lecture 6+7 Flashcards
mitochondrial proton gradient
proton-motive force- potential energy for ATP synthesis
electric transport chain & ATP synthesis
chemical potential ∆ph (inside alkaline)
->ATP synthesis driven by proton-motive force
-> electric potential ∆psi (inside negative)
electron transport and oxidation phosphorylation
capture the energy in the redox potential of NADH and FADH2
coupling depends on
-sequential redox reactions that pass electrons from NADH to O2
-the compartmentalization of these reactions in the mitochondrion
-the generation of a proton gradient from the above
energy from glucose
is used to produce ATP
2 ways ATP is produced
-substrate level phosphorylation
-oxidative phosphorylation
electron transport
electrons carried by reduced coenzymes are passed through a chain of proteins and coenzymes
-drives the generation of a proton gradient across the inner mitochondrial membrane
oxidative phosphorylation
the proton gradient runs downhill to drive the synthesis of ATP
electrons pass
from electron donors to acceptors
each subsequent electron acceptor
“wants” the electron more than the previous acceptor
E°’ = standard reduction potential
A measure of how easily a compound can be reduced
the more positive the standard reduction potential
the more the compound “wants” electrons
in the ETC
carrier function is in the order of increasing reduction potential
electrons move spontaneously
from carriers of low E°’ to carriers of higher E°’
electrons flow through
a series of membrane-bound carriers
four groups: complexes
includes integral and peripheral membrane proteins
use metal containing prosthetic groups or flavins to carry electrons
Ubiquinone
a lipid-soluble carrier molecule
Coenzyme Q/benzoquinone
lives in mitochondria membrane
isoprenoid side chain
hydrophobic anchor
for coenzyme Q to complete reduction it requires
2 electrons and 2 protons
(gets them from matrix)
Q shuttles electrons from
complex I and II to complex III
electron carrying groups
heme prosthetic groups(cytochromes), iron-sulfur groups(complexes I-III)
protein complex
includes FMN and Fe-S centers
electrons flow:
NADH - FMN
FMNH2-Fe3+
Fe3+-Fe2+
electrons ultimately
shuttled to Q
energy of electron transfer
used to pump 4 H+
complex 1
NADH -dehydrogenase
complex 2
succinate dehydrogenase
succinate + FAD
fumerate + FADH2
Complex III:
Ubiquinone:Cytochrome C reductase
electron flow
ubiquinone to cytochrome C
oxidation of one QH2
moves 4+ across the inner mitochondrial membrane
complex 4
uses the energy of reduction of O2 to pump one H+ into the intermembrane space for each electron that passed through
4 Cyt C(red) +8 H+n +O2
4 Cyt C(oxi) +4 H+p + 2 H2O
it takes 2 NADH and uses 4 H+
to reduce one O2
for one pair of electrons
creates electrochemical gradient for protons to flow down and drive ATP synthesis
NADH 10 H- pumped
3 ATP
FADH2 6 H+ pumped
2 ATP
ETC inhibitors
rotenone,antimycin A ,cyanide
ATP synthase
protons move passively back into the matric through this. special transmembrane protein using electrochemical gradient
Complex V (atp synthase)
a multisubunit transmembrane protein
two functional units of atp synthase
F1 and F0
F1
water-soluble peripheral membrane protein complex
generates 1 ATP
for every 3 protons through the complex
F0: transmembrane proton core
3 subunits:ab2c10-12
b subunit
stabilizes F1
C subunit
made up of small hydrophobic a-helices arranged in concentric circles
what causes the rotation of the c subunit
protons flow through c pores
F1 synthase structure
alternating alpa and beta subunits around a central gamma subunit
one domain of gamma forms central shaft
second domain associates with beta subunits
Three interacting catalytic beta subunits
each with a different conformational state
beta-adp
not catalitically active, binds adp and p
beta -atp
catalytically active, binds atp
beta empty
low affinity for adp or atp
free energy generated with proton movement is harnessed
to interconvert the conformation states to make and release ATP
conformational changes are
driven by the rotation of the rotor(c and gamma subunits)
relative to the alpha beta subunits
3H+
for every 120 turn
conversion of beta-ADP to beta-ATP
synthesis of atp
conversion of beta -ATP to beta-ADP
release of ATP
when one beta subunit assumes beta empty
one neighbor assumes beta-adp
one neighbor assumes beta atp
one complete rotation of gamma
causes each of beta to assume all 3 conformations
3 ATP FOR 360°
actin filament “jumps” in 3 steps of 120 moves in one direction
supports 3-stage binding change model
cellular respiration: the payoff
yield: an average of 3 atp per nadh; 2 ATP per FADH2
anaerobic fermentation
only 2 ATP/glucose
isolated mitochondria
O2 electrodes
buffer assayed for ATP
need both a source of electrons(succinate) and ADP+P
to get respiration and atp synthesis
what blocks atp synthesis
venturicidin & oligomycin H+ build up but soon energy to pump H+ against gradient exceeds energy of ETC
uncouplers such as DNP can carry protons from P to N side
this dissipates the H+ gradient so etc begins again
thus can etc without ATP synthesis
electron transport can be uncoupled from atp synthesis
2,4-dinitrophenol
very hydrophobic, dissociable proton
can carry H+ across inner mitochondrial membrane
(destroys H+ gradient)
occurs in brown fat:
many mitochondria and cytochromes
oxidation of NADH uncoupled from ATP synthesis
energy of ETC is released as heat (found in newborn mammals)
pore protein called thermogenin
allows protons to flow down gradient and release as heat
