Week 6 Pt1 Flashcards
Complex 1
Pumps 4 protons Take electrons from NADH and deliver it to ubiquinone
Complex II
Pumps no protons Reduces the quinones We take protons from the negative side at complex II but we are not pushing it to the positive side Enzyme: succinate dehydrogenase Catalysed the transfer of electrons from succinate to FADH2 to ubiquinone (non transport of H+)
Complex III
Called cytochrome bc1 because 2 cytochromes are present Transports 4 protons across Catalysed the transfer of electrons from ubiquinone to cytochrome c
What do both complex I and complex II reduce?
Ubiquinone
What is electron transfer accompanied by?
Translocation of H+ across the inner mitochondrial membrane
Complex II is not a coupling site
No structural rearrangement It feeds electrons from succinate to IMM to reduce hydrophobic UQ to UQH2
Complex III
H+ translocation is coupled to oxidation of U1H2 to UQ Transition from 2 electron carrier (UQH2) to 1 electron carrier (cyt C)
How many quinone binding sites are there?
2 - one on the P side of the membrane and one is on N side of membrane
Complex IV
Catalyses transfer of electrons from cytochrome C released from complex III to oxygen Proton pumping across the membrane
How many electrons are required to reduce oxygen to water?
4 electrons
What holds iron in place?
A combination of cysteine side chain
Cysteine sulfhydryl
Inorganic sulphur
2 FE-S clusters
2 sulphurs do not include cysteine side chain
Just inorganic sulphur
4 FE-S clusters and 3 FE-S clusters
Different stoichiometry
Why is iron a limiting agent in biology?
It is not very accessible since the great oxygenation event
Fe2+ which is very bioacessible turned into Fe3+ which sank to the bottom of ocean
How many Fe-S clusters in the respiratory chain?
12 sites
What gives Fe-S clusters their redox potential?
Amino acids that surround them
Exposure to solvents
What reaction do Fe-S clusters generally carry out?
Single-electron transfers
Where is Fe-S found?
Complex I and II
Where is copper found?
Complex IV
What is oxygen consumption coupled to?
ATP synthesis
Method of ETC
- Set up oxygen electrode with 0.2ml purified mitochondria in 20ml solution as sample
- Add 20 microlitre ADP
- Inhibition is relieved by adding a substrate which enters after the inhibited complex
Rotenone
Inhibits complex I
Inhibit the transfer of electrons from Fe-S cluster in complex I to ubiquinone
Inhibits oxidation of NADH —> NAD+
No PMF
ATP synthase isn’t getting sufficient H+ to flow through this - less ATP
Decrease in oxygen consumption
Rotenone has no effect on oxidation of either succinct or ascorbate
What happens if there is no oxidation?
No transfer of electrons
No energy to pump the H+ ions from matrix into IMS
Anitmycin A
Inhibits either complex 2 or 3
Bind to Qi site on cytochrome C reductase in complex 3
This inhibits the oxidation of ubiquinone In Qi site of ubiquinol
This won’t allow protons coming from NADH/FADH oxidation to go into complex 3
ETC decreased - decrease in oxygen consumption
Flow of H+ from Matrix to IMS is reduced
Flow of protons through ATP synthase decrease
ATP synthesis decreased
Potassium cyanide
Inhibit complex 4
Bind to Iron in heme group of cytochrome oxidase C - associated with complex IV
Blocks transfer of electrons to oxygen
All complexes before that remain without an electron there is no passing of electrons down the chain and no PMF is established
Limited amount of ATP produced
What does complex I Contain?
FMN containing flavoprotein - oxidise NADH
8 distinct Fe-S clusters
2 bound molecule of ubiquinone
