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BCH210H1 Study Guide - Reduction Potential, Field Museum Of Natural History, Citric Acid Cycle

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Michael Baker

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BCH210H © Lisa Zhao 2012 | Page 1
Lecture 30: Electron Transport
use of energized electrons from the reduction rxns and the reduced coenzymes NADH, FADH2 QH2
to produce ATP
krebs cycle, PDH complex in matrix
SDH is attached to inner membrane
ETC takes place in the inner membrane and matrix
inner membrane is the location for e- flow coming from the donors
electrons come down a series of carriers found in the inner membrane
e- start at FADH2 and NADH
NADH can only accommodate 1e- in its reduced structure, so the 2 e- are balanced by 1 H+
o NADH + H+
FADH2 has the 2 protons built in
transit of e- down carriers down an NRG hill (NRG slope)from donors to acceptors (each
carrier can exist as a reduced or oxidized form, as an reducing agent or oxidizing agent)steps
(gradual release) instead of sudden release of e- conserves NRG and produce ATP
where NRG is defined by reduction potential
o the NRG of reduction associated w these e- is establishing the nature of this NRG hill
as NRG is going down NRG hill, the NRG is released
series of redox rxs
last receptor is O2
it will pick up e- and form H2O
o H2O doesn’t give up its e- easily, and thus is the last product
e- from NADH to H2O
outer membrane has pores
inner membrane is tight (location of e- transport carriers)
as reduction potential of e- decreases as e- are passing through carriers, NRG is released and ATP is
standard reduction potential (E0)the ability of a reducing agent to lose e-
under standard conditions
NADH: E0 = -0.32 volts
good e- donor
gives up e- easily
good reducing agent
H2O: E0 = +0.82 volts
poor reducing agent
doesn’t give e- up
goes from a good reducing agent through a series of gradually lower reducing potentials
e- flow from more negative to more positive E0
e- carriers are arranged in complexes in the inner membrane (focal areas of e- transport)
related ones that transport to each other are located in groups (complexes)
e- transport from complex to complex
Complex 1
NADH entering
very NRGetic e-
NADH-DH creates an e- flow
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BCH210H © Lisa Zhao 2012 | Page 2
e- enter and proceed through carriers
NADH donates its e- and 2 protons for reduction of next carrier FMN
FMN has higher ΔG° than FAD but has similar structure, more NRGetic
FMN is reduced by e- and 2 protons are added resulting in FMNH2
NADH is the reducing agent
loses its e-
FMN picks up e- which becomes than reduced
FMNH2 uses its e- to reduce CoenzymeQ
FMNH2 transfers e- and 2 protons to reduce CoQ to produce CoQH2
NRG drop from -0.32 V to +0.04 V allows production of ATP
Complex 2
SDH is also a member of the Krebs Cycle(is the one attached to the inner membrane)
has a FADH2
(for SDH to work, need to convert FADH2 quickly to FAD)
FAD and FADH2 are tightly attached to SDH
need to take e- and protons away to get cycle
FADH2 and COQH2 are similar in E0, thus similar in NRG, not a huge drop, and no ATP
more of a side mvmt (sideward motion)
quick generation of CoQH2/QH2
(formation of QH2 allows FADH2 to participate again in the Krebs cycle)
Complex 3
CoQ = ubiquinone = Q
CoQH2 can either come from complex I or II
complex I goes down to form it
complex II goes across to form it
in complex III, CoQH2 pass its e- to elements called cytochromes (bigger e- acceptors, they are
proteins w heme groups)
in inner membrane
cytochromes carry e- w the heme groups (hemoglobin and myoglobin carry O2)
exist in 2 oxidation states
red in colour
have Fe in centre of heme
can exist as ferrous (+2) OR ferric (+3)
o this is prevented in Hb and Mb bc it ruins the fx, but is encouraged in cytochromes in order
to transport e- as electron donors or acceptors
protons are released bc cytochromes can’t carry them
heme groups can only deal w e-
only 1 Fe per cytochrome, thus need 2 cytochromes to carry the 2 e- from CoQH2
cyt. c E0 is enough to generate ATP
big enough drop in reduction potential in complex II to generate ATP
Complex IV
cyt c is intermediate
the travelling molecule that goes bw complex II and IV
cyt c donor goes to a, a3
passes it s electrons to cyt c oxidase
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