EXAM 3: OXPHO Flashcards
carbs, lipids, amino acids are the main…
reduced fuels for the cell
in oxidative phosphorylation,
energy from NADH and FADH2 are used to make ATP
if a prokaryote lives in an oxygenate environment,
oxidative phosphorylation can be done using the plasma membrane
energy of oxidation is used to
phosphorylate ADP
chemiosmotic theory
series of energy translations that results in energy for phosphorylation of ADP
energy released by electron transport…
is used to transport protons against the electrochemical gradient
favorable redox reactions are used to make this gradient
energy needed to phosphorylate ADP is provided by the
flow of protons down the electrochemical gradient
not result of a direct reaction
bacteria
plasma membrane
mitochondria
inner membrane
chloroplasts
thylakoid membrane
four distinct compartments of double membrane
outer
IMS
inner membrane
matrix
Outer membrane
relatively porous membrane, allows passage of metabolites
IMS
similar to cytosol; higher proton concentration, lower pH
inner membrane
relatively impermeable, proton gradient across it
location of electron transport chain complexes (including succinate dehydrogenase as part of Complex II)
infolding of membrane produces cristae - serves to increase surface area
matrix
location of CAC and parts of lipid and amino acid metabolism
lower proton concentration, higher pH
electron transport chain complexes
each complex (4) have multiple redox centers with:
FMN/FAD
cytochromes a,b,or c
iron-sulfur clusters and heme groups
Cu centers and FeCu centers
FMN / FAD
FMN: complex 1
FAD: complex 2
initial electron acceptors
can carry two electrons but transfer one at a time
iron-sulfur centers
one electron carriers
coordinated by stationary cysteines in the protein
contain variable numbers of iron and sulfur atoms; multiple ions, multiple transfers
cytochromes
proteins or subunits of complexes containing heme prosthetic groups
one electron carriers
iron coordinating porphoryin ring derivatives ring determines cytochrome type)
can be mobile or stationary
coenzyme Q
ubiquinone
ubiquinone
lipid-soluble conjugated dicarbonyl compound that readily accepts electrons
transfer 1 or 2 electrons at a time
upon accepting 2 electrons, picks up two H+ —> ubiquinol
ubiquinol
can freely diffuse in the membrane, carrying electrons with protons
mobile electron carrier transporting electrons from Complex 1 or 2 to 3
ubiquinone
Q
oxidized, hydrophobic tail in membrane
ubiquinol
QH2
fully reduced
free energy of electron transport
electrons are spontaneously transferred from molecules with lower reduction potentials to molecules with higher reduction potentials
the free energy released is used to pump protons, storing this energy as the electrochemical gradient
COMPLEX 1
NADH: ubiquinone oxidoreductase
large; over 40 diff pp chains encoded by nuclear and mitochondrial DNA
COMPLEX 1 process
NADH binding site on matrix side of membrane
FMN noncovalently bound, accepts 2 electrons from NADH
passes one at a time to iron-sulfur clusters
several iron sulfur clusters pass one electron at a time to ubiquinone binding site within the membrane
ubiquinone is reduced to ubiquinol
2 electrons from NADH to Q is accompanied by a transfer of 4 protons from the matrix (N) to intermembrane space (P) via transporters
reduced Q picks up 2 H+
COMPLEX II:
SUCCINATE DEHYDROGENASE
succinate oxidized to fumarate
FAD accepts 2 electrons from succinate to make FADH2
electrons passed one at a time via iron sulfur centers to Q which picks up 2 H+ to become QH2
net protons pumped at complex 1
4; 2 picked up for QH2
net protons pumped at complex 2
0
2 dropped off by FADH2
2 picked up by Q
why do you only get 2.5 ATP from NADH and only 1.5 ATP from FADH2?
NADH at complex 1 pumps 4 protons to the IMS while at complex 2 there are 0 protons pumped/ the gradient is not affected
COMPLEX III:
UBIQUINONE; CYTOCHROME C OXIDOREDUCTASE
2 electrons from QH2 to reduce 2 molecules of cytochrome C
iron sulfur clusters, cytochrome b, cytochrome c
Q CYCLE: 4 additional protons added to IMS
THE Q CYCLE
4 protons are added to the IMS per two electrons that reach cytochrome c
\_\_\_\_\_\_\_\_ 2 molecules of QH2 become oxidized 2 cytochrome c reduced 2 protons from each QH2 goes to IMS 1 Q gets reduced using 2 electrons from QH2 oxidation 2 protons from the matrix reduce Q
Q CYCLE PROCESS
Q, QH2, C bind
QH2 oxidizes, e goes to Q, e goes to C, 2H+ goes to IMS
C is reduced, leaves to complex 4; oxidized Q leaves; Q* stays
new QH2 binds, new C binds
QH2 oxidizes, e goes to Q*, e goes to C, 2H+ go to IMS
2H+ go to Q*+e
C is reduced, goes to complex 4; oxidized Q leaves; reduced QH2 leaves
q cycle overall
QH2 + 2cytC (ox) + 2H+n
2 cyto c reduced 4 protons to IMS 2 protons out of matrix oxidized 2 Q reduced 1 QH2
net equation:
Q + 2 cytC (red) + 4H+p
cytochrome c
second mobile electron carrier
soluble heme containing protein in the IMS
heme iron can be oxidized (3+) or reduced (2+)
carries single electron from Complex III to Complex IV
COMPLEX IV:
CYTOCHROME OXIDASE
13 subunit membrane protein
2 heme groups; a, a3
copper ions at 2 sites; CuA, CuB
CuA
two ions that accept electrons from cyto c
CuB
bonded to heme a3; forming binuclear center that transfers 4 electrons to oxygen
passing of electrons to O2 in complex 4
4 cytochrome C reduced from complex 3 bring electrons to complex 4 and are oxidized
4 electrons used to reduce 1 oxygen to make 2 water molecules
4 H+ picked up from the matrix; helps build gradient
4 H+ additional are pumped from matrix to IMS
reduction of O2 provides enough energy to remove 4H+ from matrix AND pump 4 H+ to IMS
reducing oxygen equation
½ O2 —> H2O
2 cyto C
2 e-
2 H+ substrate
2 H+ pumped
Complex 1 to complex 4
NADH + 11 H+n + ½ O2
NAD+ + 10H+p + H2O
2.5 ATP
dG = -220kJ/mol
Complex 2 to complex 4
FADH2 + 6H+n + ½ O2
FAD+ + 6H+p + H2O
1.5 ATP
dG = -150 kJ/mol
(less energy from transport, less protons to IMS, less ATP made)
proton motive force
proteins in the ETC created the electrochemical proton gradient by 1 of 3 means
- actively transporting protons across the membrane (Complex 1, Complex IV)
- chemically removing protons from the matrix (Complex 3 reduction of Q, reduction of oxygen Complex IV)
- release of protons into the IMS (Oxidation of 2 QH2 in Complex III)
chemiosmotic model for ATP synthesis
electron transport sets up a proton-motive force
energy of proton-motive force drives synthesis of ATP via controlled release
CN-
blocks electron transfer to oxygen;
ATP synthesis is shut down because electron transport is shut down, there is no energy from electron transport driving the proton gradient
oligomycin
inhibits ATP synthesis; shuts down electron transport as well because ATP synthesis dissipates the proton gradient
DNP
uncouples reactions; equalizes H+ concentrations across the membrane by allowing the gradient to dissipate
O2 is still consumed and protons are pumped to the IMS but ATP synthesis does not occur
mitochondrial ATP synthase complex
2 functional units: F1, F0
F1
soluble complex in the matrix
catalyzes synthesis from ADP and Pi
F0
integral membrane complex
transports H+ from IMS to matrix, dissipating gradient
energy transfers to F1 to catalyze phosphorylation of ADP
F1 hexamer
arranged in 3 alpha-beta dimers
dimers have 3 conformations
beta empty: nothing bound
beta ADP: ADP and Pi bound loosely
beta ATP: catalyzes ATP formation by binding product tightly
synthase
no ATP
synthetase
ATP
coupling proton translocation to ATP synthesis
proton translocation causes a rotation of the F0 and the central shaft gamma subunit
rotation of the shaft causes a conformational change within all three alpha-beta pairs
the conformational change in one of the 3 pairs promotes the condensation of ADP and Pi into ATP
the biggest conformational change allows ATP to leave because it was previously tightly bound
adenine nucleotide translocase
antiporter; ATP4- in IMS, ADP3- in matrix
phosphate translocase
symporter
phosphate, H+ into matrix
2 ways to get NADH from cytosol into mitochondria
glycolysis to ETC
malate aspartate shuttle
glycerol 3P shuttle
malate aspartate shuttle
electrons given to malate via malate dehydrogenase which has transporter into matrix where NADH is regenerated
aspartate is transported out to cytosol to continue shuttle
NADH goes through complex I to get 2.5 ATP for each NADH
malate + NAD+ —> oxaloacetate —> aspartate —> oxaloacetate + NADH…
malate dehydrogenase; aspartate aminotransferase
glycerol 3P shuttle
electrons given to dihydroxyacetone phosphate (ox) to make glycerol 3P (red) —> glycerol 3P dehydrogenase (cytosolic)
oxidation of glycerol-3P back to DHAP reduces FAD to FADH2 —> glycerol 3P dehydrogenase (mitochondrial)
electrons transferred from FADH2 to Q —> QH2 which goes to complex 3 to get 1.5 ATP for each FADH2
regulation of OXPH
substrate availability:
NADH or FADH2 and ADP/Pi
due to coupling: substrates required for both ETC and ATP synthesis
inhibition leads to accumulation of NADH —> inhibits enzymes in glycolysis, CAC
inhibitor of F1
IF1
ATP synthase can work in reverse when there is no proton gradient
IF1 works in matrix; prevents hydrolysis of ATP during low oxygen by preventing ATPase from turning backwards
active at lower pH when electron transport is stalled due to low O2 and H+ remains in matrix
