervous
system
as^ well
as^ the
heart^
and^ skeletal
system.
-^ Coenzyme
Q^ is^ derived
from^ isoprene.
-^ Coenzyme
Q^ binds
protons
as^ well
as
electrons,
and^ can
exist^ in
several
oxidation
states. • Oxidized
and^ reduced
Q^ are^
present
in^ the
inner^ mitochondrial
membrane
in^ what
is
called^
the^ Q^ pool.
-^ The
electrons
from^ NADH
are^ passed
along^
to^ Q^ to
form^ QH
by^ Complex 2
leaves^
the^ enzyme
for^ the
Q^ pool
in^ the^
hydrophobic
interior
of^ the
inner‐
mitochondrial
membrane.
-^ Four
protons
are^ simultaneously
pumped
out^ of
the^ mitochondria
by^ Complex
Electrons
from^ QH
are^ used 2
to^ reduce
two^ molecules
of^ cytochrome
c^ in
a^ reaction
catalyzed
by^ the
Q‐cytochrome
c^ oxidoreductase or
Complex
III.^ Complex
III^ is^ also
a^ proton
pump.
carries 2
two^ electrons
while^
cytochrome
c^ carries
only^ one
electron.
-^ The
mechanism
for^ coupling
electron
transfer
from^ QH
to^ cytochrome 2
c^ is
called^ the^ Q^ cycle.
-^ In^ one
cycle,^
four^ protons
are^ pumped
out^ of
the^ mitochondria
and^ two
more
are^ removed
from^ the
matrix.
carries 2
two^ electrons
while^
cytochrome
c^ carries
only^ one
electron.
-^ The
mechanism
for^ coupling
electron
transfer
from^ QH
to^ cytochrome 2
c^ is
called^ the^ Q^ cycle
Definition: •^ The
Q^ cycle
is^ a set
of^ reactions
in^ which
coenzyme
Q^ cycles
between
the
fully^ reduced
state^ and
the^ fully
oxidized
state^ through
one‐electron
transfer
reactions
in^ which
one^ of
the^ electrons
is^ temporarily
stored
in;
provides
a^ means
of^ passing
the^ two
electrons
of^ coenzyme
Q^ to^ the
single‐
electron
carrier
cytochrome
c ,^ one
electron
at^ a^ time.
-^ In^ one
cycle,^
four^ protons
are^ pumped
out^ of
the^ mitochondria
and^ two
more^ are
removed
from^ the
matrix.
