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Lecture notes of 14 pages for the course Membrane and cellular Biochemistry at QMUL
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Mitochondrial respiratory chain & chemiosmotic hypothesisLearning objective:
1. Define the terms ‘standard redox potential’ and ‘redox couples’
2. Based on the standard redox potential of NADH and FADH2 discuss the different contributions of these reduced
coenzymes to oxidative phosphorylation.
3. Name the different types of electron carriers involved in the ETC and distinguish between their reduced and oxidised
forms
4. Identify the electron transfer steps in the ETC that provide sufficient free energy to move protons across the IMM
5. Explain how specific inhibitors can be used to determine the sequence of electron carriers in the ETC
6. name the integral membrane proteins of the ETC and summaries their functions in electron transport And H +
translocation
LO1. Standard redox potential
the capacity of a chemical or components to receive (take) electrons from hydrogen
positive redox potential = accept electrons
negative redox potential = donates electrons
LO1. Redox couple
is half the redox reaction
Electron transport chain
Is a series of complexes that transfer electrons from electron donors to electron acceptors via redox (reduction and
oxidation occurring simultaneously), reactions and couples this electron transfer with the transfer of protons across the
membrane (from the matrix to the inner membrane space).
Summary of oxidative phosphorylation
there are 4 complexes in the IMM of an ETC that are involved in respiration
Fundamental for cellular life
NADH has a negative redox potential (accepts electron)
FADH2 has a positive redox potential (donates electron)
NADH donating electron at a negative redox potential, which means that can donate to other components that are
negative, which is important because as we go down the ETC can slowly make the redox potential more positive if we
have many steps and in all the different steps can harvest (gather) the energy to pump protons
FAD is slightly less negative so it does not have the capacity for so many steps after the initial electron donation step.
, - Less energy for proton pumping by FADH2
Oxidation-reduction potentials (redox potentials)
Must have standard in biology
If we have a solution with 1 mole of proton and 1 mole of hydrogen in the reference half-cell followed by salt bridge with
redox couple in sample half-cell at ph. 0
The redox potential of both half-cells is not the same therefore electrons will move and we can measure movement of
electrons in Volts
NAD and NADH have a negative redox potential relative to hydrogen, which means that it is not likely to receive
electrons, more likely to give electrons
NADH donating electrons and 2 protons to make hydrogen, which gives a negative redox potential
This is the beginning of the respiratory transport chain
If move to the end of respiratory transport chain (the oxygen, water redox couple)
- At the end the electrons go to the oxygen
The redox potential is positive and more likely to receive electrons
Measure the voltage and get appositive redox potential
Positive redox potential = takes electron from hydrogen
Negative redox potential = donates electron from hydrogen
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