20. the ETC Flashcards
define oxidative phosphorylation
the culmination of energy-yielding metabolism in aerobic organisms
what type of electron carriers were produced by glycolysis, pyruvate oxidation, and CAC
reduced electron carriers (NADH and FADH2)
what happens to the electrons of the reduced electron carriers during the ETC
the electrons are passed to proteins, and oxygen is the ultimate electron acceptor, and the energy of oxidation is used to make ATP
where is the ETC
in the inner mitochondrial membrane
for the ETC, where in the cell do the reduced electron carriers arrive
in the mitochondrial matrix side of the IMM
in the ETC where in the cell is the H+ gradient generated
in the intermembrane space of the mitochondria
for the ETC where in the cell does the ATP go as it’s made from ATP synthase
mitochondrial matrix
what two processes make up oxidative phosphorylation
the ETC and chemiosmosis
what happens once O2 accepts the electrons at the end of the ETC
water is made
T or F: electron movement through the ETC is spontaneous
true
why is electron movement through the ETC spontaneous
each subsequent carrier has a higher reduction potential (ie each carrier wants the electrons more) until we reach oxygen
how is the energy extracted from the oxidation reactions of the ETC conserved
the energy is used to establish a proton gradient across the IMM
what is the purpose of establishing a proton gradient across the IMM
the electrochemical potential will drive ATP synthesis, and the conversion to ATP is unfavorable which is why it requires the energy input from the gradient
T or F: ATP production in the ETC is considered to be substrate level phosphorylation
false; because the ATP production is not a result of a direct reaction between ADP and some high-energy phosphate carrier
describe the outer membrane of the mitochondria
relatively porous, allows passage of metabolites but not proteins through large transmembrane porin complexes
describe the IMM of the mitochondria
similar environment to the cytosol, high H+ concentration than the matrix
describe the inner membrane of the mitochondria
impermeable to almost all metabolites (they need specific transporters to pass), have cristae which increase SA, location of ETC and ATP synthase
describe the matrix of the mitochondria
lower H+ concentration than the IMM, location of the CAC and PDH complex
define redox pair
an electron donor and an acceptor in a redox reaction
what is ∆Eo′
standard reduction potential
what are the units for ∆Eo′
volts (V)
what is the formula for finding ∆Eo′ from the redox reaction
∆Eo′ = Eo′(electron acceptor) -Eo′(electron donor)
what does a high ∆Eo′ value mean
greater electron affintiy
how is ∆Eo′ related to ∆Go′
∆Go′ = –nF∆Eo′
what is F in the reaction ∆Go′ = –nF∆Eo′
Faraday’s constant (96,480 J/V x mol)
what is the ∆Eo′ for the entire ETC
1.14 V
what are the three key mechanisms of electron transfer through the respiratory chain
direct transfer (ie Fe3+ to Fe2+), transfer as an H (H+ and e-), and transfer as a hydride ion (:H- has 2 e-)
define reducing equivalent
used to designate a single electron equivalent transferred in a redox reaction
other than NADH and FADH2, which carriers are used in the ETC
ubiquinone, cytochromes, and iron-sulfur proteins
how many electrons can quinone carry
1 or 2
how many electrons can quinone pick up
1 for each electron
T or F: ubiquinone is mobile
true
list the other two names of ubiquinone
coenzyme Q, or Q
what is ubiquinone called when reduced
QH2
what are cytochromes
proteins with iron containing heme prosthetic groups
how many electrons can cytochromes carry
1
how many types of cytochromes does the mitochondria have
3: a, b, and c
T or F; cytochromes absorb visible light
true
why do cytochromes absorb visible light
due to the ringed delocalized electrons
describe the structure of each cytochrome
a has a long isoprenoid tail, and both a and b are tightly bound to large protein complexes, but c is not
what characteristic does cytochrome c have since it isn’t attached to a large protein complex like a and b are
it associates with the outer surface of the IMM through electrostatic interactions, allowing it shuttle electrons between two less mobile complexes
describe the structure of iron-sulfur proteins
iron atom is associated with a sulfur atom (from Cys, inorganic sulfur, or both). Together they make an Fe-S center of varying complexity
how many electrons can Fe-S proteins carry
1
how many Fe-S proteins are involved in the ETC
at least 8
how are the electron carriers of the ETC organized
organized into membrane-embedded supramolecular complexes
how many supramolecular complexes are there in the ETC
4
what are the two pathways of the supramolecular complexes of the ETC
1 to 3 to 4
2 to 3 to 4
T or F: electrons move from complex 1, through 2 and 3, and then to 4
false; electrons will never go through all 4. They either go 1,3,4 or 2,3,4
complex I: what carriers do electrons move between
NADH to Q
complex I: describe the structure
45 dif polypeptide chains and 8 Fe-S centers
complex I: where is the NADH binding site
the matrix side
complex I: what happens to the electrons when NADH binds to its binding site
noncovalently found flavin monocucleotide (FMN) accepts the 2 electrons. Fe-S centers pass electrons one at a time towards the Q binding site
complex I: describe the exergonic and endergonic transfers that occur as electrons move
exergonic: hydride ion and a proton from the matrix go to Q
endergonic: transfer of 4 protons from the matrix to the IMM against their gradient
complex I: how many protons are pumped into the IMM
4
complex II: which carriers move the electrons
succinate to Q
complex II: describe the structure of succinate dehydrogenase
4 subunits: 2 membrane bound and 2 extending into the matrix
complex II: describe the electron movement
succinate donates electrons to FAD to produce FADH2, then they move through a series of Fe-S centers until they reach the Q binding site where we get QH2
complex II: how many protons are moved into the IMM
ZERO
complex III: what carriers do electrons move between
ubiquinol to cytochrome C
complex III: describe the two key transfers that occur
exergonic of two electrons from ubiquinol (QH2) to two molecules of soluble cytochrome c
endergonic of 4 protons into the IMM against their gradient
complex III: how many protons are pumped into the IMM
4
complex III: how many electrons can cytochrome c hold at a time
only 1
complex III: what is the result of cytochrome c only being able to hold 1 of the 2 electrons at a time
QH2 will go back and forth as it shuttles electrons and protons across (the Q cycle)
the Q cycle: describe the first half of the process
one QH2 on the IMS side releases two protons into the IMS. One of the lost electrons moves towards the matrix and the other goes to cytochrome c. This leaves us with Q, and a partially reduced cytochrome c
the Q cycle: describe the second half of the process
a Q on the matrix side accepts the lone electron (Q-) and a second molecule of QH2 repeats the process (2 H+ donated to IMS, one electron to Q- = QH2 and one to cytochrome c = fully reduced cytochrome c)
the Q cycle: describe the net effects
one QH2 becomes fully oxidized (two were, but we produced one QH2 too), two cyt c molecules are reduced (one electron received by each), 4 H+ into the IMS, two protons from the matrix are consumed
complex IV: what carriers are involved
cytochrome c to O2
complex IV: what is the role of copper
copper is complexed with two SH groups from Cys to form a binuclear center called CuA
complex IV: what is the role of heme
CuA will donate the electron from cytochrome c through some heme groups, and the hemes will pass the electron to O2
complex IV: how many protons are pumped into the IMM for every electron pair
2
from the 2 electrons donated from NADH, what is made?
10 H+ into the IMS, 1 H2O made
from the 2 electrons from FADH2, what is produced?
6 H+ into the IMS, 1 H2O made
what is the affect of the difference in the number of the H+ pumped into the IMS from NADH and FADH2
the difference in the H+ pumped into the IMS impacts the amount of ATP made
(NADH –> 2.5 ATP)
(FADH2 –> 1.5 ATP)
which electron carrier is better at making ATP; NADH or FADH2
NADH
describe the two components of the proton motive force
- the chemical potential energy due to the dif in conc. of H+ across a membrane
- the electrical potential energy die to the separation of charge when an H+ moves across a membrane without a counterion
describe regulation of the ETC
- ATP is only formed as fast as it can be used
- glycolysis, pyruvate oxidation, CAC, ETC, and chemiosmosis are all accelerated or inhibited together
