MCB 300 Chapter 3.10-3.12, 14.13:
20 Feb 2019
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Lecture 15 revised material Reading sections: 3.10-3.12, 14.13
3.10 Respiration - Electron Carriers
● Central metabolism produces reduced cofactors like NADH and FADH2. The
oxidation of these cofactors back to NAD+ and FAD is linked to energy
conservation through the ETC.
● NADH Dehydrogenases and flavoproteins
○ ETC reactions are in the membranes of cells. The proteins and enzymes
that are in this chain are redox enzymes/proteins (NADH dehydrogenase,
flavoproteins, iron-sulfur proteins, cytochromes). There are also
non-proteins that participate - quinones. The proteins and non proteins
are arranged in the membrane in order of increasingly more positive
reduction potentials with NADH dehydrogenase first and the cytochromes
last.
3.11: energy conservation in respiration is linked to an energized state of the
membrane and this energized state is established by reactions of the ETC
● Electron Transport
○ The ETC carriers are oriented in the membrane so that redox reactions
can occur and so that H+ can go across the membrane. 2 electrons and 2
protons enter the ETC when NADH is oxidized to NAD+ to begin the
process of electron transport.
○ The membranes proteins and carriers are ordered so that they increase in
positive reduction potential and the final carrier in the chain donates the
electrons and the H+ to a terminal e- acceptor like O2.
○ H+ ions are extruded to the outer surface of the membrane. The inner and
outer surfaces differ in charge, pH, and electrochemical potential. The
difference in these are proton motive force and this energizes the
membrane like a battery.
● Generation of the PMF: Complex 1 and 2
○ The PMF forms from the activities of flavins, quinones, and cytochrome c
and the terminal proteins.
○ Complex = several proteins are present that function as a unit.
○ Complex 1 is NADH: quinone oxidoreductase because the overall reaction
is one in which NADH is oxidized and quinone is reduced. 2 H+ are taken
from the cytoplasm by Ub and is then reduced by Fe/S protein complex.
○ Complex 2 bypasses complex 1 and feeds electrons from FADH2 directly
to quinones. Complex 2 is succinate dehydrogenase because succinate
and FAs donate electrons when they are oxidized. Because complex 2
bypasses complex 1, 4 fewer H+ are pumped per 2 e- that enter from
FADH2
Document Summary
Lecture 15 revised material reading sections: 3. 10-3. 12, 14. 13. Central metabolism produces reduced cofactors like nadh and fadh2. The oxidation of these cofactors back to nad+ and fad is linked to energy conservation through the etc. Etc reactions are in the membranes of cells. The proteins and enzymes that are in this chain are redox enzymes/proteins (nadh dehydrogenase, flavoproteins, iron-sulfur proteins, cytochromes). There are also non-proteins that participate - quinones. The proteins and non proteins are arranged in the membrane in order of increasingly more positive reduction potentials with nadh dehydrogenase first and the cytochromes last. 3. 11: energy conservation in respiration is linked to an energized state of the membrane and this energized state is established by reactions of the etc. The etc carriers are oriented in the membrane so that redox reactions can occur and so that h+ can go across the membrane.
